Thus, the intervention reduced the odds of death by 12%, or the intervention reduced the odds of death by 88% of what they were in the control group (The Cochrane Collaboration, 2010). If the number of events in the treatment or intervention group is 15 per 100 intervention group members, the odds are 15 to 85. receiving placebo) is 60 per 100 control group members, the odds are 60 to 40 (i.e. For example, if the number of events (e.g. Odds Ratio, commonly abbreviated to OR, is calculated by dividing the odds of an event occurring in the intervention group by the odds of that event occurring in the control group or the odds that a patient was exposed to a given risk factor divided by the odds that a control patient was exposed to the risk factor (BMJ Publishing Group Ltd., & RCN Publishing Company Ltd., 2009 Moher, Jadad, & Klassen, 1998). A p-value of 0.6, for example, means that there is a 60% probability that any deviation is due to chance only.| accept the null hypothesis) (Higgins et al., 2003). |A p-value 0.05 (or sometimes > 0.10) means there is no heterogeneity and chance alone accounts for differences between studies (i.e. begins to detect heterogeneity that is clinically unimportant) when there are many studies (Higgins & Green, 2009).
cannot detect heterogeneity that is clinically important) when there are only a few studies and excessive power (i.e. Cochran’s Q is not considered the most effective test of heterogeneity. Afterwards, a p-value is calculated (see p-value). It is calculated as the weighted sum of squared differences between individual study effects and the pooled effect across studies. The confidence interval defines the range where it's most likely to be.|Ĭochran’s Q, distributed as a chi-square (X 2) statistic, examines the null hypothesis that all studies of a review are examining the same effect in other words, whether observed differences in results are the result of chance alone (Higgins & Green, 2009 Higgins, Thompson, Deeks, & Altman, 2003). death), with a given intervention, to a 26% increase in events (Davies & Crombie, 2009). Therefore, the observed difference is not statistically significant the true value could be anything from a 15% reduction in events (e.g. The CI captures the value of 'no effect' (i.e. Take, for example, a relative risk reported as 1.03 with a CI (0.85 - 1.26). the null effect: 1 for odds and risk ratios, or 0 for mean differences) (DiCenso, 2001). The results of a study are statistically significant when its confidence interval does not include the value corresponding to no difference between values of interest (e.g.
estimate of true value see point estimate) is less precise. A wider CI means the sample is more variable and the point estimate (i.e.
The CI is usually reported as '95% CI', which means that 95% of the time the true value for the population lies within the given range of values (BMJ Publishing Group Ltd. the effect of an intervention or treatment). CI, the common abbreviation of confidence interval, provides the likely range of the true value of interest (e.g.
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