The effect of selective reporting on estimates of weaning weight parameters in beef cattle

The effect of selective reporting on estimates of weaning weight parameters in beef cattle was evaluated by comparing REML estimates from unaltered and altered simulated data. Selective reporting reduced estimates of weaning weight direct (WWD), maternal milk (MAT), and error variances. However, heritability estimates were not greatly affected because the reductions in variance estimates were relatively proportionate. When the true value for the direct-maternal (DM) correlation was zero or negative, selective reporting caused estimates of DM to be less positive or more negative in 50 of 62 comparisons, with an average change of -.136. When the true value for DM was positive, selective reporting increased the positive magnitude of DM estimates in 12 of 20 comparisons, with an average change of +.040. In BLUP of unaltered data with a true DM value of -.09, using a -.28 and a zero DM correlation reduced the correlation of MAT EPD with true values .065 and .041, respectively. These results suggest that the reliability of parameter estimates (and BLUPs) would be improved by estimating parameters from representative subsets of data free of reporting bias.