Biostatistics

Biostatistics Indian Medical PG Question 1: Which one of the following is not a measure of dispersion?

• A. Mean deviation
• B. Standard deviation
• C. Range
• D. Mean (Correct Answer)

Biostatistics Explanation: ***Mean*** - The **mean** is a measure of **central tendency**, representing the average value of a dataset. - It describes the typical value around which data points cluster, rather than how spread out they are. *Mean deviation* - **Mean deviation** is a measure of **dispersion** that calculates the average of the absolute differences between each data point and the mean of the dataset. - It quantifies the average deviation of data points from the center. *Standard deviation* - **Standard deviation** is a widely used measure of **dispersion** that indicates the average amount of variability or spread around the mean. - A higher standard deviation suggests data points are more spread out from the mean. *Range* - The **range** is a simple measure of **dispersion** calculated as the difference between the highest and lowest values in a dataset. - It provides a basic idea of the total spread of data from its extremes.

Biostatistics Indian Medical PG Question 2: You have diagnosed a patient clinically as having SLE and ordered 6 tests out of which 4 tests have come positive and 2 are negative. Which of the following values are required to determine the probability of SLE at this point?

• A. Relative risk of SLE in the patient
• B. Incidence and prevalence of SLE
• C. Prior probability of SLE, sensitivity and specificity of each test (Correct Answer)
• D. Incidence of SLE and the predictive value of each test

Biostatistics Explanation: ***Prior probability of SLE, sensitivity and specificity of each test*** - To determine the **post-test probability** of a disease like SLE, you need the **prior probability** (pre-test probability) of the disease in the patient. - Additionally, the **sensitivity** (true positive rate) and **specificity** (true negative rate) of *each* diagnostic test are crucial for calculating how much each positive or negative test result alters that prior probability, often using **Bayes' theorem**. *Relative risk of SLE in the patient* - **Relative risk** is a measure of association between exposure and disease, typically used in **epidemiological studies** to compare risk in exposed vs. unexposed groups. - It does not directly help determine an individual patient's post-test probability of SLE based on their specific test results. *Incidence and prevalence of SLE* - **Incidence** refers to the rate of new cases in a population over a specific period, while **prevalence** refers to the proportion of individuals in a population who have the disease at a specific time. - While prevalence can contribute to the **prior probability** for a general population, it's not sufficient on its own, nor does it incorporate the results of individual diagnostic tests. *Incidence of SLE and the predictive value of each test* - Although **predictive values (positive and negative)** are important for interpreting test results, they are *derived from* sensitivity, specificity, and prevalence. - To *determine* the probability of SLE using multiple tests, you need the fundamental properties of the tests (sensitivity and specificity) and the prior probability, rather than just the incidence and already-calculated predictive values.

Biostatistics Indian Medical PG Question 3: Which study design is most effective for investigating rare adverse effects of a drug?

• A. Cohort study
• B. Cross-sectional study
• C. Case-control study (Correct Answer)
• D. Clinical trial/experimental study

Biostatistics Explanation: ***Case-control study*** - This design starts by identifying individuals with the **rare adverse effect (cases)** and a control group without the effect to look back for exposure to the drug. - It is efficient for studying rare outcomes because it doesn't require following a large population for a long time to observe few events. *Cohort study* - A **cohort study** follows a group of individuals exposed and unexposed to a drug forward in time to observe outcomes. - While good for common outcomes, it would require an **extremely large sample size** and a long follow-up period to observe rare adverse drug effects. *Cross-sectional study* - A **cross-sectional study** assesses exposure and outcome simultaneously at a single point in time. - This design is suitable for determining **prevalence** but cannot establish temporal relationships between drug exposure and rare adverse effects, nor is it efficient for rare outcomes. *Clinical trial/experimental study* - **Clinical trials** are primarily designed to test the efficacy and safety of new interventions, usually focusing on common adverse effects. - They are generally **not powered** or long enough to detect rare adverse events, as such events would occur in very few participants, if any.

Biostatistics Indian Medical PG Question 4: International prognostic index for lymphomas includes the following prognostic factors, EXCEPT:

• A. LDH
• B. Number of extralymphatic sites involved
• C. Hemoglobin and albumin (Correct Answer)
• D. Stage of disease

Biostatistics Explanation: ***Hemoglobin and albumin*** - While hemoglobin and albumin can be indicators of overall health and nutritional status, they are **not part of the standard International Prognostic Index (IPI)** for lymphomas. - The IPI specifically focuses on factors directly related to tumor burden and patient vitality, not general systemic markers like these. *LDH* - **Lactate dehydrogenase (LDH)** is a crucial component of the IPI, reflecting tumor burden and aggressiveness [1]. - Elevated LDH levels indicate a higher risk and are associated with a poorer prognosis [1]. *Number of extralymphatic sites involved* - The **number of extralymphatic sites involved** is a key prognostic factor in the IPI. - Involvement of more than one extralymphatic site indicates more widespread disease and a worse prognosis. *Stage of disease* - The **stage of disease**, as defined by the Ann Arbor staging system, is an essential element of the IPI [1]. - Advanced stages (III or IV) are associated with a poorer prognosis compared to early stages [1].

Biostatistics Indian Medical PG Question 5: The appropriate statistical test to find out obesity as a significant risk factor for breast cancer is:

• A. Chi-square test (Correct Answer)
• B. Wilcoxon’s signed rank test
• C. Student’s paired ‘t’ test
• D. Student’s unpaired ‘t’ test

Biostatistics Explanation: ***Chi-square test*** - The **chi-square test** is used to determine if there is a **significant association** between two **categorical variables**. - In this scenario, both obesity (yes/no) and breast cancer (yes/no) are categorical, making chi-square appropriate to assess if obesity is a risk factor. *Wilcoxon’s signed rank test* - This is a **non-parametric test** used for comparing two related samples or repeated measurements on a single sample, especially when data are not normally distributed. - It is not suitable for assessing the association between two independent categorical variables like obesity and breast cancer. *Student’s paired ‘t’ test* - The **paired t-test** is used to compare the means of two related groups or measurements from the same subject under different conditions (e.g., before and after an intervention). - This test is designed for **continuous data** and would not be appropriate for the categorical variables of obesity and breast cancer. *Student’s unpaired ‘t’ test* - The **unpaired t-test** (also known as independent samples t-test) is used to compare the means of two independent groups for a **continuous outcome variable**. - It is not suitable when both the exposure (obesity) and the outcome (breast cancer) are categorical variables.

Biostatistics Flashcard 1 of 5

Question: Calculating one variable using another variable is done using coefficient of _____

Answer: regression

Biostatistics Flashcard 2 of 5

Question: _____ distribution is the probability distribution that describes the chances of an event in a particular time frame

Answer: Poissons

Biostatistics Flashcard 3 of 5

Question: Values such as rank orders, or mild-moderate-severe represent _____ scale data

Answer: ordinal

Biostatistics Flashcard 4 of 5

Question: _____ refers to the time when 50% of the population is alive

Answer: Median survival

Biostatistics Flashcard 5 of 5

Question: The confidence interval is smaller with a _____ sample size.

Answer: larger (larger/smaller)