this pilot study was an open - field research study that aimed to select and validate international classification of functioning , disability and health child and youth version codes commonly used for children with disabilities .
no core data set of international classification of functioning , disability and health child and youth version codes has yet been published , so codes were selected on the basis of an a priori judgement about which codes would best cover the range of types and magnitudes of disability under investigation .
codes and wording were subject to several revisions during a preliminary round of 25 interviews .
the set of codes and wordings resulting from this process were used throughout the rest of the study irrespective of disorder , severity of disability , age , or gender .
the codes were used to describe the performance of 332 children in activities of daily living .
children aged 1 to 15 years upon entry to the study were enrolled , and visits and interviews were conducted between october 1 , 2010 , and november 30 , 2011 . all children and their parents were known to us beforehand .
the hospital s electronic patient record system was used to identify all children in the region of southern denmark with muscular disorders , spina bifida , spinal muscular dystrophies , or disabilities following cerebral tumors .
children from funen island ( approximately 600 000 inhabitants ) , a minor geographical area within the southern danish region ( approximately 1.2 million inhabitants ) , with cerebral palsy , who were visually impaired or hearing impaired or had moderate to severe mental disability were recruited via the same method . as in international classification of functioning , disability and health , international classification of functioning ,
disability and health child and youth version uses a universal d code scoring system consisting of a 5-point likert - type scale with the following qualifiers:0 : no difficulty,1 : mild difficulty,2 : moderate difficulty,3 : severe difficulty , and4 : complete difficulty 
  2 : moderate difficulty , 3 : severe difficulty , and 4 : complete difficulty to enable a more detailed discussion of the child s needs , rather than simply focusing on the meaning of these basic definitions of level of impairment , d code qualifier levels were defined as follows:0 : child s ability is as expected for his or her age.1 : child has difficulties but activities and participation are still in the expected range for his or her age.2 : child needs help with activities and participation from another person.3 : child needs help and care due to only limited ability with respect to activities and participation.4 : child is totally dependent on others for activities and participation . 
  0 : child s ability is as expected for his or her age . 1 : child has difficulties but activities and participation are still in the expected range for his or her age . 2
: child needs help with activities and participation from another person . 3 : child needs help and care due to only limited ability with respect to activities and participation .
4 : child is totally dependent on others for activities and participation . the international classification of functioning , disability and health child and youth version data sheet and information on the study s aim and procedures were given to all families eligible for participation .
after 2 to 3 weeks , families were contacted by phone or in person at their homes , if necessary ; in this way , it was possible to make contact with every family .
participation in the study was entirely voluntary , and the decision to participate did not affect future clinical assignment .
all the families who agreed to participate were visited in their homes by one of the participating medical doctors ( noi , lwl , krb , ns , and mnj ) .
when the child lived in a residential facility , caregivers participated with the written consent of the child s parent or guardian .
factors related to the selected international classification of functioning , disability and health child and youth version codes and qualifiers were discussed with one or both parents .
international classification of functioning , disability and health child and youth version qualifiers were scored by one of us during conversation .
these datasheets were subsequently used for the manual transfer of data for analysis and were consulted whenever errors were suspected or spotted during subsequent data processing .
data on international classification of functioning , disability and health child and youth version b codes and environmental e codes were obtained simultaneously . within - scale analysis of responses from this single administration of d codes was undertaken .
if scores are to be summarized to form a single general assessment score , the codes should be internally consistent and measure the same underlying disability construct .
it is recommended that correlations between contributing d codes and the total score computed from the remaining codes , the corrected item  total correlations , should exceed .40 ( 26 ) .
data targeting was estimated from the code scale midpoint , range , and observed scores , together with floor and ceiling effects .
reliability was operationalized as internal consistency and estimated with cronbach  coefficient for average interitem correlation .
validity was determined by nonstatistical evaluation of the clinical meaning of the code scale and was further investigated in the rasch analysis . within - scale
factor analysis including the above - mentioned corrected item  total correlations and cronbach s  (  = nx 
 c 
 /.v 

+ ( n  1 )  
 c , where n = number of codes , 
 c = average inter code covariance and . 

v 
 = average variance , was used to calculate a score for a general assessment childhood disability construct .
the standard error of measurement = sd  (1  alpha ) , and 95% confidence intervals ( 95%cis ) =  1.96  standard error of measurement , were calculated .
stata 12 ( statacorp , college station , texas ) was used for data analysis .
a crucial aim of this pilot study was to generate as much information as possible about children s abilities and disabilities from the selected international classification of functioning , disability and health child and youth version codes and their qualifiers .
more specifically , the primary objective was to use the rasch model to generate a continuous scale that would be sensitive enough to register changes in disability that might not be distinguished by the ordinal international classification of functioning , disability and health child and youth version 5-point qualifier scales or international classification of functioning , disability and health child and youth version summations .
the rasch analysis model defines an individual s probability of success ( p ) on a given item in terms of the difference between the individual s ability ( b ) and item difficulty ( d ) .
p = exp(b  d)/1+exp(b  d ) or logp/(1  p ) = b 
d. probability of success ( p ) can also be expressed as log(odds ) = b  d or logit = b  d. in all further data analyses in this study , probability of success ( p ) in rasch terminology refers to probability of disability , person ( b ) refers to the child being assessed , and item difficulty ( d ) refers to the d code qualifiers .
rasch analysis was applied to all 5 qualifiers for the international classification of functioning , disability and health child and youth version d codes , and this assumes equal distances between qualifier levels , an assumption that can not be valid in clinical practice .
control for this was performed using a rasch model for polytomous data , the andrich rating - scale model . in practice ,
when a child s level of disability equals a certain qualifier level , b and d are identical , and the derived log(odds ) or logit value will be 0 . for codes in which the child s disability level is higher or lower , the relevant logit value will be correspondingly positive or negative .
a logit scale that is independent of whether disability level is assessed by the d code qualifier level is generated .
this scale constitutes the latent disability construct or variable for the children included in this study and the d codes and qualifiers used .
graphically , values of the disability variable form a sigmoid curve where the x - axis is a logit scale . the ordinal scale originally representing the international classification of functioning , disability and health child and youth version scores can be mapped to a scale that detects changes that lie between the individual steps of the ordinal scale .
most importantly , the d code qualifier scores can be added to provide a true total score . for individual children and specific d codes and their qualifiers to contribute to the formation of the disability variable
, certain validity criteria must be met : ( a ) adequacy of targeting children and d codes , ( b ) construction of measurement ruler , and ( c ) successful measurement of children .
these areas have been described by the authors in detail and will be dealt with in the results section .
this pilot study was an open - field research study that aimed to select and validate international classification of functioning , disability and health child and youth version codes commonly used for children with disabilities .
no core data set of international classification of functioning , disability and health child and youth version codes has yet been published , so codes were selected on the basis of an a priori judgement about which codes would best cover the range of types and magnitudes of disability under investigation .
codes and wording were subject to several revisions during a preliminary round of 25 interviews .
the set of codes and wordings resulting from this process were used throughout the rest of the study irrespective of disorder , severity of disability , age , or gender .
the codes were used to describe the performance of 332 children in activities of daily living .
children aged 1 to 15 years upon entry to the study were enrolled , and visits and interviews were conducted between october 1 , 2010 , and november 30 , 2011 . all children and their parents were known to us beforehand .
the hospital s electronic patient record system was used to identify all children in the region of southern denmark with muscular disorders , spina bifida , spinal muscular dystrophies , or disabilities following cerebral tumors .
children from funen island ( approximately 600 000 inhabitants ) , a minor geographical area within the southern danish region ( approximately 1.2 million inhabitants ) , with cerebral palsy , who were visually impaired or hearing impaired or had moderate to severe mental disability were recruited via the same method .
as in international classification of functioning , disability and health , international classification of functioning , disability and health child and youth version uses a universal d code scoring system consisting of a 5-point likert - type scale with the following qualifiers:0 : no difficulty,1 : mild difficulty,2 : moderate difficulty,3 : severe difficulty , and4 : complete difficulty 
  2 : moderate difficulty , 3 : severe difficulty , and 4 : complete difficulty to enable a more detailed discussion of the child s needs , rather than simply focusing on the meaning of these basic definitions of level of impairment , d code qualifier levels were defined as follows:0 : child s ability is as expected for his or her age.1 : child has difficulties but activities and participation are still in the expected range for his or her age.2 : child needs help with activities and participation from another person.3 : child needs help and care due to only limited ability with respect to activities and participation.4 : child is totally dependent on others for activities and participation . 
  0 : child s ability is as expected for his or her age . 1 : child has difficulties but activities and participation are still in the expected range for his or her age . 2
: child needs help with activities and participation from another person . 3 : child needs help and care due to only limited ability with respect to activities and participation .
the international classification of functioning , disability and health child and youth version data sheet and information on the study s aim and procedures were given to all families eligible for participation .
after 2 to 3 weeks , families were contacted by phone or in person at their homes , if necessary ; in this way , it was possible to make contact with every family .
participation in the study was entirely voluntary , and the decision to participate did not affect future clinical assignment .
all the families who agreed to participate were visited in their homes by one of the participating medical doctors ( noi , lwl , krb , ns , and mnj ) .
when the child lived in a residential facility , caregivers participated with the written consent of the child s parent or guardian .
factors related to the selected international classification of functioning , disability and health child and youth version codes and qualifiers were discussed with one or both parents .
international classification of functioning , disability and health child and youth version qualifiers were scored by one of us during conversation .
these datasheets were subsequently used for the manual transfer of data for analysis and were consulted whenever errors were suspected or spotted during subsequent data processing .
data on international classification of functioning , disability and health child and youth version b codes and environmental e codes were obtained simultaneously .
within - scale analysis of responses from this single administration of d codes was undertaken .
if scores are to be summarized to form a single general assessment score , the codes should be internally consistent and measure the same underlying disability construct .
it is recommended that correlations between contributing d codes and the total score computed from the remaining codes , the corrected item  total correlations , should exceed .40 ( 26 ) .
data targeting was estimated from the code scale midpoint , range , and observed scores , together with floor and ceiling effects .
reliability was operationalized as internal consistency and estimated with cronbach  coefficient for average interitem correlation .
validity was determined by nonstatistical evaluation of the clinical meaning of the code scale and was further investigated in the rasch analysis . within - scale factor analysis including the above - mentioned corrected item  total correlations and cronbach s  (  = nx 
 c 
 /.v 

+ ( n  1 )  
 c , where n = number of codes , 
 c = average inter code covariance and . 

v 
 = average variance , was used to calculate a score for a general assessment childhood disability construct .
the standard error of measurement = sd  (1  alpha ) , and 95% confidence intervals ( 95%cis ) =  1.96  standard error of measurement , were calculated .
stata 12 ( statacorp , college station , texas ) was used for data analysis .
a crucial aim of this pilot study was to generate as much information as possible about children s abilities and disabilities from the selected international classification of functioning , disability and health child and youth version codes and their qualifiers .
more specifically , the primary objective was to use the rasch model to generate a continuous scale that would be sensitive enough to register changes in disability that might not be distinguished by the ordinal international classification of functioning , disability and health child and youth version 5-point qualifier scales or international classification of functioning , disability and health child and youth version summations .
the rasch analysis model defines an individual s probability of success ( p ) on a given item in terms of the difference between the individual s ability ( b ) and item difficulty ( d ) .
p = exp(b  d)/1+exp(b  d ) or logp/(1  p ) = b  d. probability of success ( p ) can also be expressed as log(odds ) = b  d or logit = b  d. in all further data analyses in this study , probability of success ( p ) in rasch terminology refers to probability of disability , person ( b ) refers to the child being assessed , and item difficulty ( d ) refers to the d code qualifiers .
rasch analysis was applied to all 5 qualifiers for the international classification of functioning , disability and health child and youth version d codes , and this assumes equal distances between qualifier levels , an assumption that can not be valid in clinical practice .
control for this was performed using a rasch model for polytomous data , the andrich rating - scale model . in practice , when a child s level of disability equals a certain qualifier level , b and d are identical , and the derived log(odds ) or logit value will be 0 . for codes
in which the child s disability level is higher or lower , the relevant logit value will be correspondingly positive or negative .
a logit scale that is independent of whether disability level is assessed by the d code qualifier level is generated .
this scale constitutes the latent disability construct or variable for the children included in this study and the d codes and qualifiers used .
graphically , values of the disability variable form a sigmoid curve where the x - axis is a logit scale . the ordinal scale originally representing the international classification of functioning , disability and health child and youth version scores can be mapped to a scale that detects changes that lie between the individual steps of the ordinal scale .
most importantly , the d code qualifier scores can be added to provide a true total score .
for individual children and specific d codes and their qualifiers to contribute to the formation of the disability variable , certain validity criteria must be met : ( a ) adequacy of targeting children and d codes , ( b ) construction of measurement ruler , and ( c ) successful measurement of children .
these areas have been described by the authors in detail and will be dealt with in the results section .
the parents of 35 children decided not to participate for various reasons ; thus , 332 ( 90.5% ) children were included whose parents or caregivers completed the interview .
the children included had a mean age of 9.4 years , standard deviation 3.8 years , and age range 1.0 to 15.9 years . before the first visit , each child s medical record was reviewed , and data on discharge diagnosis and associated diagnoses were recorded to ensure that the information used in the study was as up to date as possible . the parents and caregivers of 12 children
the children of the participating parents were grouped according to discharge diagnosis , and 63 children had a discharge diagnosis of spina bifida , 8 had spinal muscular atrophy , 36 had muscular disorders , 157 had cerebral palsy , 8 were visually impaired , 13 were hearing impaired , 11 had a mental disability , and 36 had been diagnosed with and treated for brain tumors .
there was missing data for 57 d codes in 394 ( 3.7% ) of 10 624 responses .
this was due to the fact that some children were not old enough to be evaluated with respect to certain d codes .
it was decided not to set age thresholds for applicability of specific d codes , and the decision about whether or not to assign a score for a particular code was made on an individual basis .
total correlations for the d codes ( .76 ) , high intercode correlations ( .61 ) , and high reliability in terms of cronbach  ( .98 ) . means and standard deviations for observed scores for the codes were to the left of the ranges , indicating that a fairly high proportion of the sample had lower levels of disability .
the d codes selected ( table 1 ) along with disability level corresponding to children s disability ( targeting ) are illustrated in the child - code map for d codes ( figure 1 ) .
data on d codes were pooled in relation to children with more severe disabilities ( figure 1 ) .
this was due to the fact that a relatively large proportion of the sample had relatively minor difficulties .
international classification of functioning , disability and health child and youth version d codes initially used in the sample of 332 children , which fit the rasch model ( n = 39 ) . 
 

subcategories of d codes are given by the first digit and are coded as follows : ( 1 ) mental functions ; ( 2 ) sensory functions and pain ; ( 3 ) voice and speech functions ; ( 4 ) functions of the cardiovascular , hematological , immunological , and respiratory systems ; ( 5 ) functions of the digestive , metabolic , and endocrine systems ; ( 6 ) genitourinary and reproductive functions ; ( 7 ) neuromusculoskeletal and movement - related functions ; and ( 8) functions of the skin and related structures distribution of the 39 d codes that fit the rasch model among the 332 children in the sample . each 
m indicates mean , s = 1 standard deviation and t = 2 standard deviations .
each d code location equals the mean of 1 , 2 , 3 , and 4 ; thus , d codes apply to children far below and above their mean locations .
the mean s of all 39 d codes are illustrated in figure 2 ; and the figure shows that there was a fairly equal probability of observing adjacent qualifiers .
qualifier 0 = red , 1 = blue , 3 = purple and 4 = black .
the  values are where those curves meet , indicating 50% probability of either qualifier being answered .
if qualifier definitions were misunderstood and/or formulated in a problematic way , the probability curves would not follow qualifier ordering .
structure calibration across all qualifier levels for the 39 d codes selected showed that  thresholds and category measures increased with increasing qualifier values ( table 2 ) , that is , they were ordered .
the range and order of d codes on the disability variable seem to be clinically sound .
for many of the children in the sample , lower extremity motor difficulties were the major disability , and they had normal cognitive ability .
d4750 ( riding a bicycle ) was the d code which most commonly registered impairment in the least disabled children , with d5101 ( washing whole body ) and d710 ( basic interpersonal interactions ) registering impaired functioning when there was a cognitive dimension to the child s disability .
codes related to perception , for example , d3150 ( communicating with receiving body gestures ) , made an important contribution to the assessment of disability only in children who were severely disabled ( figure 1 ) .
thereafter , no d codes showed infit or outfit mean squares ( mnsqs ) > 2.0 , and the data demonstrated a proper fit .
international classification of functioning , disability and health child and youth version d codes initially used which did not fit the rasch model ( n = 18 ) . 
 

codes marked * showed infit and/or outfit mnsq values > 1.5 ; codes marked * * also showed qualifier disordering .
codes marked  correlated with codes in ( ) . the codes marked  were retained due to better fit than those in ( ) .
the standardized fit statistics ( zstd ) values reflect the probability that a given mnsq value occurs by chance when the data fits the rasch model . a positive zstd
seven d codes had high outfit zstds , and 3 d codes had high infit zstds .
measure correlations were all close to expected values , as individual d code correlations were related to other d code correlations in the same child .
none of the correlations were negative , indicating that all the d codes contributed to the disability variable and that the data for the selected d codes was unidimensional .
there is an exact match between the child s functioning and d code difficulty when d code difficulty is identical to the child s disability .
an observed percentage higher than the expected percentage on a measure indicates a higher probability of an exact match .
high within - code category correlations are not desirable . in the 10 most highly correlated d code pairs ,
an approximate t test for the dif for each d code against overall d codes difficulty was conducted using critical values 2.0 . around 50% of d codes had t in the range 2.0 to 3.0 , but some codes had a higher t. the separation index was 7.8 for d codes , indicating that more than 3 levels of d codes could be differentiated with a reliability of 0.98 .
the number of children with infit mnsq 1.5 to 2.0 was 36 , and 9 children had infit mnsq > 2.0 ( range : 2.04 - 2.64 ) . thirty - three children had outfit mnsq 1.5 to 2.0 , and 13 children had outfit mnsq > 2.0 ( range : 2.01 3.37 ) , giving 16 children with either infit or outfit mnsq > 2.0 .
the person separation index ( psi ) for d codes was 3.49 , with reliability of .92 , indicating that 3 different levels of disability could be distinguished statistically using this group of d codes with the same standard deviation of 1.51 .
mean location on the d code - based disability variable was 1.33 , standard deviation 2.04 , and the highest location was 4.73 and the lowest 4.47 .
this highest and lowest score data did not correspond exactly with the data on the child - code map ( figure 1 ) , reflecting the fact that in rasch analysis , extreme data are less reliable .
the parents of 35 children decided not to participate for various reasons ; thus , 332 ( 90.5% ) children were included whose parents or caregivers completed the interview .
the children included had a mean age of 9.4 years , standard deviation 3.8 years , and age range 1.0 to 15.9 years . before the first visit , each child s medical record was reviewed , and data on discharge diagnosis and associated diagnoses were recorded to ensure that the information used in the study was as up to date as possible . the parents and caregivers of 12 children
the children of the participating parents were grouped according to discharge diagnosis , and 63 children had a discharge diagnosis of spina bifida , 8 had spinal muscular atrophy , 36 had muscular disorders , 157 had cerebral palsy , 8 were visually impaired , 13 were hearing impaired , 11 had a mental disability , and 36 had been diagnosed with and treated for brain tumors .
there was missing data for 57 d codes in 394 ( 3.7% ) of 10 624 responses .
this was due to the fact that some children were not old enough to be evaluated with respect to certain d codes .
it was decided not to set age thresholds for applicability of specific d codes , and the decision about whether or not to assign a score for a particular code was made on an individual basis .
total correlations for the d codes ( .76 ) , high intercode correlations ( .61 ) , and high reliability in terms of cronbach  ( .98 ) . means and standard deviations for observed scores for the codes were to the left of the ranges , indicating that a fairly high proportion of the sample had lower levels of disability .
the d codes selected ( table 1 ) along with disability level corresponding to children s disability ( targeting ) are illustrated in the child - code map for d codes ( figure 1 ) .
data on d codes were pooled in relation to children with more severe disabilities ( figure 1 ) .
this was due to the fact that a relatively large proportion of the sample had relatively minor difficulties .
international classification of functioning , disability and health child and youth version d codes initially used in the sample of 332 children , which fit the rasch model ( n = 39 ) . 
 

subcategories of d codes are given by the first digit and are coded as follows : ( 1 ) mental functions ; ( 2 ) sensory functions and pain ; ( 3 ) voice and speech functions ; ( 4 ) functions of the cardiovascular , hematological , immunological , and respiratory systems ; ( 5 ) functions of the digestive , metabolic , and endocrine systems ; ( 6 ) genitourinary and reproductive functions ; ( 7 ) neuromusculoskeletal and movement - related functions ; and ( 8) functions of the skin and related structures distribution of the 39 d codes that fit the rasch model among the 332 children in the sample .
m indicates mean , s = 1 standard deviation and t = 2 standard deviations .
each d code location equals the mean of 1 , 2 , 3 , and 4 ; thus , d codes apply to children far below and above their mean locations .
the mean s of all 39 d codes are illustrated in figure 2 ; and the figure shows that there was a fairly equal probability of observing adjacent qualifiers .
qualifier 0 = red , 1 = blue , 3 = purple and 4 = black .
the  values are where those curves meet , indicating 50% probability of either qualifier being answered .
if qualifier definitions were misunderstood and/or formulated in a problematic way , the probability curves would not follow qualifier ordering .
structure calibration across all qualifier levels for the 39 d codes selected showed that  thresholds and category measures increased with increasing qualifier values ( table 2 ) , that is , they were ordered .
the range and order of d codes on the disability variable seem to be clinically sound . for many of the children in the sample ,
lower extremity motor difficulties were the major disability , and they had normal cognitive ability .
this accounts for the frequency ordering of the codes : d4750 ( riding a bicycle ) was the d code which most commonly registered impairment in the least disabled children , with d5101 ( washing whole body ) and d710 ( basic interpersonal interactions ) registering impaired functioning when there was a cognitive dimension to the child s disability .
codes related to perception , for example , d3150 ( communicating with receiving body gestures ) , made an important contribution to the assessment of disability only in children who were severely disabled ( figure 1 ) . all d codes with disordered qualifiers were excluded ( table 3 ) .
thereafter , no d codes showed infit or outfit mean squares ( mnsqs ) > 2.0 , and the data demonstrated a proper fit . international classification of functioning , disability and health child and youth version d codes initially used which did not fit the rasch model ( n = 18 ) . 
 

codes marked * showed infit and/or outfit mnsq values > 1.5 ; codes marked * * also showed qualifier disordering .
codes marked  correlated with codes in ( ) . the codes marked  were retained due to better fit than those in ( ) . the standardized fit statistics ( zstd ) values reflect the probability that a given mnsq value occurs by chance when the data fits the rasch model . a positive zstd
seven d codes had high outfit zstds , and 3 d codes had high infit zstds .
measure correlations were all close to expected values , as individual d code correlations were related to other d code correlations in the same child .
none of the correlations were negative , indicating that all the d codes contributed to the disability variable and that the data for the selected d codes was unidimensional .
there is an exact match between the child s functioning and d code difficulty when d code difficulty is identical to the child s disability .
an observed percentage higher than the expected percentage on a measure indicates a higher probability of an exact match .
high within - code category correlations are not desirable . in the 10 most highly correlated d code pairs ,
for both code categories , the maximum correlation coefficient was < .7 , indicating a satisfactory level of correlation .
an approximate t test for the dif for each d code against overall d codes difficulty was conducted using critical values 2.0 . around 50% of d codes had t in the range 2.0 to 3.0 , but some codes had a higher t. the separation index was 7.8 for d codes , indicating that more than 3 levels of d codes could be differentiated with a reliability of 0.98 .
the number of children with infit mnsq 1.5 to 2.0 was 36 , and 9 children had infit mnsq > 2.0 ( range : 2.04 - 2.64 ) .
thirty - three children had outfit mnsq 1.5 to 2.0 , and 13 children had outfit mnsq > 2.0 ( range : 2.01 3.37 ) , giving 16 children with either infit or outfit mnsq > 2.0 .
the person separation index ( psi ) for d codes was 3.49 , with reliability of .92 , indicating that 3 different levels of disability could be distinguished statistically using this group of d codes with the same standard deviation of 1.51 .
mean location on the d code - based disability variable was 1.33 , standard deviation 2.04 , and the highest location was 4.73 and the lowest 4.47 .
this highest and lowest score data did not correspond exactly with the data on the child - code map ( figure 1 ) , reflecting the fact that in rasch analysis , extreme data are less reliable .
the d codes selected ( table 1 ) along with disability level corresponding to children s disability ( targeting ) are illustrated in the child - code map for d codes ( figure 1 ) .
data on d codes were pooled in relation to children with more severe disabilities ( figure 1 ) .
this was due to the fact that a relatively large proportion of the sample had relatively minor difficulties .
international classification of functioning , disability and health child and youth version d codes initially used in the sample of 332 children , which fit the rasch model ( n = 39 ) . 
 

subcategories of d codes are given by the first digit and are coded as follows : ( 1 ) mental functions ; ( 2 ) sensory functions and pain ; ( 3 ) voice and speech functions ; ( 4 ) functions of the cardiovascular , hematological , immunological , and respiratory systems ; ( 5 ) functions of the digestive , metabolic , and endocrine systems ; ( 6 ) genitourinary and reproductive functions ; ( 7 ) neuromusculoskeletal and movement - related functions ; and ( 8) functions of the skin and related structures distribution of the 39 d codes that fit the rasch model among the 332 children in the sample .
m indicates mean , s = 1 standard deviation and t = 2 standard deviations .
each d code location equals the mean of 1 , 2 , 3 , and 4 ; thus , d codes apply to children far below and above their mean locations .
the mean s of all 39 d codes are illustrated in figure 2 ; and the figure shows that there was a fairly equal probability of observing adjacent qualifiers .
qualifier 0 = red , 1 = blue , 3 = purple and 4 = black .
the  values are where those curves meet , indicating 50% probability of either qualifier being answered .
if qualifier definitions were misunderstood and/or formulated in a problematic way , the probability curves would not follow qualifier ordering .
structure calibration across all qualifier levels for the 39 d codes selected showed that  thresholds and category measures increased with increasing qualifier values ( table 2 ) , that is , they were ordered .
the range and order of d codes on the disability variable seem to be clinically sound .
for many of the children in the sample , lower extremity motor difficulties were the major disability , and they had normal cognitive ability .
this accounts for the frequency ordering of the codes : d4750 ( riding a bicycle ) was the d code which most commonly registered impairment in the least disabled children , with d5101 ( washing whole body ) and d710 ( basic interpersonal interactions ) registering impaired functioning when there was a cognitive dimension to the child s disability . codes related to perception , for example , d3150 ( communicating with receiving body gestures ) , made an important contribution to the assessment of disability only in children who were severely disabled ( figure 1 ) .
thereafter , no d codes showed infit or outfit mean squares ( mnsqs ) > 2.0 , and the data demonstrated a proper fit . international classification of functioning , disability and health child and youth version d codes initially used which did not fit the rasch model ( n = 18 ) . 
 

codes marked * showed infit and/or outfit mnsq values > 1.5 ; codes marked * * also showed qualifier disordering .
codes marked  correlated with codes in ( ) . the codes marked  were retained due to better fit than those in ( ) . the standardized fit statistics ( zstd ) values reflect the probability that a given mnsq value occurs by chance when the data fits the rasch model .
seven d codes had high outfit zstds , and 3 d codes had high infit zstds .
measure correlations were all close to expected values , as individual d code correlations were related to other d code correlations in the same child .
none of the correlations were negative , indicating that all the d codes contributed to the disability variable and that the data for the selected d codes was unidimensional .
there is an exact match between the child s functioning and d code difficulty when d code difficulty is identical to the child s disability . an observed percentage higher than the expected percentage on a measure indicates a higher probability of an exact match .
high within - code category correlations are not desirable . in the 10 most highly correlated d code pairs ,
for both code categories , the maximum correlation coefficient was < .7 , indicating a satisfactory level of correlation .
an approximate t test for the dif for each d code against overall d codes difficulty was conducted using critical values 2.0 . around
50% of d codes had t in the range 2.0 to 3.0 , but some codes had a higher t. the separation index was 7.8 for d codes , indicating that more than 3 levels of d codes could be differentiated with a reliability of 0.98 .
the number of children with infit mnsq 1.5 to 2.0 was 36 , and 9 children had infit mnsq > 2.0 ( range : 2.04 - 2.64 ) . thirty - three children had outfit mnsq 1.5 to 2.0 , and 13 children had outfit mnsq > 2.0 ( range : 2.01 3.37 ) , giving 16 children with either infit or outfit mnsq > 2.0 .
the person separation index ( psi ) for d codes was 3.49 , with reliability of .92 , indicating that 3 different levels of disability could be distinguished statistically using this group of d codes with the same standard deviation of 1.51 .
mean location on the d code - based disability variable was 1.33 , standard deviation 2.04 , and the highest location was 4.73 and the lowest 4.47 .
this highest and lowest score data did not correspond exactly with the data on the child - code map ( figure 1 ) , reflecting the fact that in rasch analysis , extreme data are less reliable .
this study was undertaken to find out how international classification of functioning , disability and health child and youth version activities and participation d codes and qualifiers might be used in clinical practice .
a sample of 332 children with various diseases was analyzed , encompassing the broadest possible range of disabilities , ranging from children with almost no symptoms to children who were totally physically dependent and including children who were mentally disabled , visually impaired , or hearing impaired . in order to facilitate the use of qualifiers by providing definitions that were as explicit as possible ,
the qualifiers were worded in terms of the level of help needed in the child s activities of daily life , relative to unimpaired age peers . once explained in conversations during visits , parents and caregivers had no difficulty judging which qualifier level was most appropriate for their child . in order to ensure that data obtained would be suitable for statistical analysis , codes were defined explicitly .
furthermore , when applying rasch data analysis codes that do not fit might be rejected and thereby lost .
if wording is no , mild , moderate , severe , or complete , problem there might be difficulty rescuing important codes . if codes are worded , however , the wording might be readdressed , possibly changed , reintroduced , and thereby be subject for future rasch analysis .
also , qualifier wording in terms of need for help universally across the disease diagnosis was considered although with different means for help .
for the same reason , it is necessary to know the details of an individual s condition .
the international classification of diseases , tenth revision codes and international classification of functioning , disability and health child and youth version codes are therefore considered as complementary and should be considered together in future data system implementations , clinical data handling , communications , evaluations , and research .
the international classification of functioning , disability and health child and youth version activities and participation d codes exhibited widely varying code means , variances , and standard errors of measurement on a 95% confidence level , making it difficult to construct a unitary disability variable on the basis of psychometric data analysis alone , although the mean corrected code 
this is important , as this study sought to determine whether a unitary and single disability variable might be used to characterize disability across conditions , types , and severity of disability .
this would avoid the need to have different sets of disability variables for different clinical diagnoses .
it seemed possible to demonstrate that the data obtained could be described in terms of a single disability variable .
the child - code maps ( person  item maps ) for activities and participation d codes seemed sound , and children with only minor motor problems were located at the lower end of the range of the disability variable and those with severe and complex disabilities at the upper end of the range . a relatively large proportion of the children had motor difficulties only .
this meant that an important group of the activities and participation d codes were located in the upper half of the range of the disability variable , as they were only relevant to the more disabled children who had both motor and cognitive difficulties .
position on the continuum for the disability variable corresponded well with the complexity and severity of the factors assessed by particular activities and participation d codes ( figure 1 ) .
particular concern was shown in determining whether activities and participation d codes behaved differently across diagnoses , ages , and genders .
differential item functioning seemed fair across most items for all these child characteristics , although consistency was least satisfactory across age , with t values close to 2 or 2 for some items .
age of the child has not yet been specifically addressed in international classification of functioning , disability and health child and youth version terms , as this variable belongs to personal factors .
also , international classification of functioning , disability and health child and youth version codes are seen as universal across age . during interviews with parents , each child s disabilities
were always compared to what could be expected of a healthy child at corresponding age .
they provided information based on their knowledge and experience of the children , and they participated in all international classification of functioning , disability and health child and youth version qualifier assessments , and the authors recognized the value of their active contribution .
all participating parents were very dedicated and honest , and it is believed that this will also be true more generally .
if biased assessment was to occur , it could be uncovered by analyzing nonreflected assessments in terms of infit data and exaggerated assessments in terms of outfit data . in conclusion
, it is believed that a combination of international classification of diseases , tenth revision codes , a common set of international classification of functioning , disability and health child and youth version d codes for activities and participation and further international classification of functioning , disability and health child and youth version body functions codes , environmental codes , and personal codes could provide a good tool for the assessment of functioning in all children with disabilities of varying types and magnitudes .
rasch analysis should be part of this tool , as it adds very necessary power to international classification of functioning , disability and health child and youth version that provides the best possible assessment of an individual child or population of children over time .
this could be achieved by equipping parents , hospital- and community - based health workers , and social workers with access to a common and electronic network that is permanently available and updateable .
functions of codes could then be analyzed repeatedly , and codes could be added or subtracted to the code set employed .
thus , the methodology demonstrates a mode of selecting both comprehensive and core data sets .
most importantly , international classification of functioning , disability and health child and youth version code data could be obtained whenever needed , whether when dealing with health problems , sharing information among service providers , or for accreditation and research purposes .
the authors hope this study will inspire the implementation of such a program , stimulate further research in this important field , and be of benefit to children with disabilities .
 aim : evaluation of the international classification of functioning , disability and health child and youth version ( icf - cy ) activities and participation d code functions in clinical practice with children across diagnoses , disabilities , ages , and genders.methods:a set of 57 codes were selected and worded to describe children s support needs in everyday life . 
 parents of children aged 1 to 15 years participated in interviews to discuss and rate their child s disability.results:of 367 invited parents , 332 ( 90.5% ) participated . 
 the mean age of their children with disability was 9.4 years . 
 the mean code scores were 50.67 , the corrected code  
 total correlations were .76 , intercode correlations had the mean of 0.61 , and cronbach s  was .98 . as a result of rasch analysis , graphical data for disability measures paralleled clinical expectations across the total population of 332 children.conclusion:the world health organization international classification of functioning , disability and health child and youth version d code data can provide a coherent measure of severity of disability in children across various diagnoses , ages , and genders . 
Methods
Study Design and Children With Disabilities
Qualifier-Level Wording
Procedures
Psychometric Evaluation of International Classification of Functioning, Disability and Health Child and Youth Version d Code Data
Rasch Modeling Data
Results
Descriptive Characteristics
Results of Psychometric Analyses of d Codes
Results of Rasch Analysis d Code Scores
(A) Adequacy of targeting children and d codes
(B) Construction of measurement ruler
(C) Successful measurement of children
Discussion