AIIMS PG (DM/MCh) Entrance Community Medicine, Research Methodology and Ethics Syllabus

Define positive predictive value (PPV) and negative predictive value (NPV), and state what they depend on.

PPV = TP/(TP+FP) = probability disease is present given a positive test. NPV = TN/(TN+FN) = probability disease is absent given a negative test. Both depend on disease PREVALENCE (unlike sensitivity/specificity).

How does disease prevalence affect PPV and NPV?

As prevalence rises, PPV increases and NPV decreases. As prevalence falls, PPV decreases (more false positives relative to true) and NPV increases.

Define likelihood ratios: LR positive and LR negative.

LR+ = sensitivity / (1 − specificity); higher values strongly increase post-test probability. LR− = (1 − sensitivity) / specificity; lower values strongly decrease post-test probability. LRs are prevalence-independent.

What does an ROC curve plot, and what does the area under the curve (AUC) indicate?

ROC plots sensitivity (y) against 1 − specificity (x) across cut-offs. AUC measures overall test discrimination: 0.5 = no better than chance, 1.0 = perfect. Higher AUC = better test.

What is the relationship between a test cut-off, sensitivity, and specificity?

Lowering the cut-off (more positives) increases sensitivity but decreases specificity; raising the cut-off increases specificity but decreases sensitivity. There is an inverse trade-off.

Differentiate lead-time bias from length-time bias in screening.

Lead-time bias: apparent survival increases only because diagnosis is earlier, not because death is delayed. Length-time bias: screening preferentially detects slow-growing, less aggressive disease, falsely inflating survival.

What are the Wilson and Jungner criteria themes for a good screening program (name 4)?

The condition is an important health problem; there is a recognizable latent/early stage; a suitable, acceptable, valid test exists; effective accepted treatment is available; facilities for diagnosis/treatment exist; cost is economically balanced; screening is a continuing process.

In critical appraisal, what is intention-to-treat (ITT) analysis and why is it preferred?

ITT analyzes participants in the groups to which they were RANDOMIZED, regardless of adherence or completion. It preserves randomization, avoids attrition/non-compliance bias, and gives a conservative, real-world estimate of effect.

Define Number Needed to Treat (NNT) and how to calculate it.

NNT = number of patients to treat to prevent one additional adverse outcome. NNT = 1 / Absolute Risk Reduction (ARR), where ARR = control event rate − treatment event rate. Lower NNT = more effective.

What is the hierarchy of evidence (strongest to weakest, study designs)?

Systematic reviews/meta-analyses of RCTs > RCTs > cohort studies > case-control studies > cross-sectional studies > case series/case reports > expert opinion.

What is the difference between a systematic review and a meta-analysis?

A systematic review uses explicit, reproducible methods to identify and appraise all relevant studies. A meta-analysis statistically pools quantitative results across studies to produce a combined effect estimate (often part of a systematic review).

In a meta-analysis forest plot, what does the diamond represent and how is heterogeneity quantified?

The diamond represents the pooled (summary) effect estimate and its confidence interval. Heterogeneity is quantified by the I² statistic (and Cochran's Q): I² >50% suggests substantial heterogeneity.

What is the purpose of allocation concealment and blinding in an RCT, and how do they differ?

Allocation concealment hides the upcoming assignment from those enrolling subjects (prevents selection bias at randomization). Blinding hides which intervention a subject received (prevents performance and detection/ascertainment bias during the study).

Describe the four phases of a clinical trial.

Phase I: safety, dosing, pharmacokinetics in small healthy volunteers. Phase II: efficacy and side effects in a small patient group. Phase III: large RCT comparing to standard treatment for efficacy/safety. Phase IV: post-marketing surveillance for long-term/rare effects.

What is a crossover trial and its main limitation?

In a crossover trial each subject receives both treatments sequentially, serving as their own control. Main limitation: carryover effect, requiring a washout period; unsuitable for conditions that change or are cured.

What is equipoise in clinical trials?

Clinical equipoise is genuine uncertainty within the expert community about which treatment arm is superior. It is the ethical precondition that justifies randomizing patients between arms.

What is the role and purpose of a Data and Safety Monitoring Board (DSMB)?

An independent DSMB periodically reviews accumulating trial data for safety and efficacy, and can recommend stopping a trial early for harm, overwhelming benefit, or futility, protecting participant welfare.

What are the key sections of the IMRAD structure for a scientific paper?

IMRAD = Introduction (why), Methods (how), Results (what was found), And Discussion (what it means). Preceded by Title/Abstract and followed by References.

What is the impact factor of a journal and how is it calculated?

Impact factor = number of citations in the current year to articles published in the previous TWO years, divided by the total number of citable articles published in those two years. It estimates a journal's relative influence.

What is publication bias and which plot is used to detect it?

Publication bias is the tendency for positive/significant studies to be published more than negative ones, distorting meta-analyses. A funnel plot is used to detect it; asymmetry suggests bias.

Which reporting guideline applies to RCTs and which to observational studies?

CONSORT for randomized controlled trials; STROBE for observational studies (cohort, case-control, cross-sectional). PRISMA for systematic reviews/meta-analyses.

Which Indian national program targets tuberculosis and what is its current treatment strategy basis?

The National Tuberculosis Elimination Programme (NTEP, formerly RNTCP) targets TB elimination by 2025, based on DOTS/daily fixed-dose regimens, free diagnosis (CBNAAT/NAAT) and treatment, and the Ni-kshay portal.

What is the Universal Immunization Programme (UIP) and name the vaccines given at birth in India.

UIP provides free vaccines against vaccine-preventable diseases. At birth in India: BCG, OPV-0 (zero dose), and Hepatitis B (birth dose).

What are the key thrust areas of the National Health Mission (NHM) in India?

NHM (NRHM + NUHM) focuses on strengthening primary healthcare, maternal and child health (RMNCH+A), ASHA workers, reducing IMR/MMR/TFR, communicable and non-communicable disease control, and universal access in rural and urban areas.

Define Maternal Mortality Ratio (MMR) and Infant Mortality Rate (IMR), including their denominators.

MMR = maternal deaths per 100,000 LIVE BIRTHS. IMR = deaths of infants <1 year per 1,000 LIVE BIRTHS. (Note: MMR denominator is live births, often cited as the key distinction.)

What is the demographic transition theory, and what defines the demographic dividend?

Demographic transition: a population moves from high birth/high death rates to low birth/low death rates through stages, with intermediate population growth. Demographic dividend: economic growth potential from a large working-age population relative to dependents.

Define Total Fertility Rate (TFR) and the TFR value considered the replacement level.

TFR = average number of children a woman would bear in her lifetime at current age-specific fertility rates. Replacement-level fertility ≈ 2.1 children per woman.

Classify protein-energy malnutrition using the Gomez and Waterlow/WHO indicators.

Gomez: based on weight-for-age (% of expected). Waterlow: wasting = low weight-for-height (acute), stunting = low height-for-age (chronic). WHO uses Z-scores; <−2 SD = moderate, <−3 SD = severe.

State the four basic principles of biomedical ethics (Beauchamp and Childress).

Autonomy (respect for self-determination), Beneficence (act in the patient's best interest), Non-maleficence (do no harm), and Justice (fair distribution of benefits, risks, and resources).

What are the essential elements of valid informed consent?

Disclosure of relevant information, comprehension by the participant/patient, voluntariness (no coercion), competence/capacity to decide, and explicit agreement (consent), with the right to withdraw at any time.

What is the difference between confidentiality and the situations permitting its breach, and what is privileged communication?

Confidentiality is the duty to protect patient information. It may be breached when legally mandated or to prevent serious harm to others (e.g., notifiable diseases, court order). Privileged communication is disclosure made in good faith to a lawful authority in the public/third-party interest, protecting the doctor from liability.