Indicate the one major type of limitation that is possible in each of the situat
ID: 3314394 • Letter: I
Question
Indicate the one major type of limitation that is possible in each of the situations described below.
Choose from the following: selection bias, information bias, confounding, random error, or no error. Choose only one per example.
1) In a study to determine the incidence of a chronic disease, 150 people were examined at the end of a three-year period. Twelve cases were found, giving a cumulative incidence of 8%. Fifty other members of the initial cohort could not be examined; 20 of these 50 could not be examined because they died.
2) High parity (high number of pregnancies) was once thought to be a risk factor for giving birth to an infant with Down Syndrome, as these infants were most likely to be the third, fourth or even later birth. Maternal age also increases with parity (number of pregnancies). Older mothers are more likely than younger mothers to being giving birth for the third, fourth or fifth time. But when it was also discovered that even older mothers giving birth for the first time had a higher proportion of infants with Down Syndrome than younger mothers, it became clear that high maternal age, not high parity, was the true risk factor for having a Down’s Syndrome baby.
3) Three hundred cases and 600 controls were selected among mothers for a case-control study to see if maternal coffee consumption was related to low birth weight in the mothers' babies. Data were collected on past coffee consumption patterns for the mothers. The overall association between maternal coffee consumption and low birth weight was reported to be strong (Odds Ratio = 3.4). When the data were later reanalyzed in a different study and adjusted for cigarette smoking, however, there was no longer any association between maternal coffee drinking and infant birth weight (Odds Ratio = 1.0). Maternal smoking is a known risk factor for low infant birth weight.
4) In a case-control study of tampon use and menstrual toxic shock syndrome, friends of the cases diagnosed with toxic shock syndrome were recruited as controls. In this study a much weaker association between tampon use and toxic shock syndrome was found by comparison to another study which had used random digit telephone number dialing to recruit controls.
Explanation / Answer
Answer:
1) Selction Bias - occurs when the selection of participants in one group results in a different outcome than the selection for the other group .
2) Random Error - Error made by chance, forget to consider another factor responsible.
3) Confounding - occurs when the observed result between exposure and disease differs from the truth because of the influence of the third variable
4) Information Bias - occurs when information is collected differently between two groups, leading to an error in the conclusion of the association.