From the Guidelines
A relative risk of 1.33 means that the risk of an outcome in one group is 33% higher than the risk in the comparison group. This is a measure of the strength of association between an exposure and an outcome, and it can be useful for comparing the risks of different exposures. For example, if a study found that a certain exposure had a relative risk of 1.33 compared to a control group, this would mean that the exposed group is 1.33 times more likely to experience the outcome than the control group, or their risk is 33% higher 1.
When interpreting a relative risk of 1.33, it's essential to consider the baseline risk of the outcome, as even a 33% increase might represent a small absolute difference in risk if the baseline risk is very small. Relative risk values above 1 indicate increased risk, while values below 1 indicate decreased risk, and a value of exactly 1 means there is no difference in risk between the groups.
Some key points to consider when interpreting relative risk include:
- The size of the relative risk: a larger relative risk indicates a stronger association between the exposure and the outcome
- The baseline risk: if the baseline risk is very small, even a large relative risk might represent a small absolute difference in risk
- The confidence interval: if the confidence interval for the relative risk includes 1, it suggests that the association between the exposure and the outcome may be due to chance
- The study design and population: relative risks can vary depending on the study design and population being studied, so it's essential to consider these factors when interpreting the results.
In the context of the provided evidence, the relative risks of gastrointestinal illness associated with different levels of exposure to indicators of water quality are presented in a table, with relative risks ranging from 1.15 to 3.86 1. The relative risk of 1.33 should be considered in the context of the specific exposure and outcome being studied, and it's crucial to evaluate the strength of the evidence and the potential for bias and confounding when interpreting the results.
From the Research
Understanding Relative Risk
- A relative risk of 1.33 means that the risk of an event occurring in the exposed group is 1.33 times higher than in the non-exposed group 2.
- In other words, for every 100 people in the non-exposed group, 133 people in the exposed group would experience the event.
- Relative risk is often used to express the strength of association between a risk factor and an outcome, but it can be misleading if not interpreted in the context of the absolute risk 3.
Interpreting Relative Risk
- A relative risk of 1.33 can be considered moderate, but its significance depends on the underlying absolute risk of the event 2.
- For example, if the absolute risk of an event is very low, a relative risk of 1.33 may not translate to a significant increase in absolute risk.
- It is essential to consider both relative and absolute risk measures when interpreting the results of epidemiological studies 2.
Limitations of Relative Risk
- Relative risk can be sensitive to the baseline risk of the event, and its interpretation may vary depending on the population being studied 3.
- The use of relative risk as the sole measure of association can be misleading, and it is recommended to report both relative and absolute risk measures 2.
- The choice of effect measure, including relative risk, odds ratio, or risk difference, depends on the research question and the study design 3.