Relative risk reduction , calculation

Calculating the effect size of a therapeutic intervention is central (step 3 in Box 3.3). Different ways to calculate effects sizes can be applied as described in Table 3.2. All statements in this box actually describe the effect sizes correctly. Is the efficacy higher for drug A than for drug B Probably not since the relative risk reduction is not identical. Instead the result probably reflects other differences such as higher morbidity (blood pressure, other risk factors, or diseases) in case A. 

Recent publications on major clinical trials whose implications will involve a recommendation to change clinical practice have included summary statistics that quantify the risk of benefit or harm that may occur if the results of a given trial are strictly applied to an individual patient or to a representative cohort. Four simple calculations will enable the non-statistician to answer the simple question How much better would my chances be (in terms of a particular outcome) if I took this new medicine, than if I did not take it . These calculations are the relative risk reduction, the absolute risk reduction, the number needed to treat, and the odds ratio (see Box 6.3). 

The estimated risk of dying in the first 12 months is then 0.114 in the cavedilol group compared to 0.185 in the placebo group. This enables the calculation of a relative risk at 12 months as 0.114/0.185 = 0.62 and the relative risk reduction is 38 per cent. Similar calculations can be undertaken at other time points. 

When the relative risk is less than one, as in this case, we often also calculate the reduction in the relative risk ... 

A variety of factors and methods were used to evaluate and rank the twelve options. For example, the study team considered the reduction in relative risk to human health achieved by different options. Generally, an option s effectiveness in reducing health risks was evaluated by calculating its effect on exposure to benzene emissions. The study team selected benzene emissions as an indicator because benzene can be found in all waste media (air, water, groundwater, and surface water) and poses a known threat to human health. 

While the relative risk is a standard statistic that can be used to compare treatments, it can be difficult to understand and to relate to practice. For example, although the relative risk of 3.7 that was calculated above indicates that Drug A is associated with nearly four times the risk of cure compared with Drug B, this gives no indication of the practical implications. For this reason, effects are often quoted as the Number Needed to Treat (NNT). The NNT is calculated as the reciprocal of the absolute risk reduction (ARR). In the example in Table 3, the NNT refers to the number of patients who need to receive Drug A before an additional cure is likely to occur. 

The results of the PFDavg calculations for SIL 3 Case 2 indicate that for a one-year test interval the PFDavg is 7.01E-03. This provides a Risk Reduction of 143 (S1L2). The relative subsystem contribution is shown in Figure 12-10. This clearly shows that the final element design must be improved to achieve a SIL 3 rating for the safety instrumented function. The three-year proof test interval was not calculated. 

By making assumptions about the numerical value of the above scores, it is possible to construct a spreadsheet that calculates a global risk score for both the baseline and ATM versions of the motorway. This spreadsheet can also be used to test the sensitivity to other uncertainties, e.g. the effect of changing the scores for individual hazards, the effect of assumptions made about the relative value of event and state hazards, or the effect of risk reduction effort on the large scoring hazards. 

Therefore %reduction in RPN = 100 (336 — 140)/336 = 58.3%. From here it can be concluded that RPN is a method to assess the relative risk for a particular analysis and is a helpful tool. Also there can be several revised methods or techniques to calculate this and apply it for the analysis best suited. Another... 

The calculation of hazard quotients (HQs) was a useful tool to estimate the hazards that the occurrence of PhACs may pose to aquatic organisms. It was estimated that the overall relative order of susceptibility was algae>daphnia>fish. Results indicated that the reduction of pharmaceuticals concentration after wastewater treatment, as well as the dilution factor once they are discharged into the receiving river waters, efficiently mitigates possible environmental hazards. Nevertheless, risks are expected to be higher in areas with low river flow. 

---