In the text book "New Comprehensive Mathematics for O Level" by Greer (1983), I see averaged deviation calculated like this:
Sum up absolute differences between single values and the mean. Then get its average. Througout the chapter the term mean deviation is used.
But I've recently seen several references that use the term standard deviation and this is what they do:
Calculate squares of differences between single values and the mean. Then get their average and finally the root of the answer.
I tried both methods on a common set of data and their answers differ. I'm not a statistician. I got confused while trying to teach deviation to my kids.
So in short, are the terms standard deviation and mean deviation the same or is my old text book wrong?