Biostatistics Practice Questions

Q: For a population of 10,000, what does a sex ratio of more than 1000 indicate?

Males are less than 5000. ### Explanation **1. Understanding the Concept** In Indian Demography and Biostatistics, the **Sex Ratio** is defined as the number of females per 1,000 males. * **Formula:** (Number of Females / Number of Males) × 1,000 If the sex ratio is **more than 1,000**, it mathematically implies that the numerator (Females) is greater than the denominator (Males). * In a population of 10,000, if the ratio is exactly 1,000, there are 5,000 males and 5,000 females. * If the ratio is **>1,000**, females must be **>5,000** and males must be **<5,000**. Therefore, Option D is the correct logical conclusion. **2. Analysis of Incorrect Options** * **Option A & B:** These options suggest a total population count far below the given 10,000. If males or females were less than 500, the other gender would have to be over 9,500, which is an extreme outlier and does not specifically define a ratio "more than 1,000." * **Option C:** If females were less than 5,000 in a population of 10,000, the males would be more than 5,000. This would result in a sex ratio of **less than 1,000** (a deficit of females), which contradicts the question. **3. High-Yield Clinical Pearls for NEET-PG** * **Child Sex Ratio:** Calculated for the 0–6 years age group. * **Global vs. Indian Definition:** In most Western countries, the sex ratio is expressed as males per 100 females. However, for NEET-PG, always follow the **Indian Census definition**: Females per 1,000 males. * **Highest Sex Ratio (Census 2011):** Kerala (1,084). * **Lowest Sex Ratio (Census 2011):** Haryana (879). * **Overall India Sex Ratio (Census 2011):** 943.

Q: Which statistical test is used for counting the direction of differences within a paired sample?

Sign test. ### Explanation **Correct Answer: D. Sign test** The **Sign test** is a non-parametric test used to analyze the **direction of differences** between paired observations (e.g., "before and after" measurements). It focuses solely on whether the difference is positive (+) or negative (-) rather than the actual magnitude of the change. It is used when the data is ordinal or when the distribution of differences is not normal, making it the simplest test for paired data. **Why other options are incorrect:** * **A. t-test (Paired):** This is a parametric test used for paired samples. Unlike the Sign test, it requires the data to be on an interval/ratio scale and assumes a **normal distribution**. It considers the magnitude of the difference, not just the direction. * **B. Z-test:** This is used for large samples (n > 30) to compare means or proportions. It is not specifically designed for "counting directions" in paired samples. * **C. F-test (ANOVA):** This test is used to compare the **variances** of two populations or to compare means among three or more groups. It does not analyze paired directional differences. **High-Yield Clinical Pearls for NEET-PG:** * **Sign Test vs. Wilcoxon Signed-Rank Test:** While both are non-parametric tests for paired data, the Sign test only looks at the **direction** (+/-), whereas the Wilcoxon Signed-Rank test considers both the **direction and the magnitude** (ranks). * **Non-Parametric Equivalents:** * Unpaired t-test → Mann-Whitney U test. * Paired t-test → Wilcoxon Signed-Rank test or Sign test. * One-way ANOVA → Kruskal-Wallis test. * **Rule of Thumb:** If the question mentions "direction only" or "nominal/ordinal paired data," think **Sign Test**.

Q: In the presence of unusually high outliers, which is the preferred measure of central tendency?

Median. ### Explanation **1. Why Median is the Correct Answer:** In biostatistics, the **Median** is the "positional average" that divides a distribution into two equal halves. Its primary advantage is that it is **robust to outliers** (extreme values). When a dataset contains unusually high or low values, the distribution becomes **skewed**. While the Mean is pulled toward the tail of the skew, the Median remains stable because it depends on the rank order of observations rather than their numerical magnitude. Therefore, for skewed data, the Median provides a more accurate representation of the "typical" value. **2. Analysis of Incorrect Options:** * **A. Mean:** This is the arithmetic average. It is highly sensitive to outliers because every value in the dataset is used in its calculation. A single extreme outlier can significantly inflate or deflate the Mean, making it a poor measure for skewed distributions. * **B. Mode:** This is the most frequently occurring value. While it is not affected by outliers, it is often unstable (a dataset can be bimodal or have no mode at all), making it less reliable than the Median for general central tendency. * **D. Range:** This is a measure of **dispersion** (spread), not central tendency. It is calculated as the difference between the maximum and minimum values and is, in fact, the measure *most* affected by outliers. **3. High-Yield Clinical Pearls for NEET-PG:** * **Normal Distribution:** Mean = Median = Mode. * **Positive Skew (Right-tailed):** Mean > Median > Mode (e.g., income levels, incubation periods). * **Negative Skew (Left-tailed):** Mode > Median > Mean (e.g., age at death in developed countries). * **Best measure for Nominal data:** Mode. * **Best measure for Ordinal data:** Median. * **Best measure for Interval/Ratio data (No outliers):** Mean.

Q: In a population, the total number of births in a year is 3050. There are 50 stillbirths, 100 neonatal deaths within the first 7 days, and 150 deaths between the 8th and 28th day of life. Calculate the Neonatal Mortality Rate.

83. ### Explanation **1. Understanding the Correct Answer (C: 83)** To calculate the **Neonatal Mortality Rate (NMR)**, we must understand its definition: the number of deaths of live-born infants during the first 28 completed days of life per 1,000 live births. * **Step 1: Identify Live Births.** The question gives "Total Births" (3050) and "Stillbirths" (50). Since Live Births = Total Births – Stillbirths, we have: $3050 - 50 = 3000$ live births. * **Step 2: Identify Neonatal Deaths.** This includes both Early Neonatal Deaths (0-7 days) and Late Neonatal Deaths (8-28 days). Total deaths = $100 + 150 = 250$. * **Step 3: Apply Formula.** $$\text{NMR} = \frac{\text{Total Neonatal Deaths}}{\text{Total Live Births}} \times 1000$$ $$\text{NMR} = \frac{250}{3000} \times 1000 = \frac{250}{3} \approx \mathbf{83.33}$$ **2. Why Other Options are Incorrect** * **Option A (250):** This is the absolute number of neonatal deaths, not the rate per 1,000 live births. * **Option B (100):** This only accounts for Early Neonatal Deaths (0-7 days). * **Option D (90):** This is a distractor resulting from calculation errors or using the wrong denominator (e.g., using total births instead of live births). **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Denominator Rule:** Most mortality rates in the first year of life (Infant, Neonatal, Post-neonatal) use **Live Births** as the denominator. The **Perinatal Mortality Rate** is a notable exception that uses **Total Births** (Live births + Stillbirths). * **Early vs. Late:** Early Neonatal Mortality (0-7 days) reflects maternal health and quality of obstetric care, while Late Neonatal Mortality (8-28 days) often reflects environmental factors and infections. * **Current Trend:** In India, Neonatal Mortality accounts for approximately **70% of the Infant Mortality Rate (IMR)**, making it the most critical target for reducing under-5 mortality.

Q: Mean hemoglobin values are compared between two independent population groups. What is the most appropriate statistical test to use?

Unpaired T-test. To select the correct statistical test, we must evaluate the **type of data** and the **number of groups** being compared. ### 1. Why Unpaired T-test is Correct The question involves comparing **Mean Hemoglobin values**, which is **quantitative (numerical/continuous) data**. These values are being compared between **two independent population groups** (e.g., males vs. females or Group A vs. Group B). * The **Unpaired T-test** (also known as the Independent Samples T-test) is specifically designed to compare the means of two independent groups when the data follows a normal distribution. ### 2. Why Other Options are Incorrect * **Paired T-test:** Used for quantitative data when the two sets of observations are related (e.g., "Before and After" treatment measurements in the same individual). * **Chi-square test:** Used for **qualitative (categorical) data** to compare proportions or associations (e.g., comparing the percentage of anemic vs. non-anemic patients between two groups). * **Fisher's exact test:** Also used for qualitative data, specifically when the sample size is small (e.g., any cell value in a 2x2 table is less than 5). ### 3. NEET-PG High-Yield Pearls * **Rule of Thumb:** If the data is **Quantitative**, use a **T-test** (2 groups) or **ANOVA** (>2 groups). If the data is **Qualitative**, use **Chi-square**. * **Z-test:** Used instead of a T-test if the sample size is large (**n > 30**). * **Non-parametric equivalent:** If the data is not normally distributed, the **Mann-Whitney U test** is the non-parametric alternative to the Unpaired T-test.

Q: Two groups are tested for anemia. Which statistical test should be used?

Chi-square test. ### Explanation The key to selecting the correct statistical test lies in identifying the **type of data** being analyzed. **Why Chi-square test is correct:** In this scenario, "anemia" is a **qualitative (categorical) variable**. When testing for anemia, individuals are classified into categories: "Anemic" or "Non-anemic." When comparing two independent groups (e.g., Group A vs. Group B) based on a categorical outcome, we use a **contingency table** (2x2 table) and apply the **Chi-square test**. It assesses the significance of the difference between observed and expected frequencies. **Why the other options are incorrect:** * **Paired T-test:** Used for **quantitative (numerical)** data when comparing means of the *same* group at two different times (e.g., hemoglobin levels before and after treatment). * **Unpaired (Independent) T-test:** Used for **quantitative** data when comparing the means of *two* different groups (e.g., comparing the mean Hemoglobin value in g/dL between Group A and Group B). * **ANOVA (Analysis of Variance):** Used for **quantitative** data when comparing the means of *three or more* groups. **Clinical Pearls for NEET-PG:** * **Categorical Data (Proportions/Percentages) →** Chi-square test. * **Numerical Data (Means/SD) →** T-test (for 2 groups) or ANOVA (for >2 groups). * If the sample size is very small (any cell value in a 2x2 table is <5), use **Fisher’s Exact Test** instead of Chi-square. * **Correlation coefficient (r)** measures the strength of a linear relationship between two numerical variables, while **Regression** predicts the value of one variable based on another.

Q: Which of the following is an example of a nominal variable?

Roll number. **Explanation:** In biostatistics, variables are classified based on their level of measurement. A **Nominal variable** is a type of qualitative (categorical) data where numbers or names are used solely as labels to identify or categorize items. There is no inherent numerical value, order, or rank associated with these labels. * **Why Roll Number is correct:** Although a roll number consists of digits, it is a **Nominal variable**. It serves only as a unique identifier for a student. You cannot perform meaningful mathematical operations on it (e.g., adding two roll numbers is meaningless), nor does a higher roll number imply "more" of a specific attribute. Other examples include Gender, Blood Group, and Marital Status. **Analysis of Incorrect Options:** * **Temperature (Option A):** This is a **Scale/Interval variable**. It is quantitative data where the distance between points is equal, but there is no "absolute zero" (0°C does not mean absence of heat). * **TNM Staging (Option C):** This is an **Ordinal variable**. While it is categorical, there is a clear, inherent rank or progression (Stage II is more advanced than Stage I). * **Mid-arm circumference (Option D):** This is a **Ratio variable** (Continuous quantitative data). It has a defined absolute zero and can be measured in decimals. **High-Yield Clinical Pearls for NEET-PG:** * **NOIR Hierarchy:** Remember the hierarchy from simplest to most complex: **N**ominal < **O**rdinal < **I**nterval < **R**atio. * **Qualitative Data:** Includes Nominal and Ordinal. * **Quantitative Data:** Includes Interval and Ratio (Discrete or Continuous). * **Visual Aid:** If you can rank the data, it's **Ordinal**; if it's just a name/label, it's **Nominal**.

Question 1

For a population of 10,000, what does a sex ratio of more than 1000 indicate?

Accepted Answer

Males are less than 5000

Answer

Males are less than 500

Answer

Females are less than 500

Answer

Females are less than 5000

Question 2

Which statistical test is used for counting the direction of differences within a paired sample?

Accepted Answer

Sign test

Answer

t test

Answer

Z test

Answer

F test

Question 3

In the presence of unusually high outliers, which is the preferred measure of central tendency?

Accepted Answer

Median

Answer

Mean

Answer

Mode

Answer

Range

Question 4

In a population, the total number of births in a year is 3050. There are 50 stillbirths, 100 neonatal deaths within the first 7 days, and 150 deaths between the 8th and 28th day of life. Calculate the Neonatal Mortality Rate.

Accepted Answer

83

Answer

250

Answer

100

Answer

90

Question 5

ELISA is performed on a population with low prevalence. What would be the result of performing double screening ELISA tests?

Accepted Answer

Increased specificity and positive predictive value

Answer

Increased sensitivity and positive predictive value

Answer

Increased sensitivity and negative predictive value

Answer

Increased specificity and negative predictive value

Question 6

Mean hemoglobin values are compared between two independent population groups. What is the most appropriate statistical test to use?

Accepted Answer

Unpaired T-test

Answer

Paired T-test

Answer

Chi-square test

Answer

Fisher's exact test

Question 7

Two groups are tested for anemia. Which statistical test should be used?

Accepted Answer

Chi-square test

Answer

Paired T-test

Answer

Unpaired T-test

Answer

ANOVA

Question 8

A test to measure blood pressure has successive readings for the same person as follows: 110/70 mmHg, 128/80 mmHg, 132/70 mmHg, 160/90 mmHg. The given test has a mean blood pressure of 120/80 mmHg. What can be concluded about the test's validity and reliability?

Accepted Answer

Low validity, Low reliability

Answer

Low validity, high reliability

Answer

High validity, low reliability

Answer

High validity, high reliability

Question 9

General fertility rate is a better measure of fertility than the crude birth rate because the denominator includes which of the following?

Accepted Answer

Females aged 15-45 years

Answer

Midyear population

Answer

Total female population

Answer

Married female population

Question 10

Which of the following is an example of a nominal variable?

Accepted Answer

Roll number

Answer

Temperature

Answer

TNM staging

Answer

Mid-arm circumference

Biostatistics — MCQs

Biostatistics — MCQs

On this page

Practice by Chapter

Want unlimited practice?