EVALUATION OF PRENATAL-CARE INFORMATION ON BIRTH CERTIFICATES

Misclassification frequently leads to bias in epidemiological studies, and causes concern for perinatal epidemiologists interested in using birth certificates as a data source. We used a maximum likelihood meth od to estimate the classification probabilities (conditional probabili ties that indicate the probability of classification in a particular c ategory, given the person's true category) of two data sources for a t hree-category outcome of prenatal care. The probability that women rec eiving adequate or inadequate care were correctly classified was estim ated to be greater than 90%. The probability was much lower (<35%) tha t women receiving intermediate care were correctly classified. The mis classification of women from the intermediate category resulted in poo r predictive values (<70%) of women classified as receiving either ade quate or inadequate care. Because of these findings, we combined the a dequate and intermediate categories to form a two-category classificat ion system. This revision resulted in higher positive predictive value s (>90%) with only a slightly lower classification probability (>85%) for the combined category. We conclude that the degree of accuracy for a two-category classification of prenatal care based upon birth certi ficate information is acceptable, but we question the accuracy of indi ces of prenatal care with more than two categories.