44: False positive rate for trisomy 21, January 2011 to December 2015 Year False positives True negatives positive rate 2011 38,075 0.03 993 1,049 39,477 0.03 2012 972 39,626 0.02 2013 1,042 40,587 0.03 2014 2015 1,045 41,060 0.02 Table 45: False positive rate for trisomy 18 and 13, January 2011 to December 2015 Year positives True negatives False positive rate 2011 38,995 0.003 127 148 40,441 0.004 2012 150 40,538 0.004 2013 144 41,550 0.003 2014 2015 149 42,025 0.004 False positive rate for screening for trisomy 21 by age, ethnicity and deprivation positive rates by age, ethnicity and NZ deprivation quintile are shown in Table 46. The false positive rate for trisomy 21 increases with age. For example, the false positive rate for women under 20 years in 2015 was 0.01 (1%) compared with 0.32 (32%) for women 45 years and older. This difference is due to the inclusion of prior risk (age) in the calculation. Older women are more likely to have a positive test and are also more likely to have a higher detection rate. This difference has been consistent over time. Table 46: False positive rate for trisomy 21 by age, aggregated January 2011 to December 2015 Age group 2011 2012 2013 2014 2015 Under 20 years 0.01 0.01 0.00 0.01 0.01 20 24 years 0.01 0.01 0.01 0.01 0.01 – 25 29 years 0.01 0.01 0.01 0.01 0.01 – 30 34 years 0.02 0.02 0.02 0.02 0.02 – 35 39 0.05 0.05 0.05 0.05 0.05 – 40 44 0.16 0.16 0.15 0.15 0.18 – 45 and over 0.33 0.33 0.37 0.31 0.27 The false positive rate for 2015 varied across ethnic groups from 0.02 (2%) for Māori and Other to 0.04 (4%) for Pacific. These rates are consistent with previous years.
44: False positive rate for trisomy 21, January 2011 to December 2015 Year False positives True negatives positive rate 2011 993 38,075 0.03 2012 1,049 39,477 0.03 2013 972 39,626 0.02 2014 1,042 40,587 0.03 2015 1,045 41,060 0.02 Table 45: False positive rate for trisomy 18 and 13, January 2011 to December 2015 Year positives True negatives False positive rate 2011 127 38,995 0.003 2012 148 40,441 0.004 2013 150 40,538 0.004 2014 144 41,550 0.003 2015 149 42,025 0.004 False positive rate for screening for trisomy 21 by age, ethnicity and deprivation positive rates by age, ethnicity and NZ deprivation quintile are shown in Table 46. The false positive rate for trisomy 21 increases with age. For example, the false positive rate for women under 20 years in 2015 was 0.01 (1%) compared with 0.32 (32%) for women 45 years and older. This difference is due to the inclusion of prior risk (age) in the calculation. Older women are more likely to have a positive test and are also more likely to have a higher detection rate. This difference has been consistent over time. Table 46: False positive rate for trisomy 21 by age, aggregated January 2011 to December 2015 Age group 2011 2012 2013 2014 2015 Under 20 years 0.01 0.01 0.00 0.01 0.01 20 – 24 years 0.01 0.01 0.01 0.01 0.01 25 – 29 years 0.01 0.01 0.01 0.01 0.01 30 – 34 years 0.02 0.02 0.02 0.02 0.02 35 – 39 0.05 0.05 0.05 0.05 0.05 40 – 44 0.16 0.16 0.15 0.15 0.18 45 and over 0.33 0.33 0.37 0.31 0.27 The false positive rate for 2015 varied across ethnic groups from 0.02 (2%) for Māori and Other to 0.04 (4%) for Pacific. These rates are consistent with previous years.