Biostatistics Practice Questions

Q: Which of the following is NOT a characteristic of a health index?

Affordability. ***Affordability*** - **Affordability** is not considered a defining characteristic or psychometric property of a health index itself. - The core characteristics of a health index relate to its **measurement properties** (validity, reliability, sensitivity) and **practical applicability** (feasibility), not economic considerations. - While cost may influence whether a health index is adopted in practice, it does not determine the index's ability to accurately measure health status. - Affordability is an external factor related to resource availability rather than an intrinsic quality of the measurement tool. *Validity* - **Validity** is a fundamental characteristic referring to whether a health index measures what it intends to measure. - Types include content validity, criterion validity, and construct validity. - Essential for ensuring the index accurately reflects the health concept being assessed. *Reliability* - **Reliability** is a core characteristic indicating consistency and reproducibility of measurements. - Includes test-retest reliability, inter-rater reliability, and internal consistency. - A reliable health index produces stable results when measuring the same phenomenon under similar conditions. *Feasibility* - **Feasibility** is a recognized characteristic referring to the practical usability of a health index in real-world settings. - Includes ease of administration, time requirements, scoring simplicity, and acceptability to users. - A feasible index can be implemented effectively within available resources and constraints, though this differs from the economic concept of affordability.

Q: In a study a patient does not know the nature of drug [whether a placebo or curative drug] he is taking. The researcher knows the drug type to be given to the individuals in study. Type of blinding in this study is?

Single. ***Single*** - In **single-blinded studies**, the participant (patient) is unaware of whether they are receiving the experimental treatment or a placebo. - The investigator (researcher) and/or staff administering the treatment are aware of the treatment assignment. *Double* - In a **double-blinded study**, neither the participants nor the investigators/staff administering the treatment know who is receiving the experimental treatment and who is receiving the placebo. - This method helps to minimize bias from both participant expectations and researcher influence. *Triple* - A **triple-blinded study** extends double-blinding by also ensuring that those analyzing the data are unaware of the treatment assignments. - This adds an extra layer of protection against bias in the interpretation of results. *Combined double/triple* - This option refers to scenarios where a study design might aim to incorporate aspects of both double and triple blinding. - However, in this specific case, the researcher's knowledge of the drug type prevents it from being a fully double or triple-blinded study.

Q: Which of the following is a parametric test?

Student t-test. ***Student t-test*** - The **Student t-test** is a **parametric test** used to compare the means of two groups. - It assumes the data is **normally distributed** and has **equal variances**. *Sign test* - The **Sign test** is a **non-parametric test** used for paired data. - It examines the direction of differences between pairs, not their magnitude. *Fisher exact test* - The **Fisher exact test** is a **non-parametric test** used for analyzing **categorical data** in a 2x2 contingency table. - It is particularly useful when **sample sizes are small** and the assumptions for a chi-square test are not met. *Chi-square test* - The **Chi-square test** is a **non-parametric test** used to assess independence between **categorical variables** or to compare observed frequencies with expected frequencies. - It does not assume any specific distribution for the data, making it suitable for nominal data.

Q: In a positively skewed distribution, which of the following is true?

Mean > Median > Mode. ***Mean > Median > Mode*** - In a **positively skewed distribution**, the tail of the distribution is longer on the right side, meaning there are more extreme large values. - These large values pull the **mean** towards the right, making it greater than the **median**, which in turn is greater than the **mode**. *Mean = Median = Mode* - This equality holds true for a **symmetrical distribution**, such as a normal distribution, where data points are evenly distributed around the center. - A **positively skewed distribution** is asymmetrical, with a distinct longer tail on one side due to outliers. *Mode > Median > Mean* - This relationship is characteristic of a **negatively skewed distribution**, where the tail extends to the left, indicating a presence of more extreme small values. - In such a case, the **mode** is the largest and the **mean** is the smallest, pulled by the left-skewed tail. *None of the options* - This option is incorrect because the statement **Mean > Median > Mode** accurately describes the relationship between these measures of central tendency in a **positively skewed distribution**. - The other options describe different types of distributions.

Q: The figure below represents a statistical distribution. What type of skewness does it exhibit?

Right skewed. ***Right skewed*** - A distribution is **right-skewed** (positively skewed) when its tail extends longer to the right side, indicating that the majority of the data points are concentrated on the left side of the distribution. - In a right-skewed distribution, the **mean** is typically greater than the **median**, which is also greater than the **mode** (Mean > Median > Mode). *Normal distribution* - A **normal distribution** is **symmetrical**, meaning its left and right sides are mirror images, with no skewness. - In a normal distribution, the **mean, median, and mode** are approximately equal and located at the center of the distribution. *Left skewed* - A **left-skewed** (or negatively skewed) distribution has a tail that extends longer to the left side, with a concentration of data points on the right. - For a left-skewed distribution, the **mean** is usually less than the **median**, which is less than the **mode** (Mean < Median < Mode). *Bimodal distribution* - A **bimodal distribution** has two distinct peaks or modes, indicating two different groups or subpopulations in the data. - This is different from skewness, which describes the asymmetry of a single-peaked distribution.

Q: In a standard normal distribution curve, what percentage of the area under the curve lies between the mean and one standard deviation from the mean?

34%. ***34%*** - In a **standard normal distribution**, approximately 34.1% of the data falls between the **mean** and one **standard deviation** above the mean, and similarly, 34.1% falls between the mean and one standard deviation below the mean. - This is a fundamental property derived from the **empirical rule (68-95-99.7 rule)**, where 68% of the data lies within one standard deviation of the mean (34% on each side). *15%* - This percentage is too low and does not align with the properties of a **standard normal distribution** regarding the area between the mean and one standard deviation. - While 15.85% of data falls *beyond* one standard deviation above or below the mean, it's not the area *between* the mean and one standard deviation. *68%* - This value represents the total area under the curve that lies within **one standard deviation** *of the mean* (i.e., from -1 SD to +1 SD from the mean). - It is the sum of the areas between the mean and +1 SD, and between the mean and -1 SD, which is 34% + 34% = 68%. The question specifically asks for the area between the mean and *one* standard deviation (i.e., on one side). *95%* - This value represents the total area under the curve that lies within **two standard deviations** *of the mean* (i.e., from -2 SD to +2 SD from the mean). - According to the **empirical rule**, approximately 95% of data falls within two standard deviations of the mean.

Q: Case-control study is an example of?

Retrospective study. ***Retrospective study*** - In a **case-control study**, researchers look back in time to identify past exposures that may have led to a disease or outcome. - They start with an outcome (cases) and then investigate their past exposures, comparing them to a control group free of the outcome. *Prospective study* - A **prospective study** follows participants forward in time to observe the development of an outcome after an exposure. - Examples include cohort studies, where groups are followed over time to see who develops a disease. *Combined retrospective and prospective study* - This option refers to study designs that incorporate elements of both backward and forward-looking data collection. - While some complex study designs can have both components, a pure case-control study is primarily retrospective. *Study at one point of time* - This describes a **cross-sectional study**, which measures exposure and outcome simultaneously at a single point in time. - Case-control studies, by contrast, involve looking back in time to assess past exposures relative to a current outcome.

Q: Which type of chart is best to represent the following data? Year: 1991, 1992, 1993, 1994; Number of LBW babies: 125, 50, 25, 75.

Bar chart. **Bar chart** - A **bar chart** is the most appropriate for representing categorical data or discrete numerical data over a period. - Each year (1991, 1992, 1993, 1994) represents a distinct category, and the number of LBW babies is the quantitative value associated with each year. *Histogram* - A **histogram** is used to represent the distribution of continuous numerical data, grouped into bins, to show frequencies. - The data provided (years and counts) is discrete, not continuous. *Frequency polygon* - A **frequency polygon** is used to display the shape of distribution for a continuous variable, often by connecting the midpoints of the tops of the bars in a histogram. - It is not suitable for discrete yearly data, as there are no continuous intervals to connect. *Scatter diagram* - A **scatter diagram** is used to show the relationship or correlation between two continuous numerical variables. - While one variable is numerical (number of LBW babies), the other (year) is categorical or ordinal, and the primary purpose here is to show change over time, not a correlation between two continuous variables.

Q: What is the numerator in the formula for calculating Negative Predictive Value (NPV) in diagnostic testing?

True negative. ***True negative*** - In the calculation of **Negative Predictive Value (NPV)**, the numerator represents the number of individuals who are truly disease-free and also test negative for the disease. - NPV answers the question: "If a patient tests negative, what is the probability that they are actually **disease-free**?" *True positive* - **True positives** are individuals who have the disease and also test positive; they are the numerator for **Positive Predictive Value (PPV)**. - They do not factor into the numerator for NPV, which focuses on negative test results and the absence of disease. *False positive* - **False positives** are individuals who do not have the disease but test positive; they are found in the denominator for PPV, but not in the numerator for NPV. - They represent an incorrect test result and do not contribute to the count of truly healthy individuals with a negative test. *False negative* - **False negatives** are individuals who have the disease but test negative; they are in the denominator for **sensitivity** and NPV. - They represent a missed diagnosis and are not part of the numerator for NPV, which specifically identifies correctly identified healthy individuals.

Question 1

Which of the following is NOT a characteristic of a health index?

Accepted Answer

Affordability

Answer

Validity

Answer

Reliability

Answer

Feasibility

Question 2

In a study a patient does not know the nature of drug [whether a placebo or curative drug] he is taking. The researcher knows the drug type to be given to the individuals in study. Type of blinding in this study is?

Accepted Answer

Single

Answer

Double

Answer

Triple

Answer

Combined double/triple

Question 3

Which of the following is a parametric test?

Accepted Answer

Student t-test

Answer

Sign test

Answer

Fisher exact test

Answer

Chi-square test

Question 4

Sensitivity of a screening test tells about

Accepted Answer

Percentage of individuals with the disease who test positive.

Answer

Percentage of healthy individuals among those with a negative test result.

Answer

Percentage of individuals with the disease among those with a positive test result.

Answer

Percentage of healthy individuals among those with a positive test result.

Question 5

In a positively skewed distribution, which of the following is true?

Accepted Answer

Mean > Median > Mode

Answer

Mean = Median = Mode

Answer

Mode > Median > Mean

Answer

None of the options

Question 6

The figure below represents a statistical distribution. What type of skewness does it exhibit?

Accepted Answer

Right skewed

Answer

Normal distribution

Answer

Left skewed

Answer

Bimodal distribution

Question 7

In a standard normal distribution curve, what percentage of the area under the curve lies between the mean and one standard deviation from the mean?

Accepted Answer

34%

Answer

68%

Answer

15%

Answer

95%

Question 8

Case-control study is an example of?

Accepted Answer

Retrospective study

Answer

Prospective study

Answer

Combined retrospective and prospective study

Answer

Study at one point of time

Question 9

Which type of chart is best to represent the following data? Year: 1991, 1992, 1993, 1994; Number of LBW babies: 125, 50, 25, 75.

Accepted Answer

Bar chart

Answer

Histogram

Answer

Scatter diagram

Answer

Frequency polygon

Question 10

What is the numerator in the formula for calculating Negative Predictive Value (NPV) in diagnostic testing?

Accepted Answer

True negative

Answer

True positive

Answer

False positive

Answer

False negative

Biostatistics — MCQs

Biostatistics — MCQs

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