Dear Everyone,
1. How to convert GDS , BDI 11, ADI -2 , PHQ-9 raw -score to Z score ? so that i can have standardized score to calculate the mood disorder in my study ?
- Could you share links for any study that can be used for conversions of those Raw Score for those assessments to standardized Z score ?
- Thank You Very Much
"The formula for converting a raw score into a z-score is Z = (M – X) / SD, or Z Score = (Mean – Value) / Standard Deviation. So, if you have a score of 80, and the mean is 75, with a Standard Deviation of 5, your equation will be: (80 – 75) / 5 = 1."
Z-Scores - Dustin K MacDonald
dustinkmacdonald.com/z-scores/
There are also internet calculators that do this for you: Z-score Calculator
https://calculator.net/z-score-calculator
z-scores are misleading when the data are skewed, which these measures all are. The skewness and outlying scores affect the standard deviation more than the mean, because of the effect of squaring the distance between the mean and the value. This in turn affects the z-score.
Finally, but importantly, these scores a) do not have a defined unit and b) are on a bounded scale, which also make their distributions depart from a normal distribution in pretty definitive ways.
So while the arithmetic is simple, as Béatrice has already pointed out, and can be applied to all the scales, there are no grounds for believing that the resulting z-score represents a monotonic transformation of the values – the transformation will not be symmetric about the mean – or that it will affect all scales equally – the transformation will distort the values in a way unique to each scale.
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