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Biostatistics @Measures of Central Tendency

Biostatistics – PSM Quick Revision Notes 1. Types of Data • Qualitative: Nominal (gender, blood group), Ordinal (stage, grade) • Quantitative: Discrete (number of children), Continuous (height, weight) 2. Measures of Central Tendency • Mean = Sum of observations / Number of observations • Median = Middle value after arranging in order • Mode = Most frequent value • Mean affected by extreme values; Median not affected. 3. Measures of Dispersion • Range = Max – Min • Variance = Average of squared deviation from mean • Standard Deviation (SD) = √Variance • Coefficient of Variation (CV) = SD/Mean × 100 4. Normal Distribution • Bell-shaped symmetric curve • Mean = Median = Mode • 68% within ±1 SD • 95% within ±2 SD • 99.7% within ±3 SD 5. Sampling Methods • Random sampling – each individual equal chance • Systematic sampling – every nth individual • Stratified sampling – population divided into strata • Cluster sampling – groups selected instead of individuals 6. Types of Study Designs • Descriptive: Case report, case series, cross-sectional • Analytical: Case-control, cohort • Experimental: Randomized controlled trial (RCT) 7. Hypothesis Testing • Null hypothesis (H0): No difference/association • Alternative hypothesis (H1): Difference exists • p-value 0.05 → statistically significant • Type I error (α): Rejecting true H0 • Type II error (β): Accepting false H0 8. Tests of Significance • Chi-square test – qualitative data • Student t-test – compare two means • ANOVA – compare more than two means • Correlation (r): strength of relationship • Regression: prediction equation 9. Epidemiological Indicators • Incidence = New cases / Population at risk • Prevalence = All cases / Population • Sensitivity = TP/(TP+FN) • Specificity = TN/(TN+FP) • PPV and NPV depend on prevalence 10. Common Exam Pearls (NEET PG/INI-CET) • Median preferred for skewed data • Mode used for categorical data • Case-control → Odds Ratio • Cohort → Relative Risk • RCT gives strongest evidence