query re normalising data for an unpaired (indep. samples) t-test Watch

purplefrog
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Hi,

this probably could be a sixth form level question but unsure...

I have a some data for a variable I'd like to compare. Prior to running the t-test in SPSS, I split the variable so I could see histograms of the variable in each category.

To keep it simple, let's say I'm comparing height in boys and girls. I split height by boys and girls to gain a histogram for each. The histogram for boys is pretty much normally distributed whereas the histogram for girls is negatively skewed.

I take it when normalising data (in this case I'd be doing an x^2, x^3 or e^x transformation to try and normalise a negative skew) I would need to apply the same transformation across the entire variable not to just the boys/girls? Or is it possible to normalise only one part of the data?

If do this and it as results in the other sex's distribution being skewed, would it mean I can't I do a t-test and should do a Mann-Whitney U test instead?




Also on a separate note: I've collected data where I've picked up measurements over time. I've then taken the median and inter-quartile range. When comparing the inter-quartile range values (these are my summary values for the dataset) between the sexes, would I carry out a Mann Whitney U test by default seeing as the data they originated from are not normally distributed? Or would I check (and try to correct for) a normal distribution for the range of IQR values and perform an unpaired t-test?
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