Biostatistics Practice Questions

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.

Q: Which of the following is a disadvantage of non-randomized trials?

Degree of comparability is low. ***Degree of comparability is low*** - Non-randomized trials have a **lower degree of comparability** between intervention and control groups because subjects are not randomly assigned, making it more difficult to attribute observed differences solely to the intervention. - This lack of comparability increases the risk of **confounding variables** influencing the results, as baseline characteristics of the groups may differ significantly. *Random assignment of subjects* - This is a *feature of randomized controlled trials (RCTs)*, not a disadvantage of non-randomized trials. RCTs use random assignment to create comparable groups. - In non-randomized trials, **random assignment is absent**, which is precisely why comparability can be low. *The experiment can serve as its own control or can utilize a natural control* - This describes a potential **advantage or characteristic of certain non-randomized designs**, like before-and-after studies or natural experiments. - While it can be useful in some contexts, it does not mitigate the fundamental issue of **low comparability** in non-randomized designs when comparing different groups. *Several trials may be needed before evaluation is considered conclusive.* - This statement applies broadly to many types of research, including some randomized trials, and indicates the need for **replication and robust evidence**. - While non-randomized trials might indeed require more supportive evidence due to their inherent limitations, this is a general research principle and not a unique disadvantage stemming from non-randomization itself, compared to the direct impact on comparability.

Q: What is the neonatal mortality rate in a population where there were 4050 total births, 50 stillbirths, and 150 total neonatal deaths within the first 28 days of life (which includes 50 deaths within the first 7 days)?

37.5. ***37.5*** - **Neonatal mortality rate (NMR)** is calculated as deaths occurring within the first **28 completed days of life** per 1000 live births. - **Calculation**: Live births = 4050 total births - 50 stillbirths = 4000; NMR = (150 total neonatal deaths / 4000 live births) × 1000 = **37.5 per 1000 live births**. *30.0* - This incorrect value represents a **miscalculation** that doesn't correspond to any logical subset of the given data in the question. - **Error**: Even using only early neonatal deaths (50 deaths in first 7 days) would yield (50/4000) × 1000 = **12.5**, not 30.0, indicating a fundamental computational error. *45.0* - This value incorrectly includes **stillbirths** in the numerator or uses wrong denominators in the calculation. - **Error**: Stillbirths are **not counted** in neonatal mortality; only deaths after live birth are included in NMR calculations. *25.0* - This represents a significant **undercounting** of neonatal deaths, possibly using only partial death data. - **Error**: Fails to account for the complete **150 neonatal deaths** within 28 days, leading to substantial underestimation.

Q: In a cohort study conducted with 100 individuals in each group (exposed and non-exposed), out of those exposed to the risk factor, 10 are diseased, and out of those not exposed to the risk factor, only 5 are diseased. What is the relative risk?

2. ***Correct Option: 2*** - The **incidence in the exposed group** is 10/100 = 0.1. - The **incidence in the non-exposed group** is 5/100 = 0.05. - **Relative risk (RR)** is calculated as the ratio of the incidence in the exposed group to the incidence in the non-exposed group: 0.1 / 0.05 = 2. - This indicates that the **exposed group has twice the risk** of developing the disease compared to the non-exposed group. *Incorrect Option: 1.5* - This value would be obtained if the ratio of incidences was 0.075 / 0.05 or 0.1/0.066, which is not consistent with the given data. - An RR of 1.5 indicates a **lesser strength of association** than what is observed in this study. *Incorrect Option: 0.75* - This value would result if the incidence in the exposed group was *lower* than in the non-exposed group (e.g., 0.05 / 0.066), suggesting a **protective effect**. - An RR < 1 implies that exposure is protective rather than a risk factor, which contradicts the given data. *Incorrect Option: 1* - A **relative risk of 1** indicates there is no difference in the risk of disease between the exposed and non-exposed groups. - This would mean the incidence rate in both groups is identical (e.g., 0.1 / 0.1 = 1), which contradicts the provided data where exposed group has higher incidence.

Q: Which of the following is a non-probability sampling method?

Quota sampling. ***Quota sampling*** - In **quota sampling**, researchers select participants based on specific characteristics (e.g., age, gender, ethnicity) to ensure the sample reflects the population proportions of these characteristics. - This method is **non-probability** because the selection of individuals within each quota is not random, and not every member of the population has an equal chance of being selected. *Simple random sampling* - **Simple random sampling** is a **probability sampling method** where every member of the population has an equal and independent chance of being selected. - This is typically achieved through random number generators or drawing names from a hat. *Systematic random sampling* - **Systematic random sampling** is a **probability sampling method** where sample members are selected at regular intervals from a list of the population. - The starting point is chosen randomly, but subsequent selections follow a predetermined pattern, ensuring a systematic, yet random, selection. *Cluster sampling* - **Cluster sampling** is a **probability sampling method** where the population is divided into naturally occurring groups (clusters), and then a random sample of these clusters is chosen. - Once clusters are selected, all individuals within the chosen clusters, or a random sample of individuals from them, are included in the study.

Q: APGAR scores of 30 children are recorded in a hospital, and most of the readings are found to be 7 or above. What can be inferred about this data distribution?

Negatively skewed data. ***Negatively skewed data*** - A distribution is **negatively skewed** when the bulk of the data is concentrated at the **higher end** of the scale - In this case, most **APGAR scores are 7 or above** (out of maximum 10), indicating a **left-skewed or negatively skewed distribution** - The tail of the distribution extends toward the **lower values**, while the peak is at the **higher end** - In negatively skewed data: **Mean < Median < Mode** *Positively skewed data* - **Positively skewed data** would imply that most APGAR scores were at the **lower end** of the scale, with a tail extending toward higher values - This is contrary to the observation that most scores are 7 or above - In positively skewed data: **Mode < Median < Mean** *Normal distribution* - A **normal distribution** implies a **symmetrical bell-shaped curve** where data is evenly distributed around the mean - The description "most readings are 7 or above" clearly indicates an **asymmetrical distribution**, not a normal one - In normal distribution: **Mean = Median = Mode** *Symmetrical data* - **Symmetrical data** means the distribution is balanced, with equal spread on both sides of the center - The given condition that most readings are at the **higher end (7 or above)** signifies an **imbalance**, ruling out symmetry

Question 1

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 2

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 3

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 4

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

Question 5

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 6

Which of the following is a disadvantage of non-randomized trials?

Accepted Answer

Degree of comparability is low

Answer

Random assignment of subjects

Answer

The experiment can serve as its own control or can utilize a natural control

Answer

Several trials may be needed before evaluation is considered conclusive.

Question 7

What is the neonatal mortality rate in a population where there were 4050 total births, 50 stillbirths, and 150 total neonatal deaths within the first 28 days of life (which includes 50 deaths within the first 7 days)?

Accepted Answer

37.5

Answer

30.0

Answer

45.0

Answer

25.0

Question 8

In a cohort study conducted with 100 individuals in each group (exposed and non-exposed), out of those exposed to the risk factor, 10 are diseased, and out of those not exposed to the risk factor, only 5 are diseased. What is the relative risk?

Accepted Answer

2

Answer

1.5

Answer

0.75

Answer

1

Question 9

Which of the following is a non-probability sampling method?

Accepted Answer

Quota sampling

Answer

Simple random sampling

Answer

Systematic random sampling

Answer

Cluster sampling

Question 10

APGAR scores of 30 children are recorded in a hospital, and most of the readings are found to be 7 or above. What can be inferred about this data distribution?

Accepted Answer

Negatively skewed data

Answer

Positively skewed data

Answer

Normal distribution

Answer

Symmetrical data

Biostatistics — MCQs

Biostatistics — MCQs

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