Question 247:

Asked on June 24, 2008

Tags: Confidence Intervals , Adjusted Wald , Z-Score

1

Answer:

No answer provided yet.

Sure, the adjusted wald calculatoions are examplained on the confidence interval around a proportion page:

It adds half of the squared Z-critical value to the numerator and the entire squared critical value to the denominator before computing the interval i.e (x+z²/2)/(n+z²). For example, a 95% confidence level uses the Z-critical value of 1.96 or approximately 2. If you observe 9 out of 10 users completing a task, this formula computes the proportion as( 9 + (1.96²/2) )/ (10 + (1.96²)) = approx. 11/14 and builds the interval using the Wald formula.

The calculations just use the z-score for 95% to more decimal-points than 1.96, which you can look-up using the percentile to z-score calculator and entering .95.