Biostatistics Practice Questions

Q: Two laboratories have developed testing for Zika virus. The statistical method shown below was used to compare the diagnostic performance of these tests. What is this statistical method called?

ROC curve. ***ROC curve*** - This graph, displaying **true positive rate (sensitivity)** against the **false positive rate (1-specificity)**, is characteristic of a **Receiver Operating Characteristic (ROC) curve**. - ROC curves are commonly used to evaluate and compare the performance of **diagnostic tests** or predictive models across various threshold settings. *Lorenz curve* - A Lorenz curve is used in economics to represent **income inequality** or wealth distribution. - It plots the proportion of total income/wealth owned by the bottom x% of the population, and does not relate to diagnostic test performance. *Bell curve* - A bell curve, or **normal distribution curve**, is a symmetrical graph that shows the distribution of a **continuous variable**. - It describes how data points are distributed around the mean, not the performance of diagnostic tests. *Gaussian curve* - A Gaussian curve is another name for a **normal distribution** or **bell curve**. - It is used to model random variables in statistics, not to compare the sensitivity and specificity of diagnostic tests in the manner shown.

Q: A study was conducted to find out the number of positive lymph nodes in a population of breast cancer patients who underwent axillary dissection. A graph as shown below was plotted between the number and frequency of positive nodes. Which of the following is correct?

A: Mode, B: Median, C: Mean. ***A: Mode, B: Median, C: Mean*** - In a **positively skewed distribution**, the **mode** is the value that appears most frequently (highest peak), which is A. - The **median** is the middle value when data are ordered, and in a positively skewed distribution, it falls between the mode and the mean (point B). - The **mean** is the average of all values, and it is pulled towards the tail of the skew, making it the highest value among the three in a positively skewed distribution (point C). *A: Mean, B: Median, C: Mode* - This order would be correct for a **negatively skewed distribution**, where the tail extends to the left, and the mean is the smallest. - However, the given graph clearly shows a **positive skew**, with the peak at the beginning and the tail extending to the right. *A: Median, B: Mean, C: Mode* - This arrangement does not correspond to a standard distribution pattern, whether skewed positively or negatively. - The median, mean, and mode have established relative positions depending on the **skewness** of the data. *A: Mean, B: Mode, C: Median* - This option incorrectly places the **mode** in the middle and the **mean** at the beginning of the distribution. - This order is inconsistent with the characteristics of any common type of data distribution.

Q: In comparison of pulse oximeter reading in neonates with and without micropore, which of the following is true about the plot shown below?

Bland Altman plot. ***Bland Altman plot*** - This plot is used to **assess agreement between two different methods of measurement** by plotting the difference between the two measurements against their average. - The plot displays the **mean difference** (red line) and **limits of agreement** (+/- 1.96 standard deviation, blue lines), indicating how well the two SpO2 measurements agree. *Funnel plot* - A funnel plot is primarily used in **meta-analyses** to check for publication bias or small study effects. - It plots the **effect size** from individual studies against a measure of their precision (e.g., standard error). *Forest plot* - A forest plot is used in **meta-analyses** to graphically present the results of individual studies included in the review, along with the overall summary effect. - It typically shows the **effect estimate and confidence interval** for each study, and a diamond representing the pooled estimate. *Kaplan Meier plot* - This plot is used to estimate the **survival function** from lifetime data, showing the probability of an event (e.g., death, disease recurrence) occurring over time. - It is commonly used in **clinical trials** to compare survival rates between different treatment groups.

Q: A new test in red line has been designed to diagnose a disease condition. The test is applied to both normal and diseased population, the graph of which is given below. Which of the following is correct regarding the test?

Low sensitivity and low specificity. ***Low sensitivity and low specificity*** - In the provided graph, the **red line** curve (new test) for the healthy and diseased populations shows substantial **overlap**, meaning there is poor discrimination between the two groups. - A test with **low sensitivity** will miss many true positive cases (diseased individuals), and a test with **low specificity** will incorrectly identify many healthy individuals as diseased, both of which are indicated by the extensive overlap. *High sensitivity and high specificity* - This would be represented by two curves that are **well-separated**, with minimal overlap, allowing for clear distinction between healthy and diseased individuals. - Such a test would correctly identify most diseased individuals (**high sensitivity**) and most healthy individuals (**high specificity**). *High sensitivity and low specificity* - This would typically show a test that correctly identifies most diseased individuals (high true positive rate), but also incorrectly flags many healthy individuals as diseased (high false positive rate). - Graphically, this might appear as the diseased curve being mostly captured, but with significant spillover into the healthy range. *Low sensitivity and high specificity* - This scenario suggests a test that rarely misidentifies healthy individuals as diseased (low false positive rate), but also misses many diseased individuals (high false negative rate). - The healthy curve would be well-defined and distinct, but the diseased curve would significantly overlap with the healthy curve, indicating poor detection of disease.

Q: Sample size of samples A, B and C are 500, 800 and 1000 respectively. Which sample has the highest margin of error? (NEET Jan 2018)

Sample A. ***Sample A*** - The **margin of error** is inversely proportional to the square root of the sample size. Therefore, a smaller sample size leads to a larger margin of error. - Sample A has the smallest sample size (N=500) among the given options, thus having the **highest margin of error**. *Sample B* - With a sample size of 800, Sample B has a **smaller margin of error** than Sample A but a larger margin of error than Sample C. - As the sample size increases, the precision of the estimate improves, and the margin of error decreases. *Sample C* - Sample C has the largest sample size (N=1000), which results in the **smallest margin of error** among all samples. - A larger sample size generally provides a more accurate representation of the population. *None of above* - This option is incorrect because the sample size directly influences the margin of error, and Sample A clearly has the smallest size. - Based on statistical principles, one of the samples must inherently have the highest margin of error.

Q: Which of the following is true about the box plot shown?

Mean = median, not equal to mode. ***Mean = median, not equal to mode*** - A **perfectly symmetrical distribution** (represented by a **symmetrical box plot without whiskers extending further in one direction**) indicates that the **mean and median are equal**. - However, the mode, which is the most frequent value, is not necessarily equal to the mean and median in all symmetrical distributions, especially if it's **not unimodal or not centered at the mean/median**. When depicted using a boxplot, we cannot ascertain the mode simply by looking at where the median lies. *Mean = median = mode* - While the **mean and median are equal** in a symmetrical distribution, the **mode is not explicitly represented** in a box plot. - The mode is the most frequently occurring value, and a box plot primarily shows quartiles and spread, not individual frequencies. *Mean = mode, not equal to median* - In a symmetrical distribution, the **mean and median are equal**. - Therefore, this option is incorrect as it states the mean is not equal to the median. *Mean, median and mode are not equal* - The **symmetrical nature** of the box plot strongly suggests that the **mean and median are equal**. - This option is therefore incorrect, as at least two of the measures of central tendency are equal.

Q: Which is incorrect about the image shown below?

75 % values are above 25 mg. ***75 % values are above 25 mg*** - This statement is incorrect. In a box plot, the **second quartile (Q2)** or **median** represents the 50th percentile. The upper boundary of the lower box (Q2) is at 23 mg, meaning 50% of values are above 23 mg. - The upper boundary of the upper box (Q3) is at 35 mg, meaning 25% of values are above 35 mg. Therefore, it is incorrect to say 75% of values are above 25 mg. *Negatively skewed* - The long **tail of the distribution** is on the left side, as indicated by the lower whisker extending further from the box than the upper whisker, and the lower half of the box being larger than the upper half. - In a negatively skewed distribution, the **mean is typically less than the median**, and the bulk of the values are concentrated on the higher end. *Positively skewed* - This statement is incorrect. A **positively skewed** distribution would have a longer tail on the right side, meaning the upper whisker would be longer than the lower whisker and the upper box larger than the lower box. - The provided image shows the opposite, with the longer tail towards the lower values. *Median is 50 mg* - The **median** is represented by the line dividing the lower and upper halves of the box. In this box plot, the median line is at approximately **23 mg**, not 50 mg. - The box itself represents the **interquartile range (IQR)**, with the median dividing it.

Q: A study was conducted to evaluate the diagnostic accuracy of ECG for detecting myocardial infarction. The results are shown in the 2x2 table below: Myocardial Infarction Present Absent Total ECG Positive 45 8,000 8,045 ECG Negative 5 32,000 32,005 Total 50 40,000 40,050 Consider the following statements: I. Sensitivity is 90%. II. Specificity is 80%. Which of the statements given above is/are correct?

Both I and II. **Both I and II** - **Sensitivity** = True Positives / (True Positives + False Negatives) = 45 / (45 + 5) = 45/50 = **0.90 or 90%** ✓ - **Specificity** = True Negatives / (True Negatives + False Positives) = 32,000 / (32,000 + 8,000) = 32,000/40,000 = **0.80 or 80%** ✓ - Both calculations are correct based on the 2×2 contingency table - **Sensitivity** measures the ability of the test to correctly identify those with disease (true positive rate) - **Specificity** measures the ability of the test to correctly identify those without disease (true negative rate) *I only* - Incorrect because Statement II (Specificity = 80%) is also correct, not just Statement I *II only* - Incorrect because Statement I (Sensitivity = 90%) is also correct, not just Statement II *Neither I nor II* - Incorrect because both statements are mathematically correct based on the given data

Q: A surgical department of a premier medical college conducted a study on rates of post-operative wound infection. The results of the study were negative for the proposed hypothesis. What should the department do with the results?

Report the negative results. **Report the negative results** - All research findings, whether positive or negative, contribute to the body of scientific knowledge and should be **ethically reported** to prevent publication bias. - Reporting negative results helps other researchers avoid duplicating efforts and can inform future study designs, potentially leading to a better understanding of the topic. *Label them as worthless* - Labeling negative results as "worthless" contradicts the principles of **scientific integrity** and promotes publication bias, where only positive findings are disseminated. - Even negative findings can provide crucial insights, indicating that a particular intervention or hypothesis is not supported, thus saving time and resources for future research. *Redo the study with a new hypothesis* - While forming new hypotheses may be necessary in some cases, redoing the study with a completely new hypothesis without reporting the initial negative results would be **unethical** and contribute to the problem of **publication bias**. - **New hypotheses** should ideally be formulated based on a comprehensive understanding of existing research, including negative findings. *Redesign the study and increase the sample size* - While redesigning the study and increasing sample size might be appropriate after the initial results have been reported and analyzed, the **immediate and ethical step** is to report the existing negative findings. - A larger sample size alone does not guarantee positive results; careful reevaluation of the methods and hypothesis is needed if the initial study was well-conducted.

Q: Cross-over type of study designs are those in which each subject serves as his/her own control. In which of the following conditions is a cross-over study not suitable ?

If the drug of interest cures the disease. ***If the drug of interest cures the disease*** - A **crossover study** relies on subjects experiencing both treatment and control conditions, which is **not possible** if a drug cures the disease, as the initial treatment would eliminate the condition for the second phase. - The carryover effect of a cure would invalidate the comparison between the treatment and control periods, making subsequent observations on the same subject non-independent. *If the disease changes radically during the period of time required for the study* - **Radical changes in disease progression** would introduce significant **confounding variables**, making it difficult to attribute changes in outcome solely to the intervention. - The **baseline state** for the second treatment period would be vastly different from the first, violating the assumption of comparable conditions inherent in crossover designs. *None of the options* - This option is incorrect because there is a specific scenario among the choices where a crossover study is unsuitable, as detailed in the correct answer. *If the drug is effective during all stages of the disease* - A drug's effectiveness across all disease stages would actually **make a crossover study more suitable**, as the treatment effects could be consistently observed regardless of when the intervention is given. - This scenario would reduce the variability in response due to disease progression, allowing for a clearer comparison between treatment and control periods.

Question 1

Two laboratories have developed testing for Zika virus. The statistical method shown below was used to compare the diagnostic performance of these tests. What is this statistical method called?

Accepted Answer

ROC curve

Answer

Lorenz curve

Answer

Bell curve

Answer

Gaussian curve

Question 2

A study was conducted to find out the number of positive lymph nodes in a population of breast cancer patients who underwent axillary dissection. A graph as shown below was plotted between the number and frequency of positive nodes. Which of the following is correct?

Accepted Answer

A: Mode, B: Median, C: Mean

Answer

A: Mean, B: Median, C: Mode

Answer

A: Median, B: Mean, C: Mode

Answer

A: Mean, B: Mode, C: Median

Question 3

In comparison of pulse oximeter reading in neonates with and without micropore, which of the following is true about the plot shown below?

Accepted Answer

Bland Altman plot

Answer

Funnel plot

Answer

Forest plot

Answer

Kaplan Meier plot

Question 4

A new test in red line has been designed to diagnose a disease condition. The test is applied to both normal and diseased population, the graph of which is given below. Which of the following is correct regarding the test?

Accepted Answer

Low sensitivity and low specificity

Answer

High sensitivity and high specificity

Answer

High sensitivity and low specificity

Answer

Low sensitivity and high specificity

Question 5

Sample size of samples A, B and C are 500, 800 and 1000 respectively. Which sample has the highest margin of error? (NEET Jan 2018)

Accepted Answer

Sample A

Answer

Sample B

Answer

Sample C

Answer

None of above

Question 6

Which of the following is true about the box plot shown?

Accepted Answer

Mean = median, not equal to mode

Answer

Mean = median = mode

Answer

Mean = mode, not equal to median

Answer

Mean, median and mode are not equal

Question 7

Which is incorrect about the image shown below?

Accepted Answer

75 % values are above 25 mg

Answer

Negatively skewed

Answer

Positively skewed

Answer

Median is 50 mg

Question 8

A study was conducted to evaluate the diagnostic accuracy of ECG for detecting myocardial infarction. The results are shown in the 2x2 table below:

Myocardial Infarction
                    Present    Absent    Total
ECG Positive         45       8,000     8,045
ECG Negative          5      32,000    32,005
Total                50      40,000    40,050

Consider the following statements:
I. Sensitivity is 90%.
II. Specificity is 80%.

Which of the statements given above is/are correct?

Accepted Answer

Both I and II

Answer

Neither I nor II

Answer

II only

Answer

I only

Question 9

A surgical department of a premier medical college conducted a study on rates of post-operative wound infection. The results of the study were negative for the proposed hypothesis. What should the department do with the results?

Accepted Answer

Report the negative results

Answer

Label them as worthless

Answer

Redo the study with a new hypothesis

Answer

Redesign the study and increase the sample size

Question 10

Cross-over type of study designs are those in which each subject serves as his/her own control. In which of the following conditions is a cross-over study not suitable ?

Accepted Answer

If the drug of interest cures the disease

Answer

If the disease changes radically during the period of time required for the study

Answer

None of the options

Answer

If the drug is effective during all stages of the disease

Biostatistics — MCQs

Biostatistics — MCQs

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