Are the results of this study important?
How likely are the outcomes over time?
Typically, results of prognosis studies are reported in one of three ways: as a percentage of the outcome of interest at a particular point in time (e.g. 1 year survival rates), as median time to the outcome (e.g. the length of follow-up by which 50% of patients have died) or as event curves (e.g. survival curves) that illustrate, at each point in time, the proportion of the original study sample who have not yet had a specified outcome.
From the study we found, the risk of seizure after any type of stroke is 5.7% at 1 year.
How precise is this prognostic estimate?
The precision of the estimate is best reflected by its 95% confidence interval; the range of values within which we can be 95% sure that the population value lies. The narrower the confidence interval, the more precise is the estimate. If survival over time is the outcome of interest, earlier follow-up periods usually include results from more patients than later periods, so that survival curves are more precise (i.e. have narrower confidence intervals) earlier in follow-up.
To calculate the 95% confidence interval for the study we identified, we can use the following equation:
95% Confidence Interval = p +/- 1.96 x SE
Standard Error (SE) =
And 'p' is a proportion of people with the outcome of interest and 'n' is the sample size.
From the study, n = 675 and p = 0.057
SE = 0.009
Therefore the 95% CI is:
0.057 +/- 1.96 x 0.009 = 3.9% to 7.5%