n below. This demonstrates that the vast majority of results lie on the predicted line. Only a small proportion lie off the line. These represent results which had recalculation of values due to changes in gestation date or other factors. They are clearly few in number so it is valid to conclude that correction of the one Y2K Problem has satisfactorily returned the Sheffield screening program back to its previous position. Figure 3. The remaining part of this report will deal with areas of the Sheffield Down’s screen which I believe ought to be amended immediately within PathLAN to provide confidence that no future errors are missed and secondly, amendments that should be made to the program when any new computer system is installed. Understanding of the issues included here may be aided by the description of how Down’s risk calculations work later in this report.2) Further Problems with the PathLAN software 2a) Age Risk CalculationThe age risk calculation formula used in the Sheffield program is:[Equation 3 - as in PathLAN]Risk (R) = 0.999373 + e(0.286.Age - 16.2395)-----------------------------------------0.000627 + e(0.286.Age - 16.2395)[Equation 3 - restated]Risk (R) = 0.999373 - e(0.286.Age - 16.2395) -----------------------------------------0.000627 + e(0.286.Age - 16.2395)The effect this has on screening is minimal but should be corrected.Table3: Correct & incorrect age risks due to PathLAN bug AgeCorrect Age RiskSheffield Age Risk151577.625501577.64591201528.041021528.12360251350.635421350.9404730909.29654910.1550235383.99492385.5121440111.85583113.714304527.5438329.508044620.5398022.512794715.2365917.216234811.2289113.21358498.2046810.19314505.925077.916392b) Calculation of Median Values & Population ParametersCurrently median values are calculated on a ‘completed week’ basis. I have previously demonstrated this to be an ineffective way to correct for maternal age in some screening programs....
