University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

262

Pages:

2
Author:

Mariam A. A.

Measuring association – relative risk of a disease occurrence rate Effect magnitude • Clinical studies aim to generate new knowledge of effectiveness of healthcare interventions • Involves estimating key parameter of interest (the effect size) (usually a quantitative comparison) • Relative measures tend to emphasise potential benefits related to the intervention • Absolute measures (Risk difference) provide an across the board summary of benefits accrued to patients • Findings from the study provide a point estimate of this effect Measures of association • How big, or how strong is the association between the study factor (exposure) and the outcome factor (disease)? o Relative Risk o Absolute Risk/Risk Difference o Odds Ratio o Attributable Fraction/Population Attributable Fraction Incidence • Cumulative incidence: • Incidence = measure of events (event rate) 🡪 measure of risk Relative risk • Gives information on the relative effect of the exposure on the disease • How many times higher or lower the disease risk is among the exposed as compared to the unexposed • Commonly used in etiologic research as a measure of risk 45 How to interpret relative risk: • RR = 1 o Risk in exposed = risk in non-exposed o No association • RR > 1 o Risk in exposed > risk in non-exposed o Positive association, factor is associated with disease o Larger RR 🡪 stronger association • RR < 1 o Risk in exposed < risk in non-exposed o Negative association, factor is “protective” Risk for whom compared to whom? 46 Absolute vs. relative risk • Relative measures quantify the strength of association; often of interest to epidemiologists who do etiologic research – strength of relationships • Absolute measures then becomes important (assuming causality) to tell us the potential impact the results have on individuals or communities – burden/impact • E.g. “How much of the disease that occurs can be attributed to a certain exposure?” Ratio vs. difference • Absolute measures usually a difference - how much of the outcome is attributable to exposure (useful in assessing clinical health importance) 🡪 burden • Relative measures usually based on a ratio of risks - a measure of strength of association between exposure and outcome (useful in analytical studies) 🡪 strength Absolute risk • Difference between 2 measures of frequency • Compares disease occurrence among exposed with disease occurrence among unexposed by subtracting one from the other • Gives information on the: o Absolute effect of an exposure on disease outcomes o Excess adverse outcome risk, or morbidity (exposed vs. unexposed) o Health impact of an exposure - how much morbidity would be prevented if exposure was removed ▪ Assuming exposure causes the adverse outcome