Biostatistics Practice Questions

Q: In a UK study, it was found that there were more deaths from Asthma than the sales of Anti-asthma drugs would suggest. This is an example of

Ecological study. ***Ecological study*** - An **ecological study** analyzes data at the population or group level rather than at the individual level. - In this scenario, the comparison of asthma deaths (population-level data) with anti-asthma drug sales (another population-level aggregate) for an entire country (UK) is characteristic of an ecological study. - This represents an **ecological correlation** where aggregate data is used to identify patterns at the population level. *Experimental study* - An **experimental study** involves direct intervention by the researcher to control variables and assign subjects to different groups (e.g., treatment vs. control) to assess cause-and-effect. - This study design does not involve any intervention or randomization; it's an observational analysis of existing population data. *Case-control study* - A **case-control study** compares individuals with a disease (cases) to individuals without the disease (controls) to identify risk factors at the individual level. - The given scenario is not comparing individuals but rather aggregate data from a population. *Cohort study* - A **cohort study** follows a group of individuals (a cohort) over time to observe the incidence of disease or outcomes in relation to specific exposures. - The scenario describes a cross-sectional comparison of population-level data at a specific point or period, not a longitudinal follow-up of individuals.

Q: Mean bone density amongst 2 groups of 50 people each is compared, which would be the best test:

Student t-test. ***Student t-test*** - The **Student's t-test** is the appropriate statistical test for comparing the **means of two independent groups** when the data is continuous and normally distributed. - Bone density is a **continuous variable**, and the scenario involves comparing the mean bone density between two distinct groups. *Fisher exact test* - The **Fisher exact test** is used for analyzing **categorical data** in a 2×2 contingency table, especially when sample sizes are small. - It is not suitable for comparing continuous variables like bone density. *McNemar test* - **McNemar's test** is used to analyze paired nominal data, typically when comparing two related proportions from the same subjects before and after an intervention. - This scenario involves **independent groups**, not paired data. *Chi-square test* - The **chi-square test** is primarily used to compare **categorical variables** to see if there is a significant association between them. - It's not appropriate for comparing the means of continuous data like bone density.

Q: A study was conducted to investigate the relationship between COPD and smoking. Data was collected from government hospital records on COPD cases and cigarette sales records from finance and taxation departments. What is the study design?

Ecological study. ***Ecological study*** - This study uses **aggregate data** (COPD cases from hospital records, cigarette sales from taxation departments) at the population level, not individual data. - It investigates the relationship between exposure (smoking) and outcome (COPD) across different populations or groups. *Cross-sectional study* - A **cross-sectional study** collects data on exposure and outcome at a **single point in time** from individuals, which is not the case here as aggregate data is used. - It describes the prevalence of a disease and exposure in a population, but does not examine the relationship using population-level aggregates. *Operational study* - An **operational study** focuses on evaluating the effectiveness and efficiency of health services or programs in real-world settings. - It typically involves assessing how well interventions are implemented and their impact, rather than investigating the relationship between disease and exposure using aggregate data. *Case-control study* - A **case-control study** compares individuals with a disease (cases) to individuals without the disease (controls) and looks back retrospectively to identify exposures. - This design relies on individual-level data and is not suitable when only population-level aggregate data is available.

Q: For a positively skewed curve, which measure of central tendency is largest?

Mean. ***Mean*** - In a **positively skewed distribution**, the tail of the distribution extends towards higher values, pulling the **mean** in that direction, making it the largest among the three measures of central tendency. - The presence of **outliers** with large values in the tail disproportionately increases the mean. *Mode* - The **mode** represents the most frequently occurring value in the data set. - In a positively skewed distribution, the mode will be located at the **peak of the distribution**, which is typically the smallest value among the three measures of central tendency. *All are equal* - This statement is characteristic of a **perfectly symmetrical distribution** (e.g., a normal distribution), where the **mean, median, and mode** are all equal. - A positively skewed curve is asymmetrical, meaning these measures will not be equal. *Median* - The **median** is the middle value in an ordered data set, dividing the data into two equal halves. - In a positively skewed distribution, the median will be shifted towards the right of the mode but will still be to the left of the mean, meaning it is **smaller than the mean**.

Q: Child Pugh score puts patients into three categories of Score A (<7), Score B (7-9) and Score C (10-15). The following is a type of which scale?

Ordinal. ***Ordinal*** - An **ordinal scale** ranks data with a meaningful order, like the Child-Pugh score categories (A, B, C), but the difference between ranks isn't necessarily equal or precisely quantifiable. - While categories reflect increasing severity, the "distance" between A and B may not be the same as between B and C in a strictly numerical sense. *Nominal* - A **nominal scale** categorizes data without any order or ranking, such as blood types (A, B, AB, O) or gender. - The Child-Pugh score categories have an inherent order of severity (A < B < C), making it more than just nominal. *Quantitative* - **Quantitative scales** involve numerical data that can be measured and calculated. - While the Child-Pugh score is derived from quantitative variables, the final categorical output (A, B, C) doesn't allow for arithmetic operations between the categories themselves. *Continuous* - A **continuous scale** can take any value within a given range, like height or weight, allowing for infinite precision. - The Child-Pugh score categories (A, B, C) are discrete and specific ranges, not allowing for infinitely precise intermediate values.

Q: Most appropriate measure for central tendency when data includes extreme values?

Median. ***Median*** - The **median** is less affected by **extreme values** or **outliers** because it represents the middle value in an ordered dataset. - It provides a more robust measure of central tendency when the data distribution is **skewed**. *Mode* - The **mode** represents the most frequently occurring value in a dataset; it does not account for the magnitude of other values. - While it is not influenced by extreme values, it may not accurately represent the central tendency of a continuous dataset, especially if there are **multiple modes** or if the most frequent value is not central. *Mean* - The **mean** is calculated by summing all values and dividing by the number of values, making it highly susceptible to **extreme values** or **outliers**. - A single very large or very small value can significantly distort the mean, pulling it away from the true center of most data points. *Geometric mean* - The **geometric mean** is primarily used for data that is **multiplicative** in nature or when dealing with rates of change, or positively skewed distributions. - While it can be less sensitive to extreme values than the arithmetic mean for certain types of data, it is not the most appropriate general measure for central tendency when outliers are present without specific multiplicative contexts.

Q: In a vaccine trial, relative risk is 0.2. What is the vaccine efficacy?

80%. ***80%*** - Vaccine efficacy is calculated as **(1 - Relative Risk) x 100%**. Given a relative risk of 0.2, the efficacy is (1 - 0.2) x 100% = **80%**. - This value represents the **proportionate reduction** in disease incidence in the vaccinated group compared to an unvaccinated group. *90%* - This would imply a relative risk of 0.1, as **(1 - 0.1) x 100% = 90%**. - The given relative risk of **0.2** does not correspond to 90% efficacy. *95%* - This would imply a relative risk of 0.05, as **(1 - 0.05) x 100% = 95%**. - The given relative risk of **0.2** does not correspond to 95% efficacy. *20%* - This value directly represents the **Relative Risk (RR)** itself, or an efficacy calculated incorrectly as RR x 100%. - Vaccine efficacy is a measure of reduction from the unvaccinated state, hence it is **1 - RR**.

Q: Hardy-Weinberg equilibrium shows gene frequency p=0.7, q=0.3. What is frequency of heterozygotes?

0.42. ***0.42*** - In **Hardy-Weinberg equilibrium**, the frequency of heterozygotes is given by the formula **2pq**. - Given **p = 0.7** and **q = 0.3**, the frequency of heterozygotes is 2 * 0.7 * 0.3 = **0.42**. *0.09* - This value represents **q²**, which is the frequency of the **homozygous recessive genotype** (0.3 * 0.3 = 0.09). - It does not represent the frequency of heterozygous individuals. *0.49* - This value represents **p²**, which is the frequency of the **homozygous dominant genotype** (0.7 * 0.7 = 0.49). - It does not represent the frequency of heterozygous individuals. *0.21* - This value represents only **pq** (0.7 * 0.3 = 0.21), not the full frequency of heterozygotes which is **2pq**. - The coefficient of 2 is necessary because there are two ways to be heterozygous (one allele from each parent).

Q: Calculate the sensitivity of a screening test: True Positives=80, False Negatives=20, True Negatives=90, False Positives=10

80%. ***80%*** - Sensitivity is calculated as **True Positives / (True Positives + False Negatives)**. In this case, 80 / (80 + 20) = 80/100, which equals 0.8 or 80%. - This metric represents the proportion of **actual positive cases** that are correctly identified by the test. *90%* - This value might represent the **specificity** (True Negatives / (True Negatives + False Positives)) if calculated with the given numbers (90 / (90 + 10) = 90%). - However, the question specifically asks for **sensitivity**, which is a different measure. *85%* - This percentage would be obtained if the total number of true positives and false negatives was 94 (e.g., 80 / 94), which is not the case here. - It does not correspond to the correct formula for **sensitivity** using the provided data. *95%* - This result would occur if the test correctly identified 95 out of 100 actual positive cases (e.g., 95 TP and 5 FN). - The given data of **80 True Positives** and **20 False Negatives** leads to a lower sensitivity.

Question 1

In a UK study, it was found that there were more deaths from Asthma than the sales of Anti-asthma drugs would suggest. This is an example of

Accepted Answer

Ecological study

Answer

Experimental study

Answer

Case-control study

Answer

Cohort study

Question 2

Mean bone density amongst 2 groups of 50 people each is compared, which would be the best test:

Accepted Answer

Student t-test

Answer

McNemar test

Answer

Chi-square test

Answer

Fisher exact test

Question 3

You have diagnosed a patient clinically as having SLE and ordered 6 tests out of which 4 tests have come positive and 2 are negative. Which of the following values are required to determine the probability of SLE at this point?

Accepted Answer

Prior probability of SLE, sensitivity and specificity of each test

Answer

Relative risk of SLE in the patient

Answer

Incidence and prevalence of SLE

Answer

Incidence of SLE and the predictive value of each test

Question 4

A study was conducted to investigate the relationship between COPD and smoking. Data was collected from government hospital records on COPD cases and cigarette sales records from finance and taxation departments. What is the study design?

Accepted Answer

Ecological study

Answer

Cross-sectional study

Answer

Operational study

Answer

Case-control study

Question 5

For a positively skewed curve, which measure of central tendency is largest?

Accepted Answer

Mean

Answer

Mode

Answer

All are equal

Answer

Median

Question 6

Child Pugh score puts patients into three categories of Score A (<7), Score B (7-9) and Score C (10-15). The following is a type of which scale?

Accepted Answer

Ordinal

Answer

Nominal

Answer

Quantitative

Answer

Continuous

Question 7

Most appropriate measure for central tendency when data includes extreme values?

Accepted Answer

Median

Answer

Mode

Answer

Mean

Answer

Geometric mean

Question 8

In a vaccine trial, relative risk is 0.2. What is the vaccine efficacy?

Accepted Answer

80%

Answer

90%

Answer

95%

Answer

20%

Question 9

Hardy-Weinberg equilibrium shows gene frequency p=0.7, q=0.3. What is frequency of heterozygotes?

Accepted Answer

0.42

Answer

0.09

Answer

0.49

Answer

0.21

Question 10

Calculate the sensitivity of a screening test: True Positives=80, False Negatives=20, True Negatives=90, False Positives=10

Accepted Answer

80%

Answer

90%

Answer

85%

Answer

95%

Biostatistics — MCQs

Biostatistics — MCQs

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