A prospective cohort study was conducted to determine the risk of heart attack among men with varying levels of baldness.
Indicate the one major type of limitation that is possible in each of the situations described below. Choose from the following, Choose only one per example:
random error
limited generalizability
selection bias
information bias
confounding
A prospective cohort study was conducted to determine the risk of heart attack among men with varying levels of baldness. Third-year residents in dermatology conducted visual baldness assessments at the start of the study (which was before any heart attacks had occurred). Four levels of baldness were coded according to standard procedures: none, minimal, moderate, and severe. The follow up rate was close to 100%. It was later determined that degree of baldness was associated with age, and that age was a risk factor for heart attack.
An epidemiologist reported the following conclusion from a large randomized controlled trial during a national meeting: “Daily use of 500 milligrams of vitamin C for a period of one year is associated with a reduced frequency of upper respiratory infections in children under 10 years of age.” Here are the results: Relative Risk = 0.9, 95% CI = 0.6 – 1.6.
The interviewer doesn’t ask the questions which he is instructed to ask or asks them incorrectly.
This sample only included heterosexual partners who were legally married. The results, although valid for this population, could not necessarily be applied to cohabiting couples who had not gotten married, or to homosexual couples.
Results of a study were published announcing that coffee drinking was a risk factor for bladder cancer. However, it was later noted that coffee drinkers were much more likely to smoke than non-coffee drinkers, and that smoking is a risk factor for bladder cancer. When multivariate analyses were done, adjusting for smoking, coffee drinking and bladder cancer were no longer associated.
Participants in the study were asked if they had ever been diagnosed by a doctor with diabetes. This was used to indicate whether they had diabetes or not.
In a large cohort study of IV drug use and risk of sexually transmitted diseases (STDs), one third of the sample was lost to follow-up over the first five years of the study. Those who dropped out of the study tended to be more likely to have used IV drugs than those who remained in the study, and it was probable that they were also more likely to have become infected with STDs.
High parity (high number of pregnancies) was once thought to be a risk factor for giving birth to an infant with Down Syndrome. It was noticed that infants with Down Syndrome were more likely to be a later birth than the first born. Maternal age also increases with parity. Older mothers are more likely than younger mothers to be 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 Syndrome baby.
The authors of a cross-sectional study hypothesized that lack of regular exercise is associated with obesity in children. Their study of 12 children in Michigan, however, failed to show a statistically significant association between exercise habits and obesity (Prevalence Ratio = 1.9, p = 0.11).
A study to assess the association of diabetes and smoking compared a group of hospitalized individuals with diabetes (cases) with a group of volunteer individuals without diabetes (controls) who were full-time employees of the same hospital where the cases were identified. The results from this study reported, for the first time in the literature, a strong association between diabetes and smoking.
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 and on cigarette smoking, a known risk factor for low birth weight. 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 and adjusted for cigarette smoking, however, there was no longer any association between maternal coffee drinking and infant birth weight (Odds Ratio = 1.0).
A case-control study is conducted to determine the association between alcohol use and fatal automobile crashes. Fatalities (cases) are compared with living controls. Blood samples are always taken from the cases by the forensic service in order to chemically ascertain blood-alcohol content. However, data on drinking was gathered from controls via interview.
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.
Most large prospective cohort studies of heart disease in the 1950s, 60s and 70s focused solely on white males. The results, although valid for white males, could not necessarily be applied to non-whites or females.
A prospective cohort study followed 8,542 women for 10 years to determine if alcohol consumption increased the risk of breast cancer. No significant association was found. Twelve thousand women had been enrolled in the study at its initiation, but 3,458 had withdrawn during the 10-year period. A follow-up sample of spouses, friends, and relatives of the women who withdrew revealed that more than 60% of them had developed breast cancer and that nearly 84% were regular drinkers.
A survey was conducted of sexually transmitted infections based entirely on self-reporting.
The mothers of infants in a case-control study with neural tube defects had better recall of periods of fever during their pregnancies than did mothers of infants without birth defects.
A large epidemiologic study found that elderly adults with dementia were more likely to develop liver cancer than those without dementia. The investigators, however, could offer no plausible biological explanation for the association between dementia and liver cancer. Many of the participants reported heavy drinking, however.
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