The lecture Biostatistics and Epidemiology Question Set 1 by Lecturio USMLE is from the course Biostatistics and Epidemiology  High Yield Questions.
In a small town, on December 31st, 2013, there were 2000 cases of diabetes mellitus of which 324 were diagnosed with cases of diabetic retinopathy. In 2014, 37 cases developed diabetic retinopathy and 3 of them expired due to myocardial infarction. 47 among them who did not develop diabetic retinopathy also died in the year 2014 due to various cases. 100 new cases each of diabetes mellitus were diagnosed in the years 2013 and 2014. If we assume that there were no emigrations or immigrations, then the point prevalence of diabetic retinopathy on December 31st, 2014 can be calculated if we also know which of the following pieces of information?
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 handwashing 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
In a research work, the association between serum LDL levels and socioeconomic status was studied. Socioeconomic status was coded as High, Medium and Low. The LDL levels variable was tested for its normality using Kolmogorov Smirnov test and the p value of that test came as 0.24. The null hypothesis was formulated as ‘there is no association between serum LDL levels and socioeconomic status’. Which statistical test will you use to disprove this null hypothesis?
A pretest questionnaire was given to a group of 67 students to assess their knowledge before a 3 day workshop on ‘undergraduate biostatistics’. Students were asked not to write their name or register numbers on the questionnaire sheet to maintain anonymity while evaluation. Even code numbers were not used. The questionnaires were filled and returned within 10 minutes. After the three day workshop, the same questionnaire was again given as a posttest. All the posttest questionnaires were collected by 3 organizers and kept separately from the pretest questionnaires. Later, data entry and analysis was done by a different organizer to find out whether the workshop was beneficial to the students. Which parametric statistical test should she use?
The frequencies of different haemoglobin levels of all 1000 medical students in a college were plotted in a graph and a distribution curve was obtained. The mean was 11.2 gm/dl with a standard deviation of 2.1. The median was 11.1 gm/dl and the mode was 11.3 gm/dl. It was decided that all students having a haemoglobin level below 7 gm/dl would be referred to a nearby haematology clinic for expert evaluation and management. Approximately how many students would have been referred?
In a study assessing the relationship between dietary oil intake and serum VLDL of 100 middle aged women belonging to a particular community, it was found that the mean oil intake was 25 ml per day with a standard deviation of 4.3 and the median was 18 ml per day. The data was explored in a statistical software and the p values of normality tests were significant. Serum VLDL levels were found to be normally distributed. The researcher was planning to look for any correlation between these two variables. In this case what advice would you give to him?
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?
A new drug A, which passed safety and efficacy tests was now going to be tested against a drug B for comparison purposes. The doctor who was conducting this study recruited 380 individuals who were willing to take participate in the study. He divided them into two groups of 190 each and he didn’t inform any of the patients which drug they were getting though he was aware of it while giving them the drugs. After the study period, data was analysed and results were obtained. Which study design was used here?
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 710 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 nonsmokers, 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 gastrooesophageal 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,
A researcher was studying the association between haemoglobin value and BMI. He divided the students of a class into two groups based on their BMIs into normal weight group and overweight group. Then he measured the haemoglobin values of all the students. His null hypothesis was that there is no association between haemoglobin value and body weight. The mean haemoglobin value of the normal weight group was 13.4 gm/dl and that of the overweight group was 13.8 gm/dl. He obtained a mean difference of 0.4 gm/dl between the two groups. He did an unpaired t test and he got a p value of 0.10. What does this mean?
In a study to find out the association between smoking and bladder cancer, 100 adult males with bladder cancer were recruited to the study group. The control group consisted of 100 similar individuals without bladder cancer. Their history of smoking was obtained and the data was analysed. The calculated odds ratio was 2.7. What does this mean?
In a study for determining the risk factors of young age myocardial infarction (MI), 30 cases of young age MI were recruited to the study group. 60 suitable individuals were recruited to the control group. Educational status was considered as an important variable as it would affect the awareness about the disease and its risk factors. Education status data was taken qualitatively in four categories and then later recoded to two new categories, namely low education and high education. A chi square test was done to test the significance and the risk was also obtained as Odds ratio of 2.1 for the low education category with a confidence interval of 0.9 to 9.7. What inference do you make on the association between young age myocardial infarction and educational status with this study?
A researcher faced a task of calculating the mean height of the male students in a college having 2000 male students and 1750 female students. The mean height of the sample was obtained as 176 cm with a standard deviation of 7 cm. The researcher calculated a confidence interval for the mean height of the male students in that college. What more do you need to calculate the same?
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