After z-score transform, shape of distribution changes?
Posted: Wed Feb 19, 2020 3:12 am
I was doing a tutorial on jamovi in my undergrad statistics class, and was showing my students how to use the Compute option to create a new variable. I used the Z function to turn an existing variable into a new column of z-scores.
I ran Descriptives on the new z-scores to remind the students that they now had a mean of zero and an SD of one, and as a further demo I requested a histogram to illustrate that the shape of the distribution was unchanged from the original data.
Except... the new histogram HAD changed from the original shape. The original was a normal distribution, but the new histogram of z-scores appeared to be positively skewed. I tried this with other data sets, and got the same result: the histogram of z-scores appeared to be a different shape than for the original data.
i'm not sure if I'm missing something obvious here... Any ideas?
I ran Descriptives on the new z-scores to remind the students that they now had a mean of zero and an SD of one, and as a further demo I requested a histogram to illustrate that the shape of the distribution was unchanged from the original data.
Except... the new histogram HAD changed from the original shape. The original was a normal distribution, but the new histogram of z-scores appeared to be positively skewed. I tried this with other data sets, and got the same result: the histogram of z-scores appeared to be a different shape than for the original data.
i'm not sure if I'm missing something obvious here... Any ideas?