Biostatistics Practice Questions

Q: Which of the following properties is NOT possessed by an interval variable?

True zero. In biostatistics, variables are classified into four levels of measurement (NOIR: Nominal, Ordinal, Interval, and Ratio). Understanding the hierarchy of these scales is crucial for selecting appropriate statistical tests. **Explanation of the Correct Answer:** The correct answer is **D (True zero)**. An **Interval scale** possesses identity, magnitude, and equal intervals between values, but it lacks an **absolute or "true" zero**. In an interval scale, zero is arbitrary and does not represent the total absence of the quantity being measured. * *Example:* Temperature in Celsius. 0°C does not mean "no temperature"; it is simply a point on the scale. Because there is no true zero, you cannot say 40°C is "twice as hot" as 20°C. A true zero is only found in **Ratio scales** (e.g., Height, Weight, BP). **Analysis of Incorrect Options:** * **A. Identity:** This is the most basic property (found in Nominal scales). it means different numbers represent different categories (e.g., Male=1, Female=2). * **B. Magnitude:** This means the numbers have a relative order or rank (found in Ordinal scales). One value can be identified as greater than or less than another. * **C. Equidistance:** This is the hallmark of the Interval scale. The physical distance between 10 and 20 is exactly the same as between 30 and 40. **High-Yield Clinical Pearls for NEET-PG:** * **NOIR Mnemonic:** **N**ominal (Name only), **O**rdinal (Order/Rank), **I**nterval (Equal distance), **R**atio (True zero). * **IQ Scores and Temperature (C/F):** Classic examples of Interval scales. * **Kelvin Scale:** Unlike Celsius, Kelvin is a **Ratio scale** because 0 K represents absolute zero (no molecular motion). * **Statistical Test Rule:** For Interval and Ratio data, use **Parametric tests** (e.g., t-test, ANOVA) if normally distributed. For Nominal and Ordinal data, use **Non-parametric tests** (e.g., Chi-square, Mann-Whitney U).

Q: In a population of 10,000 people, there were 200 deaths in a year. Out of those, 40 died due to HIV. What is the proportional mortality rate from HIV?

20%. ### **Explanation** The correct answer is **20%**. **Understanding the Concept:** Proportional Mortality Rate (PMR) is a measure of the relative importance of a specific cause of death within a population. Unlike mortality rates that use the total population as a denominator, PMR expresses the number of deaths due to a particular cause as a percentage of the **total deaths** from all causes during the same period. **Calculation:** $$\text{Proportional Mortality Rate} = \frac{\text{Deaths due to a specific cause (HIV)}}{\text{Total deaths from all causes}} \times 100$$ $$\text{PMR} = \frac{40}{200} \times 100 = 20\%$$ --- ### **Analysis of Options:** * **Option B (20%) is Correct:** It correctly uses the total number of deaths (200) as the denominator. * **Option A (10%):** This is a calculation error, likely from misinterpreting the ratio. * **Option C (0.40%):** This represents the **Cause-Specific Mortality Rate** (Deaths from HIV / Total Population $\times$ 100). While a valid statistic ($40/10,000$), it is not the *proportional* mortality. * **Option D (0.20%):** This represents the **Crude Death Rate** (Total Deaths / Total Population $\times$ 100), which is $200/10,000$. --- ### **High-Yield Clinical Pearls for NEET-PG:** * **Denominator Check:** Always look at the denominator. If it’s "Total Deaths," it is Proportional Mortality. If it’s "Total Cases of that disease," it is Case Fatality Rate (CFR). If it’s "Total Mid-year Population," it is a Mortality Rate. * **PMR vs. CFR:** PMR indicates the "burden" of a disease in terms of total mortality, whereas Case Fatality Rate (CFR) indicates the "killing power" or virulence of a disease. * **PMR Use:** It is particularly useful when population data (denominator) is unavailable, but death records are accessible. It is not a measure of the risk of dying from a disease.

Q: In Infant Mortality Rate (IMR), what is the age range considered for an infant?

Below 1 year. **Explanation:** **1. Why "Below 1 year" is correct:** In public health and biostatistics, an **Infant** is defined as a child from birth up to (but not including) the first birthday. The **Infant Mortality Rate (IMR)** is calculated as the number of deaths of children under one year of age per 1,000 live births in a given year. Mathematically, this is expressed as: *(Number of deaths under 1 year of age / Total number of live births) × 1000.* **2. Why the other options are incorrect:** * **Option A (Below 1 month):** This refers to the **Neonatal** period. Deaths in this range contribute to the Neonatal Mortality Rate (NMR), which is a subset of IMR. * **Option C (Up to 1 year):** While semantically similar, "below 1 year" is the precise technical definition used by the WHO and SRS (Sample Registration System). "Up to 1 year" can be ambiguous as to whether it includes the 365th day or the entire 12th month. * **Option D (28 days):** This is the specific cutoff for the **Neonatal period** (0–28 days). Deaths occurring after 28 days but before 1 year are termed "Post-neonatal" deaths. **3. High-Yield Clinical Pearls for NEET-PG:** * **IMR is the most sensitive index** of the health status of a community and the level of socio-economic development. * **Current IMR of India (SRS 2020):** 28 per 1000 live births. * **Components of IMR:** IMR = Neonatal Mortality (0–28 days) + Post-Neonatal Mortality (28 days to 1 year). * **Commonest cause of IMR in India:** Low Birth Weight (LBW) and Prematurity, followed by Pneumonia and Diarrheal diseases.

Q: A physician, after examining a group of patients with a certain disease, classifies the condition of each one as 'Normal', 'Mild', 'Moderate', or 'Severe'. Which one of the following is the scale of measurement being adopted for classification of the disease condition?

Ordinal. ### Explanation The correct answer is **Ordinal** because the classification of disease severity (Normal, Mild, Moderate, Severe) involves categories that follow a **natural, logical order or rank**, but the mathematical distance between these ranks is not uniform or quantifiable. #### 1. Why Ordinal is Correct In biostatistics, the **Ordinal scale** is used for data that can be ranked. In this clinical scenario, 'Severe' is clearly worse than 'Moderate', which is worse than 'Mild'. However, we cannot mathematically state that the difference between 'Mild' and 'Moderate' is exactly the same as the difference between 'Moderate' and 'Severe'. Common medical examples include Cancer Staging (I, II, III, IV) and the Glasgow Coma Scale (GCS). #### 2. Why Other Options are Incorrect * **Nominal:** This scale is for naming categories without any inherent order (e.g., Gender, Blood Group, or Color of eyes). Since disease severity has a clear "better-to-worse" hierarchy, it is not nominal. * **Interval:** This scale has a defined order and equal intervals between values, but **no absolute zero** (e.g., Temperature in Celsius). Disease severity lacks these precise, equal mathematical intervals. * **Ratio:** This is the highest level of measurement. it has equal intervals and a **true absolute zero** (e.g., Height, Weight, Blood Pressure). You cannot have a "zero" severity in a way that allows for ratios (e.g., you can't say 'Severe' is exactly four times 'Mild'). #### Clinical Pearls for NEET-PG * **Mnemonic (NOIR):** **N**ominal < **O**rdinal < **I**nterval < **R**atio (from simplest to most complex). * **Qualitative Data:** Includes Nominal and Ordinal scales. * **Quantitative Data:** Includes Interval and Ratio scales. * **Visual Analogue Scale (VAS)** for pain is a classic example of **Ordinal** data often tested in exams. * **Likert Scales** (Strongly agree to Strongly disagree) are always **Ordinal**.

Q: What is the median value for the following data set: 5, 5, 50, 150, 10, 20?

15. ### Explanation **1. Why Option A is Correct:** The **Median** is the middle-most value of a data set when the observations are arranged in ascending or descending order. It is a measure of central tendency that is particularly useful for skewed data. To find the median for the given data set (5, 5, 50, 150, 10, 20): * **Step 1: Arrange in ascending order:** 5, 5, 10, 20, 50, 150. * **Step 2: Identify the number of observations (n):** Here, $n = 6$ (an even number). * **Step 3: Apply the formula for even $n$:** The median is the average of the two middle terms, specifically the $(\frac{n}{2})^{th}$ and $(\frac{n}{2} + 1)^{th}$ values. * $\frac{6}{2} = 3^{rd}$ value (which is 10) * $\frac{6}{2} + 1 = 4^{th}$ value (which is 20) * **Step 4: Calculate the average:** $\frac{10 + 20}{2} = \mathbf{15}$. **2. Why Other Options are Incorrect:** * **Option B (10):** This is the $3^{rd}$ value in the ordered sequence. It would only be the median if there were 5 observations. * **Option C (20):** This is the $4^{th}$ value. Selecting this ignores the rule for calculating the average of the two middle terms in an even-numbered set. * **Option D (40):** This value is mathematically unrelated to the median calculation for this specific set. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Robustness:** The Median is the best measure of central tendency for **skewed distributions** because it is not influenced by extreme values (outliers), unlike the Mean. * **Relationship in Skewed Data:** * **Positively Skewed:** Mean > Median > Mode. * **Negatively Skewed:** Mode > Median > Mean. * **Calculation Tip:** If $n$ is odd, the median is simply the middle value: $(\frac{n+1}{2})^{th}$ observation. * **Graphical Representation:** The median can be determined graphically using an **Ogive** (Cumulative Frequency Curve).

Q: The formula denotes:

Specificity. ***Specificity*** - The formula **TN/(TN+FP)** represents specificity, which measures a test's ability to correctly identify **true negatives** (disease-free individuals). - Specificity indicates the proportion of **healthy individuals** correctly identified as negative by the test. *Sensitivity* - Sensitivity uses the formula **TP/(TP+FN)**, measuring a test's ability to correctly identify **true positives** (diseased individuals). - It represents the proportion of **sick individuals** correctly identified as positive, not the given formula. *Positive Predictive Value* - PPV uses the formula **TP/(TP+FP)**, indicating the probability that a **positive test result** truly represents disease. - It focuses on **true positives** among all positive results, different from the specificity formula given. *Negative Predictive Value* - NPV uses the formula **TN/(TN+FN)**, indicating the probability that a **negative test result** truly represents absence of disease. - While it includes **TN** in the numerator, the denominator differs by including **false negatives** instead of false positives.

Q: The male to female ratio is typically expressed as:

Number of females per 1000 males. ### Explanation **1. Understanding the Correct Answer (Option B)** In biostatistics and demography, the **Sex Ratio** is a measure used to describe the gender balance in a population. In India, the standard convention followed by the Census is to express the sex ratio as the **number of females per 1,000 males**. This is a specific type of "Ratio" where the numerator (females) is not a part of the denominator (males), and the multiplier is 1,000. **2. Analysis of Incorrect Options** * **Option A:** "Number of males per 1000 population" describes a **Proportion** (where the numerator is part of the denominator), not a ratio. * **Option C:** "Number of males per 1000 females" is the international convention used by the United Nations and many Western countries. However, in the context of Indian medical exams (NEET-PG/INI-CET) and the Indian Census, the definition is strictly the inverse (Females/Males). * **Option D:** Incorrect, as Option B is the standard demographic definition in India. **3. High-Yield Clinical Pearls for NEET-PG** * **Child Sex Ratio (CSR):** Defined as the number of girls per 1,000 boys in the **0–6 year** age group. * **Latest Data (NFHS-5):** For the first time, the National Family Health Survey-5 reported a sex ratio of **1,020 females per 1,000 males** (though Census data remains the gold standard for official figures). * **Census 2011 Data:** The official Sex Ratio of India was **943** females per 1,000 males, and the Child Sex Ratio was **919**. * **Key Distinction:** Remember that **Ratio** compares two independent groups (e.g., Male:Female), whereas **Rate** involves a time dimension, and **Proportion** expresses a part of the whole.

Question 1

When launching a study, many respondents are invited, some of whom fail to come. This phenomenon is called?

Accepted Answer

Response bias

Answer

Volunteer bias

Answer

Selection bias

Answer

Berksonian bias

Question 2

Which of the following properties is NOT possessed by an interval variable?

Accepted Answer

True zero

Answer

Identity

Answer

Magnitude

Answer

Equidistance

Question 3

In a population of 10,000 people, there were 200 deaths in a year. Out of those, 40 died due to HIV. What is the proportional mortality rate from HIV?

Accepted Answer

20%

Answer

10%

Answer

0.40%

Answer

0.20%

Question 4

In Infant Mortality Rate (IMR), what is the age range considered for an infant?

Accepted Answer

Below 1 year

Answer

Below 1 month

Answer

Up to 1 year

Answer

28 days

Question 5

A physician, after examining a group of patients with a certain disease, classifies the condition of each one as 'Normal', 'Mild', 'Moderate', or 'Severe'. Which one of the following is the scale of measurement being adopted for classification of the disease condition?

Accepted Answer

Ordinal

Answer

Nominal

Answer

Interval

Answer

Ratio

Question 6

What is the denominator used for calculating the GFR (Glomerular Filtration Rate)?

Accepted Answer

Females aged 15-44 years

Answer

Mid-year population

Answer

Married females

Answer

None of the above

Question 7

What sampling method is used in assessing the immunization status of children under an immunization program?

Accepted Answer

Cluster sampling

Answer

Systematic sampling

Answer

Stratified sampling

Answer

Group sampling

Question 8

What is the median value for the following data set: 5, 5, 50, 150, 10, 20?

Accepted Answer

15

Answer

10

Answer

20

Answer

40

Question 9

The formula denotes:

Accepted Answer

Specificity

Answer

Sensitivity

Answer

Positive Predictive Value

Answer

Negative Predictive Value

Question 10

The male to female ratio is typically expressed as:

Accepted Answer

Number of females per 1000 males

Answer

Number of males per 1000 population

Answer

Number of males per 1000 females

Answer

None of the above

Biostatistics — MCQs

Biostatistics — MCQs

On this page

Practice by Chapter

Want unlimited practice?