THE EFFECT OF SELECTIVE REPORTING ON ESTIMATES OF WEANING WEIGHT PARAMETERS IN BEEF-CATTLE

The effect of selective reporting on estimates of weaning weight param eters in beef cattle was evaluated by comparing REML estimates from un altered and altered simulated data. Selective reporting reduced estima tes of weaning weight direct (WWD), maternal milk (MAT), and error var iances. However, heritability estimates were not greatly affected beca use the reductions in variance estimates were relatively proportionate . When the true value for the direct-maternal (DM) correlation was zer o or negative, selective reporting caused estimates of DM to be less p ositive or more negative in 50 of 62 comparisons, with an average chan ge of -.136. When the true value for DM was positive, selective report ing increased the positive magnitude of DM estimates in 12 of 20 compa risons, with an average change of +.040. In BLUP of unaltered data wit h a true DM value of -.09, using a -.28 and a zero DM correlation redu ced the correlation of MAT EPD with true values .065 and .041, respect ively. These results suggest that the reliability of parameter estimat es (and BLUPs) would be improved by estimating parameters from represe ntative subsets of data free of reporting bias.