Biostatistics Practice Questions

Q: A new diagnostic test is introduced. Based on the image provided showing performance curves of both tests, what characteristics does the new test demonstrate compared to the old one?

Higher sensitivity and higher specificity. ***Correct Option: Higher sensitivity and higher specificity*** The blue curves (representing the new test) show **better separation between 'healthy' and 'diseased' populations** compared to the red curves (old test). This indicates improved discriminatory power. - The **reduced overlap** between the blue curves means fewer cases fall into the ambiguous zone - **Smaller FN (False Negative) region** → Higher sensitivity (better detection of diseased individuals) - **Smaller FP (False Positive) region** → Higher specificity (better identification of healthy individuals) - The **higher peak and clearer separation** demonstrate that the new test performs better in both correctly identifying disease when present AND correctly ruling out disease when absent *Incorrect: Higher sensitivity and lower specificity* - This would occur if the cutoff point was shifted to reduce false negatives at the cost of increasing false positives - The image shows BOTH FN and FP regions are smaller, not a trade-off *Incorrect: Lower sensitivity and higher specificity* - This would occur if the cutoff point was shifted to reduce false positives at the cost of increasing false negatives - Again, the image shows improvement in both parameters simultaneously *Incorrect: Lower sensitivity and lower specificity* - This represents a worse test with more overlap and larger FN/FP regions - The blue curves clearly show IMPROVEMENT, not deterioration, compared to the red curves

Q: Which type of statistical graph is shown in the image below?

Frequency polygon. ***Frequency polygon*** - A frequency polygon is constructed by plotting a **point at the midpoint of each class interval** at a height corresponding to its frequency, and then **connecting these points with straight lines**. - The image clearly shows points plotted and connected by straight lines, representing the frequency distribution, which is characteristic of a frequency polygon. *Histogram* - A histogram uses **contiguous bars to represent the frequency distribution** of continuous data, where the width of the bar represents the class interval and the height represents the frequency. - The image does not display bars, but rather a line graph connecting points, which differentiates it from a histogram. *Sector diagram* - A sector diagram, also known as a **pie chart**, divides a circle into sectors that represent proportions of a whole. - The image is a two-dimensional graph with x and y axes, not a circular representation of proportions. *Scatter diagram* - A scatter diagram displays **individual data points** for two variables to show their relationship, without connecting them with lines in a continuous manner like a frequency polygon. - While it shows points, they are connected to form a shape, indicating a distribution over intervals rather than individual data points of two distinct variables.

Q: The following scatter plot of 4 different samples shows the correlation between weight and height in the samples. All 4 samples have the same coefficient of correlation of 0.6 taken together, what will be the net correlation coefficient?

More than 0.6. ***More than 0.6*** - When multiple distinct samples (each with r = 0.6) are combined, the **overall correlation coefficient typically increases** beyond the individual correlations - This occurs because the **between-group variance** adds to the total variance when groups form separate clusters along the regression line - The combined dataset captures both the within-group correlation (0.6) and the systematic separation of groups, resulting in a stronger overall linear relationship - This is a well-recognized phenomenon in biostatistics: **pooled correlation > individual correlations when groups are spatially separated** *Less than 0.6* - This would occur only if the groups showed contradictory trends or if combining them obscured the linear relationship - Not applicable here since all groups show the same positive correlation and align along a common trend *Equal to 0.6* - This is incorrect because **the correlation coefficient of pooled data ≠ mean of individual correlations** - The pooled correlation is calculated from all combined data points, which includes both within-group and between-group variance - Mathematical property: when distinct clusters exist, pooling increases the correlation coefficient *Cannot be calculated* - The correlation coefficient **can be calculated** by pooling all data points and applying the standard Pearson correlation formula - Sufficient information exists to compute the combined correlation from the aggregated dataset

Q: What does the given image show?

Scatter diagram. ***Scatter diagram*** - A scatter diagram displays individual data points using **Cartesian coordinates**, where each point represents the values of two different variables, which are 'Weight' and 'Height' in this image. - It is used to observe the **relationship or correlation** between two quantitative variables. *Histogram* - A **histogram** is used to represent the **distribution of a single numerical variable**, divided into bins, and shows the frequency of data points falling into each bin. - This image clearly plots individual points for two variables, not frequency distributions within bins.

Q: What does the following diagram show?

***A line graph displaying average daily temperatures*** - The image presents a **line graph** with "Average daily temperatures" as its title. - The Y-axis is labeled "Temperature (°F)," indicating that the graph tracks temperature over a period, likely days.

Q: You are posted in the Army Medical Corps. The company officer is briefing you over the depth of snow in Rohtang pass over the period of last one month. This diagram is called as:

Histogram. ***Correct: Histogram*** - A **histogram** is used to represent the frequency distribution of a **continuous variable** over different time intervals or class intervals - In this case, the **depth of snow** (continuous quantitative data) is measured over **one month period** at Rohtang pass - Histograms display data using adjacent rectangular bars where the **height represents frequency or magnitude** and the **width represents class intervals** (time periods) - This is the standard method for showing trends of continuous environmental data over time in epidemiology and biostatistics *Incorrect: Scatter diagram* - Scatter diagrams are used to show the **relationship between two continuous variables** (bivariate data) - They display individual data points on X-Y coordinates to assess correlation - Not appropriate here as we're tracking a single variable (snow depth) over time, not examining relationships between two variables *Incorrect: Pie chart* - Pie charts represent **proportions or percentages** of categorical data as sectors of a circle - Used when showing parts of a whole (e.g., distribution of diseases, budget allocation) - **Cannot be used for continuous time-series data** like snow depth measurements - Not suitable for showing trends over time *Incorrect: Pictogram* - Pictograms use **pictures or symbols** to represent data quantities - Primarily used for simple visual representation for lay audiences - Less precise and not standard for scientific/medical data presentation - Not the conventional method for recording meteorological or environmental continuous data

Q: The person on the upper part of the image is an IV drug abuser who is undergoing rehabilitation. The people shown are either sexual contacts or person with whom he had shared a needle. From those contacts further information leads to multiple such drug addicts in the community who had not sought medical services till now. This is an example of:

Snowball sampling. ***Snowball sampling*** - This method involves **identifying initial subjects** (e.g., the IV drug abuser in rehabilitation) and then asking them to identify others within their network who fit the study criteria. - It is particularly useful for reaching **hidden or hard-to-reach populations**, such as IV drug abusers or individuals involved in stigmatized behaviors, as seen in this scenario where subsequent contacts lead to more unreached individuals. *Cluster sampling* - This method involves dividing the population into **clusters** (e.g., geographic areas) and then randomly sampling entire clusters. - It is not applicable here as the sampling is based on personal connections, not pre-defined groups or locations. *Stratified cluster sampling* - This is a combination of stratified and cluster sampling, where the population is first divided into **strata**, and then clusters are randomly sampled from each stratum. - This method is more complex and typically used when there's a need to ensure representation from specific subgroups within clusters, which is not the primary technique described. *Convenience sampling* - This method involves selecting participants who are **readily available** or easiest to access. - While the initial contact might seem convenient, the extended chain of referrals to find more individuals goes beyond mere convenience and represents a deliberate effort to leverage existing social networks.

Q: This is a map of an urban slum in New Delhi. The medical officer of PHC notified the higher authorities on observing multiple cases of measles in 1-2 years age group. The authorities conducted a survey of vaccine coverage in the area in the manner shown below. Which sampling is depicted here?

Cluster sampling. ***Cluster sampling*** - The image shows **groups (clusters)** of houses (red houses within red circles) being selected, and then all units within those selected groups are included in the sample. - This method is typically used when the population is naturally divided into groups, such as geographical areas or blocks, making it **cost-effective** and practical, especially in large, dispersed populations like an urban slum. *Simple random sampling* - This method would involve **randomly selecting individual houses** from the entire slum without any pre-defined grouping, which is not depicted in the image. - Each house would have an **equal chance of being selected**, and sampling would not be restricted to specific clusters. *Systematic random sampling* - Involves selecting houses at a **fixed interval** (e.g., every 5th house) from a sorted list or along a defined path after a random starting point. - The image does not show a systematic selection process or an underlying order for sampling the houses. *Stratified random sampling* - This method involves **dividing the population into homogeneous subgroups** (strata) based on a characteristic (e.g., age, income level) and then drawing a random sample from each stratum. - While the map shows 'sections', these are not necessarily strata based on a relevant characteristic, and the sampling is not shown to be proportional or disproportional across these sections.

Q: A professor at AIIMS was asked to conduct a study on hazardous effects of cellphone use on health of urban Indians. He selected the study group in the fashion shown below. It indicates:

Cluster random sampling. **Cluster random sampling** - The image shows distinct **groups (clusters)** like "Reliance," "Airtel," and "Vodafone," from which entire clusters or randomly selected individuals from within certain clusters are chosen for the sample. - In this method, the **population is divided into clusters**, and then a random sample of these clusters is drawn. All units within the selected clusters (or a random selection of units within selected clusters) are included in the sample. - This is the sampling method depicted in the image. *Simple random sampling* - This method involves selecting subjects from the entire population **randomly and independently**, where each member has an equal chance of being selected. - The image illustrates pre-defined groups and selection from within and between them, which isn't characteristic of a single, undifferentiated pool for simple random selection. *Systematic random sampling* - This technique involves selecting every **k-th individual** from a list, after a random start. - The visual representation does not suggest a continuous list or a patterned, interval-based selection process. *Stratified random sampling* - In this method, the population is divided into **homogeneous subgroups (strata)** based on shared characteristics, and then a simple random sample is drawn from each stratum. - While there are groups (Reliance, Airtel, Vodafone), the selection process shown (selecting some individuals from one group, some from another, and possibly an entire smaller group from a larger one) does not strictly adhere to sampling proportionally from each stratum to ensure representation.

Q: The given image shows which kind of sampling?

Systematic random sampling. ***Systematic random sampling*** - The image illustrates **systematic random sampling** where participants are selected at regular intervals from a list, using a starting point chosen randomly. - For example, if we have 100 people and want to sample 10, we could pick every 10th person after a random start between 1 and 10. *Simple random sampling* - In **simple random sampling**, every individual in the population has an **equal chance** of being selected, like drawing names from a hat. - The image does not show a random selection of individuals from the entire pool without any specific pattern or interval. *Stratified random sampling* - **Stratified random sampling** involves dividing the population into **subgroups (strata)** based on shared characteristics, then taking a random sample from each stratum. - The image does not show any deliberate division of the population into distinct strata before sampling. *Cluster random sampling* - **Cluster random sampling** involves dividing the population into **clusters**, randomly selecting entire clusters, and then sampling all individuals within the chosen clusters. - The image does not depict the selection of entire pre-defined groups or clusters of individuals.

Question 1

A new diagnostic test is introduced. Based on the image provided showing performance curves of both tests, what characteristics does the new test demonstrate compared to the old one?

Accepted Answer

Higher sensitivity and higher specificity

Answer

Higher sensitivity and lower specificity

Answer

Lower sensitivity and higher specificity

Answer

Lower sensitivity and lower specificity

Question 2

Which type of statistical graph is shown in the image below?

Accepted Answer

Frequency polygon

Answer

Histogram

Answer

Sector diagram

Answer

Scatter diagram

Question 3

The following scatter plot of 4 different samples shows the correlation between weight and height in the samples. All 4 samples have the same coefficient of correlation of 0.6 taken together, what will be the net correlation coefficient?

Accepted Answer

More than 0.6

Answer

Less than 0.6

Answer

Equal to 0.6

Answer

Cannot be calculated

Question 4

What does the given image show?

Accepted Answer

Scatter diagram

Answer

Histogram

Answer

Bar chart

Answer

Pie chart

Question 5

What does the following diagram show?

Question 6

You are posted in the Army Medical Corps. The company officer is briefing you over the depth of snow in Rohtang pass over the period of last one month. This diagram is called as:

Accepted Answer

Histogram

Answer

Scatter diagram

Answer

Pie chart

Answer

Pictogram

Question 7

The person on the upper part of the image is an IV drug abuser who is undergoing rehabilitation. The people shown are either sexual contacts or person with whom he had shared a needle. From those contacts further information leads to multiple such drug addicts in the community who had not sought medical services till now. This is an example of:

Accepted Answer

Snowball sampling

Answer

Cluster sampling

Answer

Stratified cluster sampling

Answer

Convenience sampling

Question 8

This is a map of an urban slum in New Delhi. The medical officer of PHC notified the higher authorities on observing multiple cases of measles in 1-2 years age group. The authorities conducted a survey of vaccine coverage in the area in the manner shown below. Which sampling is depicted here?

Accepted Answer

Cluster sampling

Answer

Simple random sampling

Answer

Systematic random sampling

Answer

Stratified random sampling

Question 9

A professor at AIIMS was asked to conduct a study on hazardous effects of cellphone use on health of urban Indians. He selected the study group in the fashion shown below. It indicates:

Accepted Answer

Cluster random sampling

Answer

Simple random sampling

Answer

Systematic random sampling

Answer

Stratified random sampling

Question 10

The given image shows which kind of sampling?

Accepted Answer

Systematic random sampling

Answer

Simple random sampling

Answer

Stratified random sampling

Answer

Cluster random sampling

Biostatistics — MCQs

Biostatistics — MCQs

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