Biostatistics Practice Questions

Q: A total of 5000 patients with glaucoma are identified and surveyed regarding family history of glaucoma. What is this study design called?

Case series report. ### Explanation **1. Why Case Series Report is Correct:** A **Case Series** is a descriptive study design that describes a group of individuals with a common characteristic (in this case, 5,000 patients with glaucoma). The study simply observes and describes the distribution of a variable (family history) within this specific group. * **Key Identifier:** There is **no comparison group** (no control group of people without glaucoma). Since the researcher is only looking at "cases" to identify patterns or generate hypotheses, it is a case series. **2. Why the Other Options are Incorrect:** * **B. Case-control study:** This requires two groups: Cases (with glaucoma) and Controls (without glaucoma). The study would then compare the frequency of family history between these two groups to calculate an Odds Ratio. * **C. Clinical trial:** This is an experimental study where an intervention (like a new drug) is applied to one group and compared against a placebo or standard treatment. * **D. Cohort study:** This starts with a group of exposed and unexposed individuals (e.g., those with and without family history) and follows them forward in time to see who develops glaucoma. It measures incidence and Relative Risk. **3. NEET-PG High-Yield Pearls:** * **Descriptive vs. Analytical:** Case reports and case series are *descriptive* (generate hypotheses). Case-control and cohort studies are *analytical* (test hypotheses). * **The "No Control" Rule:** If a question describes a large number of patients with a disease but mentions no comparison group, the answer is almost always a **Case Series**. * **Hierarchy of Evidence:** Case series are low on the evidence pyramid because they cannot prove a causal association due to the lack of a control group.

Q: The prevalence of diabetes mellitus in a population was found to be 10 percent. What is the probability that three people selected at random from the population have the disease?

0.001. ### Explanation **1. Understanding the Correct Answer (B: 0.001)** This question tests the application of the **Multiplication Rule of Probability** for independent events. * **Prevalence (P):** 10% or 0.1. This represents the probability that any single individual selected at random has diabetes. * **Independence:** Since the individuals are selected at random from a large population, the health status of one person does not influence the status of the next. * **Calculation:** To find the probability of multiple independent events occurring together (Person 1 AND Person 2 AND Person 3), we multiply their individual probabilities: * $0.1 \times 0.1 \times 0.1 = 0.001$ (or $10^{-3}$). **2. Analysis of Incorrect Options** * **Option A (0.003):** This is a common error where the student **adds** the probabilities ($0.1 + 0.1 + 0.1 = 0.3$) and misplaces the decimal, or confuses the multiplication rule with simple addition. * **Option C (0.03):** This represents $0.1 \times 0.3$, which has no mathematical basis in this scenario. * **Option D (0.01):** This is the probability of only **two** people having the disease ($0.1 \times 0.1$). **3. High-Yield Clinical Pearls for NEET-PG** * **Addition Rule:** Used for "Either/Or" scenarios (mutually exclusive events). E.g., Probability of being Blood Group A OR B. * **Multiplication Rule:** Used for "And" scenarios (independent events). E.g., Probability of two siblings both having an autosomal recessive disorder ($1/4 \times 1/4 = 1/16$). * **Prevalence vs. Incidence:** Remember that Prevalence = Incidence × Mean Duration of disease ($P = I \times D$). In this question, prevalence is used as the "pre-test probability" for random selection. * **Complementary Probability:** The probability of a person *not* having diabetes is $1 - 0.1 = 0.9$. The probability that *none* of the three have the disease would be $0.9^3 = 0.729$.

Q: Calculate the median from the following values: 1.9, 1.9, 1.9, 2.1, 2.4, 2.5, 2.5, 2.9?

2.25. ### Explanation **1. Understanding the Correct Answer (C: 2.25)** The **Median** is the middle-most value in a data set when arranged in ascending or descending order. It is a measure of central tendency that is less affected by extreme values (outliers) compared to the Mean. To calculate the median: * **Step 1: Arrange the data.** The values are already provided in ascending order: 1.9, 1.9, 1.9, 2.1, 2.4, 2.5, 2.5, 2.9. * **Step 2: Count the number of observations ($n$).** Here, $n = 8$. * **Step 3: Apply the formula.** Since $n$ is **even**, the median is the average of the two middle terms ($\frac{n}{2}$ and $\frac{n}{2} + 1$). * The 4th term is **2.1**. * The 5th term is **2.4**. * $\text{Median} = \frac{2.1 + 2.4}{2} = \frac{4.5}{2} = \mathbf{2.25}$. **2. Analysis of Incorrect Options** * **A (1.2):** This value is not present in the data set and lacks mathematical relevance to the calculation. * **B (1.9):** This is the **Mode** (the most frequently occurring value), not the median. * **D (2.5):** This is the 6th and 7th term; selecting this ignores the rule for calculating the average of the two central points in an even-numbered data set. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Best Measure of Central Tendency:** For **skewed data** (e.g., incubation periods, income), the **Median** is the most appropriate measure. * **Nominal Data:** Use **Mode**. * **Ordinal Data:** Use **Median**. * **Interval/Ratio Data (Normal Distribution):** Use **Mean**. * **Relationship in Positive Skew:** Mean > Median > Mode. * **Relationship in Negative Skew:** Mode > Median > Mean. * **Note:** The Median corresponds to the **50th Percentile** and the **2nd Quartile ($Q_2$)**.

Q: A screening test was positive in 50% of the diseased population and 10% of the healthy population. What is the specificity of the test?

0.9. ### **Explanation** To solve this question, we must apply the definitions of diagnostic test parameters to the percentages provided. 1. **Understanding the Data:** * **Sensitivity:** The probability that the test is positive in a diseased person. The question states the test is positive in **50%** of the diseased population. Thus, Sensitivity = 0.50. * **False Positive Rate (α):** The probability that the test is positive in a healthy person. The question states the test is positive in **10%** of the healthy population. Thus, False Positive Rate = 0.10. 2. **Calculating Specificity:** Specificity is the ability of a test to correctly identify those without the disease (True Negative Rate). It is mathematically related to the False Positive Rate: * **Specificity = 1 – False Positive Rate** * Specificity = 1 – 0.10 = **0.9 (or 90%)** --- ### **Analysis of Options:** * **Option B (0.9) is Correct:** As calculated above, specificity is the complement of the positive rate in healthy individuals (100% - 10% = 90%). * **Option A (0.5) is Incorrect:** This represents the **Sensitivity** of the test (positive results in the diseased population). * **Option C (0.83) is Incorrect:** This value does not correlate with the provided data; it is often a distractor representing a calculated Positive Predictive Value in specific prevalence scenarios. * **Option D (0.064) is Incorrect:** This is a mathematical distractor with no relevance to the basic definitions of sensitivity or specificity. --- ### **High-Yield Clinical Pearls for NEET-PG:** * **SNOUT:** **S**ensitivity helps rule **OUT** a disease (used in screening). * **SPIN:** **S**pecificity helps rule **IN** a disease (used in confirmation). * **False Positive Rate** is also known as **Type I Error (α)**. * **False Negative Rate** is also known as **Type II Error (β)**; Sensitivity is calculated as **(1 – β)**.

Q: If the prevalence of Candida glabrata infection is found to be 80% in a population of 100, what will be the range of prevalence at a 95% confidence level?

72% to 88%. ### Explanation **1. Understanding the Correct Answer (C):** The question asks for the **95% Confidence Interval (CI)** for a proportion. In biostatistics, the formula for the 95% Confidence Interval is: **$CI = p \pm 1.96 \times SE$** *(Where $p$ = prevalence/proportion and $SE$ = Standard Error)* * **Step 1:** Identify the variables. $p = 80\%$ (0.8), $q = 20\%$ (0.2), and $n = 100$. * **Step 2:** Calculate Standard Error (SE) for proportion: $SE = \sqrt{\frac{p \times q}{n}} = \sqrt{\frac{80 \times 20}{100}} = \sqrt{\frac{1600}{100}} = \sqrt{16} = 4$. * **Step 3:** Apply the 95% CI formula (using 2 as a rounded value for 1.96 for quick calculation): $80 \pm (2 \times 4) = 80 \pm 8$. * **Lower Limit:** $80 - 8 = 72\%$ * **Upper Limit:** $80 + 8 = 88\%$ Thus, we are 95% confident that the true population prevalence lies between **72% and 88%**. **2. Why Other Options are Incorrect:** * **Option A & D:** These ranges are too wide. They suggest a much larger Standard Error, which would only occur with a significantly smaller sample size (e.g., $n < 10$). * **Option B:** This range (65% to 95%) implies a Standard Error of 7.5, which does not mathematically align with the given sample size of 100. **3. High-Yield Clinical Pearls for NEET-PG:** * **Standard Error (SE):** Measures the precision of the sample estimate. As sample size ($n$) increases, SE decreases, and the Confidence Interval becomes narrower (more precise). * **Confidence Levels:** * 95% CI = $Mean \pm 1.96 \times SE$ (Commonly used in research) * 99% CI = $Mean \pm 2.58 \times SE$ * 68% CI = $Mean \pm 1 \times SE$ * **Prevalence vs. Incidence:** Prevalence (Total cases/Total population) is a cross-sectional measure, whereas Incidence (New cases/Population at risk) is a longitudinal measure.

Question 1

In a study evaluating the health hazards of a drug versus a placebo, the following results were obtained: Placebo group: 15225 people, 1605 affected. Drug group: 15225 people, 1804 affected. Which of the following is true regarding the risk reduction?

Accepted Answer

RRR 11%, ARR 1%

Answer

Relative risk reduction (RRR) is 11%, Absolute risk reduction (ARR) is 11%

Answer

RRR 1%, ARR 11%

Answer

RRR 1%, ARR 1%

Question 2

A total of 5000 patients with glaucoma are identified and surveyed regarding family history of glaucoma. What is this study design called?

Accepted Answer

Case series report

Answer

Case-control study

Answer

Clinical trial

Answer

Cohort study

Question 3

Confounding factors can be eliminated by all except:

Accepted Answer

Ethical consideration

Answer

Matching

Answer

Randomization

Answer

Stratification

Question 4

The prevalence of diabetes mellitus in a population was found to be 10 percent. What is the probability that three people selected at random from the population have the disease?

Accepted Answer

0.001

Answer

0.003

Answer

0.03

Answer

0.01

Question 5

Calculate the median from the following values: 1.9, 1.9, 1.9, 2.1, 2.4, 2.5, 2.5, 2.9?

Accepted Answer

2.25

Answer

1.2

Answer

1.9

Answer

2.5

Question 6

Randomization is done in clinical trials to:

Accepted Answer

Avoid selection bias within the study group

Answer

Avoid bias from the general population

Answer

Eliminate comparability

Answer

Ensure comparability

Question 7

A screening test was positive in 50% of the diseased population and 10% of the healthy population. What is the specificity of the test?

Accepted Answer

0.9

Answer

0.5

Answer

0.83

Answer

0.064

Question 8

Which of the following best represents a population with age variation?

Accepted Answer

Population pyramid

Answer

Life table

Answer

Correlation coefficient

Answer

Barchart

Question 9

If the prevalence of Candida glabrata infection is found to be 80% in a population of 100, what will be the range of prevalence at a 95% confidence level?

Accepted Answer

72% to 88%

Answer

4% to 100%

Answer

65% to 95%

Answer

70% to 100%

Question 10

A person is studying the relationship between deafness and mobile phone usage. Data on mobile phone usage was collected from a government source, and data on deafness was collected from district and private clinics. What type of study is this?

Accepted Answer

Ecological study

Answer

Experimental study

Answer

Etiological study

Answer

Cross-sectional study

Biostatistics — MCQs

Biostatistics — MCQs

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