(8088) NCCMT - URE - Relative Risk it’s easy to calculate and interpret

Introduction to Relative Risk (RR)

• Definition: Relative risk (RR) measures the likelihood of an event occurring in one group compared to another, helping to determine the strength and existence of relationships between interventions or risk factors and outcomes.

• Significance: Indicates whether a relationship exists and how strong the associated risk is (e.g., relationship between smoking and lung cancer).

Key Characteristics of RR

• Calculation Conditions:

  • RR can only be calculated with two potential outcomes for the event (e.g., compliant vs. non-compliant).

  • Requires a study design where one group is exposed to an intervention/risk and another group is not, with both followed over time.

• Contrasting Odds Ratios (OR): In retrospective studies (looking back), odds ratios (OR) are used instead of relative risk (RR).

Calculating and Interpreting RR: Hypothetical Example

• Scenario: 1,000 children taught oral hygiene versus 1,000 not taught.

• Data Breakdown:

  • Educated Group: 25 develop dental caries, 975 do not

  • Non-Educated Group: 50 develop dental caries, 950 do not

Step-by-Step Calculation

• Risk in Educated Group:

  • Formula: Number with event / Total in group = 25 / 1000 = 0.025

• Risk in Non-Educated Group:

  • Formula: Number with event / Total in group = 50 / 1000 = 0.05

• Calculating RR:

  • RR = Risk in Educated / Risk in Non-Educated = 0.025 / 0.05 = 0.5

Interpreting the RR

• Meaning of RR Values:

  • RR of 1: No difference in risk.

  • RR < 1: Lower risk for the first group (positive outcome).

  • RR = 0.5 indicates a 50% reduction in risk.

• Further Interpretation:

  • If RR was 0.25, risk reduced by 75% (1 - 0.25 = 0.75).

  • If RR was 0.10, risk reduced by 90% (1 - 0.10 = 0.90).

Understanding Positive and Negative Outcomes

• RR < 1: Indicates effectiveness in reducing risk (e.g., dental hygiene education).

Community-Based Interventions Example

• Scenario: Evaluating participation in physical activity among adolescents.

• Data Breakdown:

  • Exposed Group: 100 adolescents, 75 participate in daily activity.

  • Non-Exposed Group: 100 adolescents, 45 participate in daily activity.

Step-by-Step Calculation of RR in Physical Activity

• Risk for Exposed Group:

  • 75 / 100 = 0.75

• Risk for Non-Exposed Group:

  • 45 / 100 = 0.45

• Calculating RR:

  • RR = 0.75 / 0.45 = 1.67

Interpreting RR in Physical Activity Intervention

• Meaning of RR:

  • RR greater than 1 indicates higher likelihood of activity participation among exposed.

  • RR of 1.67 means exposed adolescents are 67% more likely (1.67 - 1 = 0.67) to engage in daily activity.

• Importance: Values above 1 indicate the effectiveness of the intervention.

Conclusion

• Importance of Relative Risk in Public Health:

  • RR helps determine the relationship between interventions/risk factors and outcomes.

  • Used alongside other evidence for guiding public health decisions.

  • With practice, calculating and interpreting RRs becomes a powerful tool for informed decision-making.