Confidence levels can give us information that confidence intervals cannot. For example, we can calculate the level of confidence that a survival benefit exists with immediate nodal dissection, as follows.

We need to determine how much confidence lies below 1.00 (HR < 1.00 indicates a survival benefit). From the WHO study, the point estimate hazard ratio for survival was 0.72, with a standard error of 0.192 (extrapolated from the original publication).

• 1. Calculate the confidence interval around the hazard ratio with an upper limit of 1.00 (93% CI in this example)

• 2. Calculate how much confidence lies below this confidence interval (half of 7% = 3.5%)

• 3. Add the two percentages (93 + 3.5 = 96.5%)

Thus there is 96.5% confidence that a survival benefit exists.

This is very high despite the lack of significance!