DFT-EMREE-BIOSTATISTICS-11-10-2025-MAXEMO

A public health team investigates the burden of obesity among adolescents in a large city. 1,800 students aged 13-18 Y/O are randomly selected from 8 different schools. At a single point in time, investigators measure each student's weight, height, and collect data on age, gender, and family income. The goal is to describe the characteristics of the adolescent population and look for associations between variables. What is the most appropriate classification for this type of study?

• Cohort study

• Case-control study

• Cross-sectional study

• Randomized controlled trial

• Case series

Answer explanation

This study design is a cross-sectional study because it assesses both the outcome (obesity, measured by BMI) and the exposures (age, gender, income) at a single point in time. It provides a "snapshot" of the population and is primarily used to measure prevalence.

A study enrolls 200 T2DM pts with HbA1c >8%. Pts are randomized to receive either a new oral hypoglycemic agent (OHA) or a placebo. The study is double-blinded, and the primary outcome is the change in HbA1c after 6 months. Which of the following best describes this study design?

• Case-control study

• Prospective cohort study

• Randomized controlled trial

• Cross-sectional study

• Case series

Answer explanation

This is a Randomized Controlled Trial (RCT) because it includes the three key elements: an investigator-led intervention (new OHA), a control group (placebo), and randomization of participants. The double-blinding further strengthens this design.

A junior resident is preparing a journal club on the efficacy of a new oral anticoagulant. To form a definitive conclusion, she must base her presentation on the most robust form of medical evidence available. Which study design represents the highest level of evidence?

• Prospective cohort study

• Large randomized controlled trial (RCT)

• Systematic review and meta-analysis

• Case-control study

• Expert opinion

Answer explanation

A meta-analysis sits at the apex of the evidence pyramid. It statistically combines results from multiple high-quality studies (usually RCTs) to provide the most powerful and reliable estimate of an effect.

A public health program aims to ↓ the long-term incidence of COPD and IHD by tracking the prevalence of a key behavior in adults >18 Y/O. If the program's primary metric is the percentage of adults who smoke, how is this indicator best classified?

• Health outcome indicator

• Health systems response indicator

• Process indicator

• Risk factor indicator

• Socioeconomic determinant

Answer explanation

A risk factor indicator measures the prevalence of a behavior (tobacco use) that increases the likelihood of a disease (COPD, IHD). The program seeks to modify this factor to improve future outcomes.

In a study on maternal smoking and childhood asthma, the exposed cohort (children of smokers) undergoes more frequent asthma workups due to higher parental vigilance for respiratory symptoms. This results in a higher reported incidence of asthma in the exposed group. This finding is most likely distorted by which type of bias?

• Recall bias

• Selection bias

• Surveillance bias

• Confounding bias

• Lead-time bias

Answer explanation

Surveillance (Detection) bias occurs when one group is monitored more closely than another, leading to increased case detection. Here, the exposed group's health is scrutinized more, inflating the diagnosis rate.

A new biomarker assay (Sens 99%, Spec 99.5%) for a rare disease (Prevalence 1/50,000) is used for population screening. A 45 Y/O asymptomatic M tests positive. Which performance metric is most substantially decreased when applying this test to a low-prevalence population?

• Specificity

• Sensitivity

• Negative Predictive Value (NPV)

• Positive Predictive Value (PPV)

Answer explanation

PPV is heavily dependent on disease prevalence. In a low-prevalence population, the number of true positives is extremely low compared to the number of false positives, drastically reducing the PPV. This means a positive result is more likely to be false.

A clinical trial compares a novel immunotherapy vs. standard chemo in metastatic NSCLC. The primary outcome is the patient's functional status, measured by the ordinal ECOG performance scale (0-5). What is the most appropriate statistical test to compare the ECOG scores between the two groups?

• Independent samples t-test

• Analysis of variance (ANOVA)

• Chi-square test

• Mann-Whitney U test

• Pearson correlation coefficient

Answer explanation

The Mann-Whitney U test is the correct non-parametric test to compare two independent groups when the outcome variable is ordinal (like the ECOG scale).

A clinical trial on a new drug for liver failure reports 'days to recovery.' The data is right-skewed with the following results: Mean = 18 days, Median = 9 days, Mode = 7 days. You are counseling a patient's family on the expected timeline. Which value is most appropriate to communicate as the typical recovery time?

• Mean (18 days)

• Median (9 days)

• Mode (7 days)

• Range

Answer explanation

In a skewed distribution, the median is the most robust measure of central tendency because it is not affected by extreme outliers. It represents the true middle point of the data, providing a more accurate "typical" value.

A lab compares two cortisol assays. Assay A reports in nmol/L (mean 450, SD 90). Assay B reports in µg/dL (mean 16, SD 4). A clinician needs to compare their relative variability to assess consistency. Most appropriate statistical measure to use?

• Standard deviation (SD)

• Variance

• Coefficient of Variation (CV)

• Standard Error of the Mean (SEM)

Answer explanation

CV (SD/Mean) is a unitless measure of relative variability, essential for comparing datasets with different units or means.

A study measures fasting blood glucose (FBG) in 30 patients with T2DM at baseline and again in the same 30 patients after 8 weeks of a new Rx. The goal is to compare the mean FBG before and after the intervention. Which statistical test is most appropriate for this analysis?

• Chi-square test

• Independent samples t-test

• Paired t-test

• Analysis of Variance (ANOVA)

Answer explanation

The paired t-test is used to compare the means of a single group at two different times (pre- and post-intervention), as the data points are related or "paired."