Confidence intervals are calculated by:
Upper = mean + (1.96 x SE)
Lower = mean - (1.96 x SE)
Therefore, you can get:
Upper – Lower = mean – mean + (1.96 x SE) + (1.96 x SE)
The means just cancel out and you end up with
Upper – Lower = 3.92 x SE
Upper – Lower/ 3.92 = SE
So to calculate SE from an upper and lower confidence interval all you do is this,
Upper = mean + (1.96 x SE)
Lower = mean - (1.96 x SE)
Therefore, you can get:
Upper – Lower = mean – mean + (1.96 x SE) + (1.96 x SE)
The means just cancel out and you end up with
Upper – Lower = 3.92 x SE
Upper – Lower/ 3.92 = SE
So to calculate SE from an upper and lower confidence interval all you do is this,