Biostatistics Practice Questions

Q: The ability of a screening test to detect true positives is known as:

Sensitivity. ***Sensitivity*** - **Sensitivity** refers to the ability of a screening test to correctly identify individuals who truly **have a disease** (true positives). - A highly sensitive test will have a low rate of **false negatives**. - **Clinical application (SnNout)**: When a highly **sensitive** test is **negative**, it helps rule **out** the disease. *Specificity* - **Specificity** is the ability of a test to correctly identify individuals who do **not have the disease** (true negatives). - A highly specific test has a low rate of **false positives**. - **Clinical application (SpPin)**: When a highly **specific** test is **positive**, it helps rule **in** the disease. *Positive predictive value* - **Positive predictive value (PPV)** is the probability that an individual with a **positive test result** actually has the disease. - PPV is influenced by the **prevalence of the disease** in the population being tested. *Negative predictive value* - **Negative predictive value (NPV)** is the probability that an individual with a **negative test result** actually does not have the disease. - NPV is also affected by the **prevalence of the disease**; a lower prevalence generally leads to a higher NPV.

Q: What is the probability of selecting a patient who requires surgery from a total of 50 admissions, where 10 girls and 20 boys needed surgery?

3/5. ***3/5*** - The total number of patients requiring surgery is the sum of girls and boys who needed surgery: **10 (girls) + 20 (boys) = 30 patients**. - The probability is calculated by dividing the number of favorable outcomes (patients needing surgery) by the total number of possible outcomes (total admissions): **30 / 50 = 3/5**. *3/10* - This option would be correct if only 15 patients (e.g., 5 girls and 10 boys) needed surgery out of 50 admissions. - It incorrectly calculates the proportion of patients requiring surgery relative to the total admissions. *1/2* - This option would imply that **25 out of 50** patients required surgery, which contradicts the given numbers. - It represents a **50% probability**, which is not supported by the calculation of 30 patients out of 50. *1/3* - This option would be correct if approximately **17 out of 50** patients needed surgery (16.67 rounded), which is not the case here. - It misrepresents the ratio of patients needing surgery to the total admissions, as **30/50 simplifies to 3/5, not 1/3**.

Q: A study is to be conducted to compare the fat content in the expressed breast milk of pre-term infants with that of term infants. Which study design is best suited?

Prospective cohort. ***Prospective cohort*** - Among the given options, a **prospective cohort study** is the most appropriate design for this comparative study. - The study involves identifying two groups (mothers of pre-term vs. term infants) and **prospectively collecting breast milk samples** to measure and compare fat content between these groups. - This design allows for **standardized data collection** moving forward in time, ensuring consistent measurement protocols for both groups. - While this is essentially a comparative cross-sectional measurement, the prospective nature ensures proper sample collection and reduces recall bias. *Case control* - This design is used to compare **exposures** between those with and without an outcome (typically a disease). - Fat content in breast milk is a **continuous biological variable**, not a disease outcome, making case-control design inappropriate. - Case-control studies work backward from outcome to exposure, which doesn't fit this scenario where we're comparing groups defined by infant term status. *Longitudinal study* - While **prospective cohort** is a type of longitudinal study, this term is too broad and non-specific. - Longitudinal studies involve repeated measurements over time, but this question asks for a specific study design for comparing two groups. - Simply stating "longitudinal study" doesn't specify the comparative framework needed. *Ambispective* - An **ambispective (or ambi-directional) study** combines retrospective and prospective components, using existing historical data plus new follow-up. - This design is unnecessary here as there's no indication of existing historical data to utilize. - The study can be conducted entirely prospectively by identifying mothers and collecting fresh breast milk samples for analysis.

Q: What is the probability that a value chosen from a community will be above the median?

0.5. ***0.5*** - The **median** is defined as the value that divides a dataset into two equal halves. - This means that **50% of the values** in the dataset are below the median, and **50% are above** the median. *0.25* - This would imply that only 25% of the data lies above the median, which contradicts its definition as the midpoint. - The value 0.25 is typically associated with **quartiles**, not the median. *0.6* - This indicates that 60% of the values are above the median, which is inconsistent with the median's role in splitting data evenly. - Such a probability would suggest that the chosen value falls into the **upper 60% segment**, not simply above the median. *1* - A probability of 1 means that it is **certain** for a value to be above the median, which is incorrect. - This would only be true if all observed values were greater than the median, which is not possible as the median itself is a data point or derived from data points.

Q: What is the shape of a normal distribution curve?

Bell-shaped. ***Bell-shaped*** - A **normal distribution** is a **symmetric probability distribution** centered around its mean, with tails that taper off indefinitely. - The distinctive shape resembles a **bell**, with the highest point at the mean and gradually decreasing frequencies as values move away from the mean. *J-shaped* - A **J-shaped curve** typically describes a distribution where the frequency is highest at one end and then continuously decreases or increases to the other end. - This shape is not characteristic of the **symmetry** and **central tendency** observed in a normal distribution. *U-shaped* - A **U-shaped curve** indicates that frequencies are highest at both ends of the distribution and lowest in the middle. - This is the opposite of a **normal distribution**, where the highest frequency is at the center (mean). *None of the options* - The term **bell-shaped** accurately describes a normal distribution curve, making this option incorrect.

Q: In a clinical study evaluating a new diagnostic test for a disease, the test was found to have 60 true positives out of 100 positive results. What is the positive predictive value of the test?

60/100. ***60/100*** - The **positive predictive value (PPV)** is the proportion of **true positives** among all positive test results. - Given 60 true positives out of 100 positive results, the calculation is 60 divided by 100. *40/100* - This value would represent the number of **false positives** (positive test results that are actually negative) out of all positive test results, which is not the positive predictive value. - The PPV is specifically concerned with the reliability of a positive result indicating the presence of the disease. *40/300* - This fraction does not correspond to a standard measure of diagnostic test validity given the provided information regarding true positives and total positive results. - It might incorrectly combine disparate data points or represent a miscalculation based on other variables not supplied. *240/300* - This value is not derived from the provided numbers for true positives and total positive results in the context of positive predictive value. - It could potentially represent sensitivity or specificity calculations, but it is not the **positive predictive value**.

Q: Which of the following is not a characteristic of a systematic review?

Meta analysis is always performed. ***Meta-analysis is always performed*** - While **meta-analysis** is frequently a component of a systematic review, it is not always performed; it is only feasible when the included studies are sufficiently homogeneous and quantitative synthesis is appropriate. - A systematic review can identify, appraise, and synthesize evidence without statistically combining results, especially when studies are too **heterogeneous**. *Search for literature is compulsory using explicit search strategy* - A **comprehensive and explicit search strategy** is a defining characteristic of a systematic review, ensuring all relevant literature is included and bias is minimized. - This systematic approach helps to identify all studies on a given topic, regardless of their outcome. *Research questions always focused* - Systematic reviews are driven by **clearly defined and focused research questions** (often in PICO format: Population, Intervention, Comparison, Outcome) to guide the search, selection, and analysis processes. - A focused question ensures the review has a narrow scope, allowing for a thorough and relevant synthesis of the evidence. *Critical appraisal is always criteria-based* - **Critical appraisal** using predefined criteria (e.g., risk of bias tools) is a mandatory step in a systematic review to evaluate the methodological quality and validity of the included studies. - This systematic assessment helps to determine the strength of the evidence and its applicability.

Question 1

The ability of a screening test to detect true positives is known as:

Accepted Answer

Sensitivity

Answer

Specificity

Answer

Positive predictive value

Answer

Negative predictive value

Question 2

What is the probability of selecting a patient who requires surgery from a total of 50 admissions, where 10 girls and 20 boys needed surgery?

Accepted Answer

3/5

Answer

3/10

Answer

1/2

Answer

1/3

Question 3

In the context of medical screening, how does a series testing approach affect the net sensitivity and net specificity of the screening methods?

Accepted Answer

Net sensitivity is decreased and net specificity is increased

Answer

Net sensitivity and net specificity are both increased

Answer

Net sensitivity is increased and net specificity is decreased

Answer

Net sensitivity remains the same and net specificity is increased

Question 4

A study is to be conducted to compare the fat content in the expressed breast milk of pre-term infants with that of term infants. Which study design is best suited?

Accepted Answer

Prospective cohort

Answer

Longitudinal study

Answer

Ambispective

Answer

Case control

Question 5

What does the term 'validity' mean in the context of indicators?

Accepted Answer

It accurately measures the concept it is intended to assess.

Answer

Indicators should reflect changes in the situation being evaluated.

Answer

Indicators must be capable of collecting relevant data.

Answer

The measurement should yield consistent results across different evaluators under similar conditions.

Question 6

What is the probability that a value chosen from a community will be above the median?

Accepted Answer

0.5

Answer

1

Answer

0.25

Answer

0.6

Question 7

What is the shape of a normal distribution curve?

Accepted Answer

Bell-shaped

Answer

J-shaped

Answer

U-shaped

Answer

None of the options

Question 8

In a clinical study evaluating a new diagnostic test for a disease, the test was found to have 60 true positives out of 100 positive results. What is the positive predictive value of the test?

Accepted Answer

60/100

Answer

40/100

Answer

40/300

Answer

240/300

Question 9

Which of the following statements accurately describes a characteristic of a random sample?

Accepted Answer

Any member of a group to be studied has an equal chance of being included in the study.

Answer

Every nth name on a list is selected in a systematic manner.

Answer

Subjects in the study are volunteers who choose to participate.

Answer

A person in a control group cannot be a member of the experimental group.

Question 10

Which of the following is not a characteristic of a systematic review?

Accepted Answer

Meta analysis is always performed

Answer

Search for literature is compulsory using explicit search strategy

Answer

Critical appraisal is always criteria based

Answer

Research questions always focused

Biostatistics — MCQs

Biostatistics — MCQs

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