Biostatistics and Epidemiology Question Set 1

In a population where the prevalence of hepatitis B was 4%, a new screening test was performed to detect the cases as the first round of a research project. The screening test had a sensitivity of 99% and a specificity of 77%. The same test was later used in a high risk group for identifying the cases for the second round of the same research project. The prevalence of hepatitis B in this high risk group was 29%. Which of the following statements is true?

A study was conducted in a hospital to estimate the prevalence of hand-washing among health care personnel. All the study participants were informed that the study duration is one month and the method employed would be a passive observation of their daily routine at the hospital. Out of 127 health care personnel in the hospital, only 89 gave consent for the study and so they were followed up for one month. This study could mostly suffer from

The association between smoking and dementia was proposed as a hypothesis by a researcher. During literature review he found out that it might require more than 20 years of follow up to arrive at valid conclusions. He wanted to finish the study within one year but he was not ready to sacrifice the temporality of exposure and outcome. Assuming there were no other feasibility issues, which study design would best suit his requirements?

A researcher wanted to study about the carcinogenic effects of a food additive. From the literature he found that around 7 different types of cancer were suspected to occur due to the consumption of this food additive. He wanted to study all the possible 7 outcomes. He conducted interviews with a couple of his potential study subjects and discovered that the awareness about this food additive was very low among them though they were consuming it regularly through various foods. Which study design would best suit this researcher?

In a community of population 5000, 40 people of 40 different households developed an infection with a new strain of influenza virus having an incubation period of 7-10 days. The total number of people in these 40 households were 150. Ten days later, 90 new cases of the same disease were reported from these households. Twenty five more cases were reported from these households after a month. Total number of cases reported after one month from this community was 1024. The secondary attack rate is what?

In a study 1000 smokers were followed up for development of emphysema and 200 cases were picked up. In the control group of 1000 non-smokers, 20 people developed emphysema. The total population was 225,000 and the prevalence of smoking in the general population was 40%. The researcher calculated all possible risk estimates including odd’s ratio. How much would be the attributable risk?

In a diagnostic test evaluation of a new imaging modality for detecting salivary gland tumours, the test picked up 90 positives out of the 100 cases that gave a positive result with the gold standard. Out of the 100 negative results with the gold standard, 80 were said to be negative by the test. It was calculated that of the 110 positive results given by the test, 20 were false positive whereas only 10 were false negative. What is the positive likelihood ratio for this test?

In a small town of population 10000, the prevalence of alcohol use was estimated to be 30%. A study was done with a null hypothesis that there is no association between alcohol use and gastro-oesophageal reflux disease (GERD). Of the 200 alcoholics who were followed up, 30 developed GERD and out of the 400 non- alcoholics, 30 developed GERD. What fraction of GERD can be prevented in the general population if alcohol is no longer consumed in this town?

A clinical trial was done to test the efficacy of a new drug ‘alpha’ to treat tinea versicolor. 500 subjects were recruited for this study and were randomized into two groups in equal numbers. Group 1 was given alpha and group 2 were given the conventional antifungal therapy. After the specified intervention, 210 from the study group and 220 from the control group reported back. 190 from the study group and 165 from the control group were cured. What is the number needed to treat of the new drug?

A doctor arrived at a hypothesis that low birth weight is related with obesity later in life. He conducted a study at 95% significance level to disprove his null hypothesis and he got a p value of 0.049. He rejected his null hypothesis and concluded that low birth weight is associated with obesity. In this study,