by 2017 , korea will be an aging society , with over 14.0% of its population being over 
 65  years old ; by 2026 , it will be a super - aged society , with the elderly accounting for over 
 20.0% of the population1 .
for this reason , 
 gerontology research is becoming increasingly important , especially that centered on the 
 measurement and evaluation of elderly health status2 , 
 3 . in order to measure the health status of the elderly accurately
, the concept of health 
 should be clearly defined in terms of present societal demands .
disease free4 , nowadays contains aspects related to quality of life in addition to 
 the absence of disease5 . due to this 
 change in the definition of health
, the use of a scale developed according to the former 
 definition would be obviously problematic in the present aging society .
unfortunately , 
 numerous existing measures of health status of adults or the elderly adhere to the former 
 definition .
one of these , the 36-item short form health survey ( sf-36 ) has come to serve as 
 a representative general health status and treatment efficacy assessment scale since its 
 development6,7,8 .
the sf-36 has been used in 
 health science , medicine , and physical education among other fields .
furthermore , it has 
 been translated into several languages , including korean , and it is widely used as a measure 
 of the health status of korean elderly adults .
its validity in the adult and elderly 
 population of korea has also been confirmed .
for example , nam and lee4 , who studied adults , and han and lee9 , who studied the elderly , demonstrated the construct 
 validity of the sf-36 through exploratory and confirmatory factor analyses . however , factor 
 analysis by itself does not accurately confirm a scale s validity , especially when it is 
 applied to a group other than the original10 .
furthermore , it can not verify the structure of the sub - components 
 and the difficulty level of the items11 .
this model is based on item response theory , and it evaluates the 
 appropriateness of the number of items in a scale and calculates the fit of the items to the 
 data and the difficulty of these items .
the rasch model is also able to evaluate the 
 suitability of the response method ( e.g. , five- or four - point scales ) for subjects13 .
furthermore , it can detect overlapping 
 and incongruent items , which can be confusing to subjects14,15,16 .
for these reasons , it is feasible and desirable to employ the 
 rasch methodology to confirm the validity of the sf-36 for elderly korean adults .
setting and samples : this study surveyed elderly people over the age of 60 by distributing 
 the sf-36 questionnaire at senior welfare centers in the seoul and gyeonggi areas of south 
 korea . an investigator explained and completed each item for those elderly persons who were 
 unable to complete the self - administered questionnaire .
the distribution of subjects 
 according to gender and age is shown in table 
 1table 1.distribution of subjects according to age and genderagemalefemaletotal606412 ( 2.4%)16 ( 3.1%)28 ( 5.5%)656953 ( 10.4%)109 ( 21.4%)162 ( 31.8%)707486 ( 16.9%)103 ( 20.2%)189 ( 37.1%)757931 ( 6.1%)43 ( 8.4%)74 ( 14.5%)over 8022 ( 4.3%)35 ( 6.9%)57 ( 11.2%)total204 ( 40.0%)306 ( 60.0%)510 ( 100% ) .
this study was approved by the public institutional review board of the korea ministry of 
 health and welfare ( p01 - 201303-sb-07 - 00 ) and conforms to the principles of the declaration 
 of helsinki .
furthermore , we received permission to use the sf-36 from the company that 
 owns it ( optuminsight life sciences , inc . ,
measurements / instruments : the sf-36 scale was developed by ware and sherboune17 , and was adapted by koh et al.18 to measure the quality of life of elderly 
 koreans .
it consists of 36 items categorized as follows : 10 items of physical functioning , 
 four items of role limitation  physical , two items of bodily pain , five items of general 
 health , four items of vitality , two items of social functioning , three items of role 
 limitation  emotion , five items of mental health , and one item of health changes .
the items 
 concerning physical functioning are answered on a three - point scale , while those concerning 
 bodily pain are answered on a five or six - point scale ; the rest of the items are answered on 
 a five - point scale . in general , higher scores indicate better health status ; however , three 
 items of general health , one item of social functioning , two items of vitality , two items of 
 mental health , the two items of bodily pain , and the item of health changes are reverse 
 scored .
the sequence of the items in the present study was randomized to increase 
 measurement validity .
the sf-36 subscales and the number of items are shown in table 2table 2.sf-36 dimensions and the number and sequence of itemsdimensionnumber of itemssequence of itemsphysical functioning103 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12social functioning220 , 32role limitation 
emotional317 , 18 , 19mental health524 , 25 , 26 , 28 , 30vitality423 , 27 , 29 , 31bodily pain221 , 22general health51 , 33 , 34 , 35 , 36health changes12total36sf-36 , 36-item short form survey .
sf-36 , 36-item short form survey we used rasch analysis to examine the validity of the sf-36 .
first , we conducted a 
 principal component analysis to determine the unidimensionality of the items , as this is a 
 fundamental condition of the rasch model .
this was done by calculating whether the items of 
 each factor share equal variance19 using 
 spss 20.0 ( spss , chicago , il , usa ) . in principal component analysis
, the scale is considered 
 unidimensional if the eigenvalue of the first component is greater than 1.00 or if the 
 largest principal component accounts for over 20% of the total variance20 .
goodness - of - fit was then examined using winsteps 3.65.0 
 ( rasch measurement software , usa ) .
an item was regarded as inappropriate if its 
 goodness - of - fit ( infit and outfit ) indexes were more than 1.30 or less than 0.7021 .
furthermore , the suitability of the 
 rating scales of the items was evaluated through step calibration in the probability curve . 

step calibration examines the appropriateness of the rating scales of the items by dividing 
 subjects numerical response scores by the number of responses in the scale ( three - point , 
 five - point , or six - point scale ) .
the response scale appropriateness is expressed as 
 thresholds , which are calculated from each factor s item characteristic curve22 .
health status is considered to have an 
 appropriate response scale if the step calibration of the scale applied to each factor ( the 
 adjustment value ) increases gradually towards as high scale score23 , 24 .
social 
 functioning , bodily pain , and health change , which consist of less than two items each , were 
 excluded from this analysis .
unidimensionality verification : the results of the principal component analysis used to 
 test the unidimensionality are displayed in table 
 3table 3.results of principal component analysis of sf-36factorfirst componenteigenvaluesecond componenteigenvaluevariance of firstcomponent eigenvalue ( % ) physical functioning6.411.1864.13role limitation 
all six factors together accounted for over 20% of the variance ( effect size ) 
 of the first component eigenvalue .
furthermore , the variances of the first component 
 eigenvalue in physical functioning , role limitation  physical , role limitation  emotion , 
 mental health , vitality , and general health were 64.13% , 89.51% , 91.31% , 62.43% , 65.34% , and 
 61.46% respectively ; thus , the criteria of unidimensionality were satisfied .
sf-36 , 36-item short form survey it is possible to examine whether the number of item categories is appropriate by using the 
 category probability curve ( fig .
1.response category probability curve of physical functioning ) and step calibration ( table 4table 4.step calibration of the response category of physical functioningcategoryresponse rate ( % ) observed average valuestep calibration1212.742300.321.423493.631.42 ) , both of which are integral in rasch analysis . the x - axis of the category 
 probability curve presents the personal latent characteristic of health status and the logit 
 difference of item difficulty , while the y - axis presents the category probability of a 
 specific response category .
step calibration involves presenting the x - axis value of the 
 point that each category curve crosses .
the response rate of category 3 was 49% , which was the 
 highest . from categories 1 to 3 , the observed average value increased gradually from 2.74 
 to 3.63 .
furthermore , for the step calibration , the numerical value of the two points that 
 each of the three category probability curves crossed was shown to increase 
 gradually  specifically , the value between categories 1 and 2 was 1.42 and that between 2 
 and 3 was 1.42 .
2.response category probability curve of role limitation  physical and table 5table 5.step calibration of the response category of role limitation  physicalcategoryresponse rate ( % ) observed average valuestep calibration195.262222.745.113220.401.024313.051.385164.944.75 present the category probability curve and step calibration of the four items 
 of the role limitation
 physical factor , which were answered using a five - point scale . as 
 observed from the figure , the crossing points increased gradually , as follows : between 
 categories 1 and 2 , the crossing point was 5.11 ; between 2 and 3 , it was 1.02 ; between 3 
 and 4 , it was 1.38 ; and between 4 and 5 , it was 4.75 .
3.response category probability curve of role limitation  emotion and table 6table 6.step calibration of the response category of role limitation  emotioncategoryresponse rate ( % ) observed average valuestep calibration155.992173.336.153320.282.194343.972.165125.926.17 show the category probability curve and step calibration of the three items of 
 the role limitation  emotion factor , which were also answered using a five - point scale .
the 
 crossing points increased gradually , as follows : between categories 1 and 2 , the crossing 
 point was 6.15 ; between categories 2 and 3 , it was 2.19 ; between categories 3 and 4 , it 
 was 2.16 ; and between categories 4 and 5 , it was 6.17 .
4.response category probability curve of mental health and table 7table 7.step calibration of the response category of mental healthcategoryresponse rate ( % ) observed average valuestep calibration1111.882140.771.543210.210.654211.250.755322.561.44 show the category probability curve and step calibration of the five items of 
 the mental health factor , which were answered on a five - point scale . as before , the crossing 
 points increased gradually , as follows : between categories 1 and 2 , the crossing point was 
 1.54 ; between categories 2 and 3 , it was 0.65 ; between categories 3 and 4 , it was 0.75 ; 
 and between categories 4 and 5 , it was 1.44 .
5.response category probability curve of vitality and table 8table 8.step calibration of the response category of vitalitycategoryresponse rate ( % ) observed average valuestep calibration1171.992190.951.523240.110.684191.010.745212.051.46 present the category probability curve and step calibration of the four items 
 of the vitality factor , which were answered on a five - point scale .
the crossing points 
 increased gradually , as follows : between categories 1 and 2 , the crossing point was 1.52 ; 
 between categories 2 and 3 , it was 0.68 ; between categories 3 and 4 , it was 0.74 ; and 
 between categories 4 and 5 , it was 1.46 .
6.response category probability curve of general health and table 9table 9.step calibration of the response category of general healthcategoryresponse rate ( % ) observed average valuestep calibration1162.272251.182.173260.110.604231.050.595101.812.18 display the category probability curve and step calibration of the five items 
 of the general health factor , which were answered on a five - point scale .
the crossing point 
 increased gradually , as follows : between categories 1 and 2 , the crossing point was 2.17 ; 
 between categories 2 and 3 , it was 0.60 ; between categories 3 and 4 , it was 0.59 ; and 
 between categories 4 and 5 , it was 2.18 .
physical response category probability curve of role limitation  emotion response category probability curve of mental health response category probability curve of vitality response category probability curve of general health test of goodness - of - fit : next , we examined the item difficulty and the goodness - of - fit of 
 the factors ( table 10table 10.item difficulty and goodness - of - fit indexno.itemscalibration logitse logitinfit mnsqoutfit mnsqphysical functioning1engaging in vigorous activities such as running , lifting heavy 
 objects , or participating in strenuous sports3.680.110.931.962engaging in moderate activities such as moving a table , pushing a 
 vacuum cleaner , bowling , or playing golf1.590.101.061.223able to lift or carry groceries0.090.110.971.034able to climb several flights of stairs1.220.100.760.665able to climb one flight of stairs0.960.111.020.986able to bend , kneel , or stoop0.880.101.431.677able to walk more than a mile0.070.110.880.908able to walk several blocks1.120.120.810.719able to walk one block1.930.130.910.6910able to bathe or dress yourself3.190.161.200.64role limitation  physical1you have to cut down on the amount of time you spend on work or 
 other activities0.600.101.131.142you have accomplished less than you would have liked0.090.101.010.983you are limited in the kind of work or other activities you can 
 perform0.530.100.920.904you have difficulty performing work or other activities ( for 
 example , it takes extra effort)0.160.100.880.85role limitation 
emotion1you have to cut down on the amount of time spent on work or other 
 activities due to feeling depressed or anxious0.270.130.880.862you have accomplished less than you would have liked due to feeling 
 depressed or anxious0.040.130.690.653you
did not do work or other activities as carefully as usual due 
 to feeling depressed or anxious0.230.131.361.32mental health1are you a very nervous person?1.240.071.441.582do you feel so down in the dumps that nothing could cheer you 
 up?0.730.060.780.703do you feel calm and peaceful?1.280.061.051.004do you feel downhearted and blue?0.550.060.880.855are you a happy person?1.240.060.970.92vitality1do you feel full of pep?0.630.060.840.842do you have a lot of energy?0.810.061.041.013do you feel worn out?1.360.061.021.074do you feel tired?0.080.061.101.14general health1 in general , would you say your health is0.990.060.780.742i seem to get sick a little easier than other people do0.940.061.010.993i am as healthy as anybody i know0.150.060.950.904i expect my health to get worse0.220.061.391.465my health is excellent0.120.060.870.82item names are descriptions of the content and do not reflect the exact korean 
 wording of the question .  
the closer the fit index is to 1.0 , the more appropriate 
 the item . in physical functioning ,
the infit and outfit indexes of the first item ( engaging 
 in vigorous activities such as running , lifting heavy objects , or participating in strenuous 
 sports ) were respectively 0.93 and 1.96 ( the latter being over the threshold ) ; those of the 
 fourth item ( climbing several flights of stairs ) were respectively 0.76 and 0.66 ( the latter 
 being below the threshold ) ; those of the sixth item ( being able to bend , kneel , or stoop ) 
 were respectively 1.43 and 1.67 ( both of which were over the threshold ) ; those of the ninth 
 item ( being able to walk one block ) were respectively 0.91 and 0.69 ( the latter being below 
 the threshold ) ; and those of the 10th item ( being able to bathe or dress ) were respectively 
 1.20 and 0.64 ( the latter being below the threshold ) .
for role limitation  emotion , the infit 
 and outfit indexes of the second item ( accomplished less than would have liked due to 
 feeling depressed or anxious ) were respectively 0.69 and 0.65 ( both of which were below the 
 threshold ) , and those of the third item ( did not do work or other activities as carefully as 
 usual due to feeling depressed or anxious ) were respectively 1.36 and 1.32 ( both of which 
 were over the threshold ) . for mental health ,
the infit and outfit indexes of the first item 
 (  are you a very nervous person ?
 ) were respectively 1.44 and 1.58 ( both of which were over 
 the threshold ) .
for general health , the infit and outfit indexes of the fourth item (  i 
 expect my health to get worse  ) were respectively 1.39 and 1.46 ( both of which were over the 
 threshold ) .
the other items , such as the four items of role limitation  physical and the four 
 items of vitality , were appropriate , with goodness - of - fit ( infit and outfit ) indexes over 
 0.70 and under 1.30 .
item names are descriptions of the content and do not reflect the exact korean 
 wording of the question .  
this study examined whether the sf-36 is appropriate for elderly koreans using rasch 
 analysis .
the six factors of the sf-36 were found to satisfy the criterion of 
 unidimensionality .
furthermore , step calibration showed that the three - point scale used to 
 respond to items of the physical functioning factor and the five - point scales for the role 
 limitation  physical , role limitation  emotion , mental health , vitality , and general health 
 factors were appropriate .
this implies that the sf-36 response categories are appropriate 
 for elderly koreans , and that the elderly who participated in this study understood the 
 reverse scored items of the sf-36 . in our study , fewer than three items from each factor
 which tested content - based evidence 
 such as bodily pain , social functioning , and health changes  were excluded from the analysis . 

this corresponds with the results of bollen25 and gilbert et al.26 , the latter of whom conducted a psychometric scaling study , which 
 indicated that at least three items were appropriate for exclusion .
however , the results of 
 the test of goodness - of - fit suggested that five of the ten items in the physical functioning 
 factor are inappropriate .
the infit indexes of items 1 ( engaging in vigorous activities such 
 as running , lifting heavy objects , participating in strenuous sports ) and 6 ( being able to 
 bend , kneel , or stoop ) were over 1.30 .
this implies that these items were incongruent with 
 other items and confused subjects27 , 
 making these items inappropriate for measuring the physical functioning level of elderly 
 koreans .
in addition , the outfit indexes of items 4 ( being able to climb several flights of 
 stairs ) , 9 ( being able to walk one block ) , and 10 ( being able to bathe or dress ) were less 
 than 0.70 .
this suggests that these items overlap with each other , and excluding them would 
 simplify and clarify the measurement28 .
furthermore , items 2 ( accomplished less than you would have liked due to feeling depressed 
 or anxious ) and 3 ( did not do work or other activities as carefully as usual due to feeling 
 depressed or anxious ) of role limitation  emotion , which consists of three items , were found 
 to be inappropriate .
item 2 overlapped with role limitation  physical and item 3 had the 
 highest logit difficulty , which likely means that it was confusing to subjects .
both the 
 infit and outfit indexes of one item each of the role limitation  emotion and general health 
 factors were over 1.30 , making these items completely inappropriate for the participants . 

item 1 in mental health (  are you a very nervous person ?  ) and item 4 in general health (  i 
 expect my health to get worse  ) were incongruent with other items within the same factors ; 
 that is , subjects who scored highly on other items scored low for item 1 in mental health 
 and item 4 in general health .
worse  could have been confusing because it is the only negatively phrased 
 item in the general health factor .
this study investigated the validity of the sf-36 for measuring the health status of 
 elderly koreans by applying the rasch model .
we found that nine items on this scale are 
 inappropriate for measuring the health status of elderly koreans .
therefore , it is necessary 
 to revise this scale to make it better able to measure the health status of elderly koreans . 

future studies should explore ways of improving the validity of the sf-36 for elderly 
 koreans .
 [ purpose ] to verify , using rasch analysis , the applicability of the 36-item short form 
 health survey ( sf-36 ) to elderly koreans , as this instrument would be useful for 
 determining elderly individuals overall performance and providing them with health 
 information . 
 [ subjects and methods ] the sf-36 was administered to a sample of 510 
 individuals aged over 60 living in the seoul and gyeonggi areas of south korea . when 
 testing for goodness - of - fit , we considered items with infit and outfit indexes of over 
 1.30 or less than 0.70 to be incongruent . 
 sf-36 factors that contained over three items , 
 including physical functioning , role limitations ( physical and emotional ) , mental health , 
 vitality , and general health , were analyzed . 
 each factor was examined through step 
 calibration of the response categories in the probability curve . 
 [ results ] the response 
 categories were found to be appropriate because the adjustment values of each factor 
 increased . 
 we found five items in physical functioning , two items in role 
 limitation  emotion , one item in mental health , and one item in general health to be 
 incongruent ; all items in the role limitation  physical and vitality factors were 
 congruent . 
 [ conclusion ] we conclude that the sf-36 could be revised to more accurately 
 measure the health status of elderly koreans . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION