Appendix 7: Radiology indicator summary measures Bias the bias is the difference between observed NT measurements and we would expect – from the FMF curve. For example, the expected NT measurement for a CRL of 60mm is 1.65mm. If a fetus with a CRL measurement of 60mm has an NT measurement of 2mm, the difference is 0.35mm 2mm 1.65mm = 0.35mm – Or if the measured NT is 1mm, the difference is -0.65mm 1mm 1.65mm = – ‐0.65mm The figures shown in the distribution plot are the number and percentage of measurements above and below the FMF curve. Spread the spread of NT measurements is the way most measurements will cluster the – FMF curve. The number shown is the factor by which the spread is increased (the measurements vary more greatly than would be expected given the CRL) or decreased (the measurements cluster very tightly around the curve, without the expected normal variance). Trend the curve of observed NT /CRL values should mimic the FMF curve in shape and – direction. The value displayed shows the degree of discrepancy between the expected trend and the observed measurements.
Appendix 7: Radiology indicator summary measures Bias – the bias is the difference between observed NT measurements and we would expect from the FMF curve. For example, the expected NT measurement for a CRL of 60mm is 1.65mm. If a fetus with a CRL measurement of 60mm has an NT measurement of 2mm, the difference is 0.35mm 2mm – 1.65mm = 0.35mm Or if the measured NT is 1mm, the difference is -0.65mm 1mm – 1.65mm = ‐0.65mm The figures shown in the distribution plot are the number and percentage of measurements above and below the FMF curve. Spread – the spread of NT measurements is the way most measurements will cluster the FMF curve. The number shown is the factor by which the spread is increased (the measurements vary more greatly than would be expected given the CRL) or decreased (the measurements cluster very tightly around the curve, without the expected normal variance). Trend – the curve of observed NT /CRL values should mimic the FMF curve in shape and direction. The value displayed shows the degree of discrepancy between the expected trend and the observed measurements.
antenatal-screening-down-syndrome-other-conditions-monitoring-jan2011-dec2015-may17.docx