Biostatistics Practice Questions

Q: By which one of the following studies can relative risk be best calculated?

Cohort study. ***Cohort study*** - A cohort study directly follows groups of individuals (cohorts) over time to observe the **incidence of disease** in exposed versus unexposed groups. - This design allows for the direct calculation of **absolute risks** in each group, from which the **relative risk** can be easily derived. *Correlation study* - A correlation study examines the **relationship between variables** in a population, often using aggregated data, but does not follow individuals over time to assess incidence. - It can identify associations between exposures and outcomes but cannot calculate relative risk directly because it does not provide individual risk data. *Case-control study* - A case-control study compares individuals with a disease (cases) to individuals without the disease (controls) and looks back in time to determine past exposures. - While it can estimate the **odds ratio**, which approximates relative risk when the disease is rare, it cannot directly calculate relative risk because it does not provide the incidence of the disease in exposed versus unexposed populations. *Randomised control trial* - A randomized controlled trial (RCT) is an experimental study where participants are randomly assigned to an intervention or control group to assess the efficacy of an intervention. - While RCTs can calculate relative risk, they are primarily designed to establish **causality** and intervention effectiveness, not to investigate risk factors in naturally occurring populations in the same way a cohort study does for epidemiological insight.

Q: Which of the following types of study designs will be most appropriate to find out the association between mobile phone radiation exposure and cancer?

Case-control. ***Case-control*** - **Among the given options**, case-control studies are most appropriate for investigating the association between mobile phone radiation exposure and cancer. - **Case-control studies** are efficient for investigating rare outcomes like cancer, by comparing exposure histories between individuals with the disease (cases) and those without (controls). - This design allows for studying factors potentially linked to disease despite **long latency periods**. - However, note that **cohort studies** would be even more ideal for this research question as they better establish temporal relationships and minimize recall bias, which is why major studies like the INTERPHONE study used cohort designs. But cohort studies are not among the options provided. *Cross-sectional* - **Cross-sectional studies** assess exposure and outcome simultaneously, making it difficult to establish temporal relationship or causation. - They are suitable for estimating prevalence but not for investigating etiology of diseases with long latency periods like cancer. *Case-series* - A **case series** describes characteristics of a group of patients with a particular disease, but lacks a comparison group. - It cannot establish an association between exposure and outcome, as there is no control for confounding factors. *Single-arm interventional* - A **single-arm interventional study** involves administering an intervention to a single group and observing the outcome, primarily for evaluating efficacy or safety of new treatments. - It is not designed to investigate associations between environmental exposures (like mobile phone radiation) and disease, as it lacks a control group and focuses on interventions rather than observational epidemiology.

Q: A cohort study was conducted among 200 men aged 20–30 years in Rampur village. Out of 200, 120 men were tobacco users and rest 80 didn’t take any form of tobacco. At the end of one year, 40 men among tobacco users and 10 men among non-tobacco users developed tuberculosis. The incidence of tuberculosis among tobacco users is:

33.3 per 100 men/ year. ***33.3 per 100 men/year*** - **Incidence of tuberculosis among tobacco users** is calculated as (Number of new cases among tobacco users / Total number of tobacco users) × 100. - In this study, (40 / 120) × 100 = **33.3 per 100 men/year**. - This is the correct application of the **incidence rate formula** for the exposed group. *30.0 per 100 men/year* - This figure does not correspond to any standard epidemiological calculation for this study. - It may result from mathematical error or confusion with other rates. - The correct calculation for tobacco users yields 33.3, not 30.0. *12.5 per 100 men/year* - This value represents the **incidence among non-tobacco users** (10/80 × 100 = 12.5). - This answers a different question - the incidence in the unexposed group. - The question specifically asks for incidence among **tobacco users**, not non-users. *25.0 per 100 men/year* - This represents the **overall incidence** in the entire cohort: (40 + 10) / (120 + 80) × 100 = 50/200 × 100 = 25.0. - This is the total population incidence, not specific to tobacco users. - The question asks for incidence among tobacco users specifically, which requires using tobacco users as the denominator.

Q: What is the sensitivity of EEG for detecting brain tumours as per the information given below?

90%. ***90%*** - Sensitivity is calculated as **True Positives / (True Positives + False Negatives)**. - Based on the table provided, among patients with brain tumors (disease positive), 36 cases were correctly identified by EEG and 4 cases were missed. - Sensitivity = 36/(36+4) = 36/40 = 0.9 or **90%**. - This indicates that the EEG test correctly identifies 90% of patients who actually have brain tumors. - High sensitivity is important for screening tests to minimize false negatives. *99.99%* - This extremely high percentage is incorrect and not supported by the data. - It would indicate near-perfect detection of all brain tumor cases, which contradicts the table showing 4 missed cases out of 40. - Results from miscalculation or misinterpretation of the sensitivity formula. *0.07%* - This extremely low value represents a fundamental calculation error. - Such low sensitivity would indicate the test is essentially useless for detecting brain tumors. - Does not correspond to any reasonable interpretation of the given data. *85%* - While close to the correct answer, this is mathematically incorrect. - Likely results from calculation error or rounding mistakes. - The correct calculation (36/40) yields exactly 90%, not 85%.

Q: What is the attributable risk percent (etiologic fraction) of tobacco for developing tuberculosis as per the information given below? Tobacco users Tuberculosis Total Present Absent Yes 40 80 120 No 10 70 80 Total 50 150 200

62.5%. ***62.5%*** - The **risk of TB in tobacco users** is 40/120 = 0.333 (33.3%). The **risk of TB in non-tobacco users** is 10/80 = 0.125 (12.5%). - The **attributable risk (AR)** is calculated as: Risk in exposed – Risk in unexposed = 0.333 - 0.125 = 0.208 - The **attributable risk percent (AR%)** or **etiologic fraction** is: [(Risk in exposed – Risk in unexposed) / Risk in exposed] × 100 - AR% = (0.208 / 0.333) × 100 = **62.5%** - This represents the **proportion of disease in the exposed group that can be attributed to the exposure** (tobacco use). *70.6%* - This value does not result from the correct attributable risk percent formula using the provided data. - This might arise from incorrectly calculating the population attributable risk or from computational errors. *50.5%* - This percentage does not result from the appropriate calculation of attributable risk percent. - This may result from calculation errors or misapplication of the formula components. *80.6%* - This value is inconsistent with the correct calculation based on the given data. - This could result from using incorrect ratios or misunderstanding which values belong in the formula.

Q: What is the relative risk of developing tuberculosis among tobacco users as per the information given below?

2.67. **2.67** - To calculate the **relative risk**, we first need to determine the incidence Proportion (IP) of TB in tobacco users and non-tobacco users. - **IP for tobacco users** = (Number of tobacco users with TB) / (Total number of tobacco users) = 40/120 = 0.33. - **IP for non-tobacco users** = (Number of non-tobacco users with TB) / (Total number of non-tobacco users) = 10/80 = 0.125. - **Relative Risk** (RR) = IP of exposed / IP of unexposed = 0.33 / 0.125 = 2.67. *3.90* - This value would be obtained if there was an error in calculating the incidence proportions or the division. - For example, if the calculation for the incidence proportion of non-tobacco users was incorrect. *0.48* - A relative risk value less than 1 would indicate that tobacco use is a **protective factor** against tuberculosis, meaning tobacco users are less likely to develop TB than non-users, which is not the case here. - This value might be obtained by inverting the relative risk calculation (**IP unexposed / IP exposed**). *1.33* - This value is significantly lower than the correct relative risk and would likely result from a miscalculation in the number of cases or total populations for either group. - For instance, if the incidence rate for tobacco users was underestimated or for non-tobacco users was overestimated.

Q: Which one of the following experiments/trials is a part of non-randomized trials?

Uncontrolled trial. ***Uncontrolled trial*** - An **uncontrolled trial** is a single-arm study where all participants receive the same intervention without any control group for comparison. - These are classified as **non-randomized trials** because there is no random allocation between groups (as there is only one group). - Common in early phase drug studies or when ethical considerations prevent withholding treatment. *Before and after comparison studies* - While these are **non-randomized designs**, they are typically classified as **quasi-experimental studies** rather than trials in strict epidemiological terminology. - They measure outcomes in the same population before and after an intervention without random allocation. *Natural experiment* - A **natural experiment** is an **observational study design**, not an experimental trial. - Researchers observe the effects of naturally occurring events or policy changes without any deliberate intervention or random assignment by the investigator. - Example: Comparing health outcomes before and after a public health policy change. *Risk factor trial* - This term is **not standard epidemiological terminology** for trial classification. - Trials are typically classified by design (randomized vs non-randomized) and control status (controlled vs uncontrolled), not by whether they study risk factors. - Most risk factor research uses observational cohort or case-control studies, not trials.

Q: A study was conducted to evaluate the effectiveness of a new antidiabetic drug. The fasting blood glucose levels (mg/dL) of 5 diabetic patients after 3 months of treatment were: 110, 94, 102, 98, 96. Consider the following statements about this data: 1. The range of blood glucose levels is 16 mg/dL 2. The median blood glucose level is 98 mg/dL 3. The standard deviation is √10 mg/dL

1 and 2 only. ***1 and 2 only*** - **Statement 1 is correct**: The **range** is calculated as maximum value minus minimum value. Ordering the data: 94, 96, 98, 102, 110 mg/dL. Range = 110 - 94 = **16 mg/dL** ✓ - **Statement 2 is correct**: For the ordered dataset (94, 96, 98, 102, 110), with n=5 observations, the **median** is the middle (3rd) value = **98 mg/dL** ✓ - **Statement 3 is incorrect**: To calculate standard deviation: - Mean (x̄) = (110 + 94 + 102 + 98 + 96) / 5 = **100 mg/dL** - Deviations from mean: 10, -6, 2, -2, -4 - Sum of squared deviations: 100 + 36 + 4 + 4 + 16 = **160** - Sample variance = 160 / (n-1) = 160 / 4 = **40** - Standard deviation = √40 = **2√10 ≈ 6.32 mg/dL** (NOT √10 ≈ 3.16 mg/dL) ✗ *1, 2 and 3* - This would only be correct if all three statements were true. However, **statement 3 is incorrect** as the actual standard deviation is √40 (or 2√10), not √10. *1 and 3 only* - This is incorrect because **statement 3 is false** (SD = √40, not √10), while statement 2 is actually correct. *2 and 3 only* - This is incorrect because **statement 1 is correct** (range is indeed 16 mg/dL) and **statement 3 is incorrect** (SD ≠ √10).

Q: A new test was developed for detection of COVID-19. What is the sensitivity of the test as per the information provided above?

37.5%. ***37.5%*** - **Sensitivity** is calculated as the number of **true positives** divided by the sum of true positives and false negatives (i.e., total number of individuals with the disease). - From the table, **True Positives (Test Positive and Disease +)** = 60, and **False Negatives (Test Negative and Disease +)** = 100. So, sensitivity = 60 / (60 + 100) = 60 / 160 = 0.375 or 37.5%. *97%* - This value is incorrect. It might be confused with **Negative Predictive Value (NPV)**, which is the probability that subjects with a negative test truly don't have the disease (1800/1900 ≈ 0.947 or 94.7%), but it's not 97%. - It does not correctly represent the calculation for sensitivity as described above. *20.5%* - This value is incorrect. It does not correspond to any standard epidemiological measure of test performance based on the provided data. - This percentage might arise from an incorrect division or addition of values from the table. *60%* - This value is incorrect. While 60 **true positives** are present, sensitivity requires dividing this by the total number of diseased individuals, not just any other total. - This could be confused with the ratio of true positives to total positive tests (Positive Predictive Value), which would be 60/100, resulting in 60%, but this is not sensitivity.

Question 1

By which one of the following studies can relative risk be best calculated?

Accepted Answer

Cohort study

Answer

Correlation study

Answer

Case-control study

Answer

Randomised control trial

Question 2

Which of the following types of study designs will be most appropriate to find out the association between mobile phone radiation exposure and cancer?

Accepted Answer

Case-control

Answer

Cross-sectional

Answer

Case-series

Answer

Single-arm interventional

Question 3

A cohort study was conducted among 200 men aged 20–30 years in Rampur village. Out of 200, 120 men were tobacco users and rest 80 didn’t take any form of tobacco. At the end of one year, 40 men among tobacco users and 10 men among non-tobacco users developed tuberculosis. The incidence of tuberculosis among tobacco users is:

Accepted Answer

33.3 per 100 men/ year

Answer

30.0 per 100 men/ year

Answer

12.5 per 100 men/ year

Answer

25.0 per 100 men / year

Question 4

What is the sensitivity of EEG for detecting brain tumours as per the information given below?

Accepted Answer

90%

Answer

99.99%

Answer

0.07%

Answer

85%

Question 5

What is the attributable risk percent (etiologic fraction) of tobacco for developing tuberculosis as per the information given below? Tobacco users Tuberculosis Total Present Absent Yes 40 80 120 No 10 70 80 Total 50 150 200

Accepted Answer

62.5%

Answer

70.6%

Answer

50.5%

Answer

80.6%

Question 6

What is the relative risk of developing tuberculosis among tobacco users as per the information given below?

Accepted Answer

2.67

Answer

3.90

Answer

0.48

Answer

1.33

Question 7

Which one of the following experiments/trials is a part of non-randomized trials?

Accepted Answer

Uncontrolled trial

Answer

Before and after comparison studies

Answer

Natural experiment

Answer

Risk factor trial

Question 8

Which one of the following statements regarding predictive value of a positive test is true?

Accepted Answer

It tells the probability that a patient with positive test has the disease in question

Answer

It does not tell about diagnostic power of test

Answer

The more prevalent the disease, the less accurate the test is

Answer

It tells the probability that a patient with positive test does not have the disease in question

Question 9

A study was conducted to evaluate the effectiveness of a new antidiabetic drug. The fasting blood glucose levels (mg/dL) of 5 diabetic patients after 3 months of treatment were: 110, 94, 102, 98, 96.

Consider the following statements about this data:

1. The range of blood glucose levels is 16 mg/dL
2. The median blood glucose level is 98 mg/dL  
3. The standard deviation is √10 mg/dL

Accepted Answer

1 and 2 only

Answer

1, 2 and 3

Answer

1 and 3 only

Answer

2 and 3 only

Question 10

A new test was developed for detection of COVID-19. What is the sensitivity of the test as per the information provided above?

Accepted Answer

37.5%

Answer

97%

Answer

20.5%

Answer

60%

Biostatistics — MCQs

Biostatistics — MCQs

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