Estimating dropout effects upon six month weight comparisons between high and low risk infants

Neonates classified as high and low risk for developmental complications were examined in a hospital clinic at six months of age. Among several measures of infant development, weight was selected for a study of dropout effects. At the six month clinic visit, 85 of 193 high risk and 75 of the 194 low risk neonates selected were still in the study. The overall dropout rate was 59%. In order to assess the effect of dropouts upon six month weight comparisons between high and low risk infants, the following three techniques were used to estimate missing weight values: adding specified constants to birthweight, adding random normal numbers to birthweight, and predicting weight by regression equations. Regardless of the estimating technique used, the mean weight of the high risk group was significantly lower than that of the low risk group. Dropouts did not differ significantly from nodropouts in prenatal, intrapartum, or neonatal characteristics. The study results suggested that further comparisons between high and low risk infant groups at six months of age could proceed under the assumption that dropouts would not affect any conclusions drawn from the study.