Biostatistics Practice Questions

Q: Which of the following is not a method of random sampling?

Quota sampling. ***Quota sampling*** - **Quota sampling** is a non-probability sampling method where researchers select a sample based on pre-defined characteristics to match the population's proportions. - It does not involve random selection at any stage, making it a non-random sampling technique. *Cluster sampling* - **Cluster sampling** is a probability (random) sampling technique where the population is divided into clusters, and then a random sample of these clusters is selected. - All units within the selected clusters are then included in the sample, or a random sample is taken from within the selected clusters. *Stratified sampling* - **Stratified sampling** is a probability (random) sampling method that involves dividing the population into homogeneous subgroups (strata) and then taking a random sample from each stratum. - This method ensures representation from all important subgroups within the population. *Simple random* - **Simple random sampling** is a basic probability (random) sampling technique where every member of the population has an equal chance of being selected for the sample. - This method is considered the most fundamental type of random sampling.

Q: Which of the following is a true statement regarding longitudinal studies?

Incidence rate can be calculated. ***Correct: Incidence rate can be calculated*** - **Longitudinal studies** follow participants over time, allowing researchers to identify **new cases** of disease as they occur - Since the population at risk is followed prospectively, **incidence rates** (the rate at which new cases develop) can be accurately calculated - This is a **key advantage** that distinguishes longitudinal studies from cross-sectional studies, which can only calculate **prevalence** - Calculation of incidence is essential for understanding **disease risk** and evaluating **temporal relationships** between exposure and outcome *Studies natural history of disease* - While longitudinal studies CAN observe disease progression over time, this is not their most specific or defining characteristic - Many study designs (including case series and registry studies) can study natural history - **Natural history studies** are a specific subset of longitudinal studies, not a universal feature *Primarily designed to establish causation* - Longitudinal studies provide **evidence for temporal relationships** but are not primarily designed to establish causation - **Randomized controlled trials (RCTs)** are the gold standard for establishing causation through randomization and control of confounding variables - Longitudinal observational studies are subject to confounding and bias, limiting causal inference *More time consuming than cross-sectional studies* - While factually true, this describes a **limitation** rather than a defining characteristic or advantage - Many study designs are time-consuming; this is not specific to longitudinal studies - The question asks for a true statement that characterizes what longitudinal studies ARE or DO, not their practical constraints

Q: Which of the following statements about the normal distribution curve is true?

Mean = Median. ***Mean = Median*** - In a **normal distribution curve**, the data is perfectly symmetrical around its center. - This symmetry ensures that the **mean, median, and mode** all coincide at the peak of the curve. - This is a defining characteristic of the **Gaussian (normal) distribution**. *Mean = 2 Median* - This statement is incorrect; in a **normal distribution**, the mean and median are equal, not a multiple of each other. - Such a relationship (Mean = 2 Median) would imply a **positively skewed distribution**, which is not characteristic of a normal distribution. *Median = Variance* - The **median** is a measure of **central tendency**, representing the middle value of the data set. - **Variance** is a measure of **data dispersion** (how spread out the data is), measured in squared units. - These two measures are fundamentally different concepts and generally not equal. *Standard Deviation = 2 Variance* - **Standard deviation** is the **square root of the variance** (SD = √Variance), not twice the variance. - This relationship is mathematically incorrect and does not hold true for any distribution.

Q: What is the definition of literacy according to census standards?

Ability to read and write. ***Ability to read and write*** - According to most census standards, **literacy** is fundamentally defined as the ability of an individual to **read and write a simple message** in any language. - This definition focuses on the basic functional capacity to engage with written communication, rather than advanced proficiency. *Participation in a literacy program* - While participating in a literacy program indicates an effort towards improving literacy, it does not, by itself, define the current **literacy status** according to census standards. - An individual might attend such a program without yet acquiring the functional ability to **read and write**. *Ability to read and write fluently* - **Fluency** implies a high level of proficiency and speed in reading and writing, which goes beyond the basic definition of literacy used in census data collection. - Census standards typically only require the **basic capacity** to read and write. *Ability to write a simple sentence* - This option only covers the **writing aspect** of literacy and omits the crucial component of being able to **read**. - Census definitions require both reading and writing capabilities to be considered literate.

Q: Which of the following is obtained by joining the midpoints of histogram blocks in statistics?

Frequency polygon. ***Frequency polygon*** - A **frequency polygon** is constructed by plotting a point at the midpoint of the top of each histogram bar and then connecting these points with straight lines. - It is used to display the **frequency distribution** of continuous data, similar to a histogram, but can also compare multiple distributions on one graph. *Pictogram* - A **pictogram** uses images or symbols to represent data, where each symbol represents a certain quantity. - It simplifies data for broader audiences but is not derived directly from histogram blocks. *Bar chart* - A **bar chart** uses rectangular bars of varying heights or lengths to represent data for different categories. - Unlike a histogram, bar charts typically represent **categorical data** and have gaps between bars. *Pie chart* - A **pie chart** is a circular statistical graphic divided into slices to illustrate numerical proportion. - Each slice represents a category's proportion of the whole and is not related to histogram blocks or their midpoints.

Q: Specificity of a diagnostic test is defined as:

TN/(TN+FP). ***TN/(TN+FP)*** - **Specificity** is the proportion of individuals without disease who test negative, calculated as **TN/(TN+FP)**. - It indicates how well a test correctly identifies healthy individuals as negative. *TN/(TN+FN)* - This formula incorrectly pairs true negatives with false negatives, which does not represent specificity. - False negatives occur among diseased individuals, not among healthy individuals, so this formula is not a standard diagnostic test measure. *TP/(TP+FP)* - This formula represents **positive predictive value (PPV)**, not specificity. - PPV measures the proportion of positive test results that are truly positive. *TP/(TP+FN)* - This formula represents **sensitivity**, which is the proportion of diseased individuals who test positive. - **Sensitivity** focuses on correctly identifying diseased individuals, which is different from specificity that focuses on healthy individuals.

Q: In the context of medical statistics, which graphical representation is used to show the proportion of different categories of a variable in a dataset?

Pie. ***Option A: Pie*** - A **pie chart** is ideal for displaying **proportions** of different categories within a whole, where each slice represents a percentage of the total. - It clearly shows how each category contributes to the **overall dataset**, making it easy to visualize relative frequencies and the **part-to-whole relationship**. *Option B: Bar* - A **bar graph** is typically used to compare the **magnitudes** or frequencies of different categorical variables, rather than their proportion of a whole. - While it can show counts for categories, it doesn't directly represent the **part-to-whole relationship** as effectively as a pie chart. *Option C: Histogram* - A **histogram** is used to represent the **distribution of continuous numerical data**, grouping values into bins and displaying their frequencies. - It is not suitable for showing proportions of different **categorical variables**. *Option D: Pictogram* - A **pictogram** uses **pictures or symbols** to represent data, often in a simplified and engaging way. - While it can represent frequencies or counts, it is less precise for showing exact **proportions** of categories compared to a pie chart.

Q: Which of the following statements about screening tests is correct?

Sensitivity is 1 - False negative rate. ***Sensitivity is 1 - False negative rate*** - **Sensitivity** refers to the proportion of **true positive results** among all individuals with the disease. - The **false negative rate** is the proportion of individuals with the disease who test negative, so **1 - false negative rate** correctly defines sensitivity. *Sensitivity is 1 - False positive rate* - The false positive rate (1 - specificity) is related to the proportion of individuals without the disease who test positive. - This statement incorrectly defines sensitivity, confusing it with concepts related to specificity. *Post-test probability is only influenced by pre-test probability* - **Post-test probability** is influenced by both the **pre-test probability** and the **likelihood ratio** of the diagnostic test. - The **likelihood ratio** incorporates the test's sensitivity and specificity, making it a critical factor in modifying the probability of disease after testing. *None of the options is correct.* - The first statement, "Sensitivity is 1 - False negative rate," is a correct definition of sensitivity.

Q: Which of the following is not considered a type of subject bias?

Selection bias. ***Selection bias*** - **Selection bias** occurs when participants are chosen or remain in a study in a way that introduces a systematic error, leading to a sample that does not accurately represent the target population. - It is a **study design and sampling issue** that occurs at the **recruitment** or **retention stage**, not a bias arising from the subjects' own behavior or reporting. - Unlike subject biases, selection bias is introduced by the **investigators or study methodology**, not by the participants themselves. *Recall bias* - **Recall bias** is a type of **subject bias** where participants differentially remember and report past exposures based on their outcome status. - Subjects with disease may recall exposures more accurately than healthy controls, introducing **systematic error from the subject's memory**. *Hawthorne bias* - **Hawthorne bias** (observer effect) is a **subject bias** where participants modify their behavior because they know they are being studied. - The **subject's awareness** of observation directly influences their actions, responses, or adherence. *Reporting bias* - **Reporting bias** is a **subject bias** where participants selectively disclose or withhold information based on social desirability, embarrassment, or perceived consequences. - This bias arises from the **subject's decision** about what to report.

Question 1

Which of the following is not a method of random sampling?

Accepted Answer

Quota sampling

Answer

Cluster sampling

Answer

Stratified sampling

Answer

Simple random

Question 2

Which of the following is a true statement regarding longitudinal studies?

Accepted Answer

Incidence rate can be calculated

Answer

Studies natural history of disease

Answer

Primarily designed to establish causation

Answer

More time consuming than cross-sectional studies

Question 3

After applying a statistical test, an investigator gets a p-value of 0.01. What does this indicate about the null hypothesis?

Accepted Answer

There is a 1% probability of observing the data, or something more extreme, if the null hypothesis is true.

Answer

There is a 1% probability of incorrectly rejecting the null hypothesis when it is true.

Answer

The test has a 99% chance of detecting a true effect if it exists.

Answer

The null hypothesis is likely to be rejected.

Question 4

Which of the following statements about the normal distribution curve is true?

Accepted Answer

Mean = Median

Answer

Mean = 2 Median

Answer

Median = Variance

Answer

Standard Deviation = 2 Variance

Question 5

What is the definition of literacy according to census standards?

Accepted Answer

Ability to read and write

Answer

Participation in a literacy program

Answer

Ability to read and write fluently

Answer

Ability to write a simple sentence

Question 6

Which of the following is obtained by joining the midpoints of histogram blocks in statistics?

Accepted Answer

Frequency polygon

Answer

Pictogram

Answer

Bar chart

Answer

Pie chart

Question 7

Specificity of a diagnostic test is defined as:

Accepted Answer

TN/(TN+FP)

Answer

TP/(TP+FN)

Answer

TP/(TP+FP)

Answer

TN/(TN+FN)

Question 8

In the context of medical statistics, which graphical representation is used to show the proportion of different categories of a variable in a dataset?

Accepted Answer

Pie

Answer

Bar

Answer

Histogram

Answer

Pictogram

Question 9

Which of the following statements about screening tests is correct?

Accepted Answer

Sensitivity is 1 - False negative rate

Answer

Sensitivity is 1 - False positive rate

Answer

Post-test probability is only influenced by pre-test probability

Answer

None of the options is correct.

Question 10

Which of the following is not considered a type of subject bias?

Accepted Answer

Selection bias

Answer

Recall bias

Answer

Hawthorne bias

Answer

Reporting bias

Biostatistics — MCQs

Biostatistics — MCQs

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