Biostatistics Odds Ratio & Relative Risk

A study is done to investigate the role of coffee consumption on the development of colon cancer. One thousand people, half with colon cancer and half without colon cancer, are entered in the study. Of those with colon cancer, 300 people report drinking one glass of coffee per day compared with 400 people in the group without colon cancer. What is the odds ratio? (A) 0.38 (B) 0.64 (C) 0.75 (D) 1.33 (E) 2.67

(A) 0.38 Odds ratio = (300x100)/(400x200) = 30000/80000 = 0.38 Odds ratio is the best statistic for determining disease risk after a particular exposure in case-controlled studies.

A study is conducted to determine the risk of developing asthma in children who grow up in households with smokers. One thousand children are enrolled in the study and followed for 5 years. Four hundred of the children grew up in households with a smoker, and the rest of the children grew up in households without a smoker. At the end of the study, 80 children that grew up in a household with smokers developed asthma, and 40 children that grew up in a household without smokers developed asthma. What is the attributable risk? (A) 0.03 (B) 0.13 (C) 0.27 (D) 2.00 (E) 3.50 (F) 7.50 (G) 30.00

(B) 0.13 Attributable risk is the difference in risk of developing a particular disease in patients with an exposure compared with those without the exposure. Attributable risk= 80/400 - 40/600 = 0.20 - 0.07 = 0.13

A study is conducted to determine the role of exposure to asbestos to the development of lung cancer. One thousand people are recruited for the study, of which half have known exposure to asbestos and half do not have any exposure. The participants are followed for 10 years to determine how many people develop lung cancer. At the end of 10 years, 25% of those that were exposed to asbestos and 1 0% who are not exposed to asbestos drop out of the study. Of those remaining, 100 people who were exposed to asbestos have been diagnosed with lung cancer compared with 50 people who were not exposed. What is the attributable risk? (A) 0.10 (B) 0.16 (C) 2.00 (D) 2.40 (E) 6.25

(B) 0.16 Attributable risk is the difference in risk of developing a particular disease in patients with an exposure compared with those without the exposure. Attributable risk = 100/375 - 50/450 = 0.27 - 0.11 = 0.16

A group of scientists decides to conduct a study addressing the long-term effects of maternal alcohol consumption on their infants after conception. Two hundred women, including those who suffer from alcoholism and those who do not, are recruited into the study when they present for their first primary care visit. A medical history is taken on alcohol use, prenatal care, nutritional status, and smoking behaviors; these are measured monthly during the pregnancy. The researchers follow the women's pregnancies until term, after which they devote their attention to the health and behaviors of the offspring. Which of the following is the most appropriate statistic the researchers will be able to calculate as a result of their study? (A) Attributable risk of offspring abnormalities in mothers who smoke (B) Odds ratio of offspring abnormalities in mothers who consume alcohol during pregnancy (C) Prevalence of alcohol consumption during pregnancy (D) Proportion of all offspring abnormalities that are due to alcohol consumption during pregnancy (E) Relative risk of offspring abnormalities in mothers who consume alcohol during pregnancy

(B) Odds ratio of offspring abnormalities in mothers who consume alcohol during pregnancy A retrospective cohort study includes a group of subjects who had a certain condition or received a certain treatment at some time in the past and compares their outcomes to those of another group (a control group) made up of subjects who did not have this condition or receive the treatment. In this study the risk factor is the presence of diabetes in the mothers and the outcome is LGA babies.

To estimate the relative risk in a case-control study, which of the following is calculated? (A) Attributable risk (B) Odds-risk ratio (C) Incidence rate (D) Prevalence ratio (E) Sensitivity

(B) Odds-risk ratio

An oncologist completes gene analysts of 500 patients of her patients who died of breast cancer. She finds that 20% of these patients have a BRCA mutation. She then assembles a group of 600 autopsy records of patients who died without detectable breast cancer and finds that 5% of them were positive for a BRCA mutation. Based on these data, what is a woman's relative risk for developing breast cancer if she is positive for a BRCA mutation? (A) 0.2 (B) 0.95 (C) 1.9 (D) 4.0 (E) 4.8

(C) 1.9 The relative risk is a measure of increased probability of getting a disease after exposure to a risk factor when compared to unexposed individuals. RR= [100/130] / [400/970] = 1.9 Thus, individuals with the BRCA were almost twice as likely to develop breast cancer than those who did not.

A manufacturing company hires an epidemiologist to study the risk of developing thyroid cancer after exposure to a chemical in their plant. The researcher assembles a group of retired employees who were exposed to the chemical, and a group who were not. He reviews the medical records of all subjects, and those without prior thyroid pathology undergo thyroid biopsy. The researcher determines that the relative risk for developing thyroid cancer after exposure to this chemical is 2.2 with a 95% confidence interval of 0.97 to 3.4. Which of the following is true about the conclusions of this study? (A) 95% of those exposed to the chemical will develop thyroid cancer (B) The chemical is protective against thyroid cancer (C) The standard error of the mean is 1.2 (D) There is no significant increased risk for thyroid cancer after chemical exposure (E) There is significant increased risk for thyroid cancer after chemical exposure

(D) There is no significant increased risk for thyroid cancer after chemical exposure This question asks you to interpret a 95% confidence interval, which, by definition, states that we are 95% certain that the actual value (in this case the relative risk) lies within the given range. Relative risks are calculated to describe the probability of getting a disease after exposure to something (in this case a chemical) in comparison to those who were not exposed. A relative risk of 1 means that there is no difference in the risk of developing the disease between the groups. In this case, since 1 is within the 95% confidence interval, the null hypothesis that there is no difference between those exposed and those not exposed can not be rejected.

A cohort study is conducted to determine the risk of developing lung cancer in patients who smoke cigarettes daily. Two thousand people are initially enrolled, half of which smoke and half who do not. The participants are followed for 20 years. During that time, 25% of the participants who smoke drop out of the study while 20% of those who do not smoke drop out. At the end of the study, 300 people who smoke are diagnosed with lung cancer, compared with 60 people who do not smoke. What is the relative risk of developing lung cancer in patients who smoke? (A) 0.19 (B) 0.24 (C) 0.33 (D) 5.00 (E) 5.33 (F) 8.22

(E) 5.33 Relative risk is the best statistic for determining the risk of disease after a particular exposure in cohort studies. Relative risk = (300/750)/(60/800) = 0.4/0.075 = 5.33

A case-controlled study is conducted to investigate the role of cigarette smoking on the development of chronic obstructive pulmonary disease (COPD). For the study, 500 participants are enrolled, half of which have a history of cigarette smoking. Only 100 participants have a history of COPD, 80 of which are smokers. What are the odds that a patient with COPD will have a history of smoking? (A) 0.47 (B) 0.80 (C) 4.00 (D) 5.41 (E) 8.00 (F) 13.50

(E) 5.33 The relative risk is a good statistic to calculate the probability of getting a particular disease in a group with a particular exposure as compared to those without the exposure. Relative risk = (300/750)/(60/800) = 0.4/0.075 = 5.33

In a cohort study, the ratio of the incidence rate of miscarriage among women who use liquid crystal display (LCD) computer screens to the incidence rate of miscarriage among women who do not use LCD computer screens is the (A) attributable risk (B) odds-risk ratio (C) incidence rate (D) prevalence ratio (E) relative risk

(E) relative risk In a cohort study, the ratio of the incidence rate of a condition (e.g., miscarriage) in exposed people to the incidence rate in non-exposed people is the relative risk.