Talk:Kuder–Richardson formulas

Formula Explanation
Yet another article giving a formula without explaining all the variables. Pi and Qi would seem to be the proportion of people getting an item correct or incorrect as described here []. It might also be helpful to indicate the variance and associated sum of squares are applied to raw scores with N being the number of people in the sample (not number of test items). —Preceding unsigned comment added by 98.231.152.208 (talk) 15:11, 22 October 2010 (UTC)

Also why the name
Rather unusual name - is there some history behind this? What were KR1 to KR19? — Preceding unsigned comment added by 31.221.13.140 (talk) 09:48, 11 May 2012 (UTC)

What is "Xi"?
This article says The formula for KR-20 for a test with K test items numbered i = 1 to K is


 * $$r= \frac{K}{K-1} \left[ 1 - \frac{\sum_{i=1}^K p_i q_i}{\sigma^2_X} \right] $$

where pi is the proportion of correct responses to test item i, qi is the proportion of incorrect responses to test item i (so that pi + qi = 1), and the variance for the denominator is


 * $$\sigma^2_X = \frac{\sum_{i=1}^n (X_i-\bar{X})^2\,{}}{n}.$$

where n is the total sample size. It never says what $ X_i $ is! Are there people who can read something like that without feeling they're being personally abused? Michael Hardy (talk) 16:03, 8 July 2023 (UTC)