Question

Pregnant women were recruited during their first trimester to study the relationship between chocolate consumption during pregnancy and risk of preeclampsia (pregnancy-induced hypertension). They were interviewed about chocolate consumption, age, race, education, smoking, body mass index, and previous pregnancy history. Participants were re-interviewed after delivery to obtain information on chocolate consumption during the third trimester of pregnancy. In addition, umbilical cord blood was collected at the time of delivery and measured for concentration of theobromine (the major metabolite of chocolate). Obstetrics records were obtained to determine if preeclampsia developed during the pregnancy. Of 1995 eligible women, 348 were excluded due to preexisting hypertension or preeclampsia at the first study visit, leaving a sample size of 1647 women

(h) Only women who delivered a live birth were included in the analysis. A concern is that exclusion of women who miscarried could cause bias in the study findings.

(h-i) Would this be a type of information bias or selection bias? Explain.

(h-ii) 8% of women enrolled in the study miscarried. Is it likely that the associations observed above are due to bias from excluding these women? Explain.

Answer 1

As per the information provided following points to be noted-

1.They were interviewed about chocolate consumption, age, race, education, smoking, body mass index, and previous pregnancy history.

2.Participants were re-interviewed after delivery to obtain information on chocolate consumption during the third trimester of pregnancy.

3.In addition, umbilical cord blood was collected at the time of delivery and measured for concentration of theobromine (the major metabolite of chocolate) which could have been collected at the time of miscarriage as well

h. Biased is any error resulting from methods used by the investigator to recruit individual for the study,from the factor effecting the study participation (selection bias) or from systematic distortions when collecting information about exposurs and dieseases.

h-i) Hence, only women who delivered a live birth were included in the analysis. A concern is that exclusion of women who miscarried could cause bias in the study findings and such type of sample inclusion will be considered as information bias.

h-ii) 8% of women enrolled in the study miscarried. Is it likely that the associations observed above are due to bias from excluding these women such type of sample inclusion will be considered as selection bias.