4 replies to this topic

[ctfazra]

Quick question, when comparing between 2 groups ---> before and after treatment in test & control groups, I understand that I should use unpaired t-test. In the graph I present the data as log2 ratio to visualize the increase/decrease following treatment. But for statistical analysis, should I use mean of log2 ratio or mean of actual ratios since when I tried both give different p-values? Which one is more appropriate? Thank you.

[hobglobin]

Use your raw data or transformed raw data (if no normal distribution) but not the means.

[ctfazra]

but what if i want to compare the response (ratio) between these 2 groups? Unpaired t-test will compare means (correct me if I'm wrong) so I wonder if it's appropriate to use transformed data (log ratio instead of actual ratio) to get the mean?

[hobglobin]

yes it does, but your post sounded as if you just want to use the means as input for the test.
Anyway the before-after treatments are paired data and I'd test them either separately using raw data with a paired t-test or using ratios with the ratio paired t-test as offered by some software (e.g. graphpad, prism). The normal student's t-test I would not use for ratio data as they're not normal distributed. If not possible to use the ratio test, use the non-parametric alternative the Mann-Whitney U Test...

[ctfazra]

I understand now. Thanks!
btw, sorry for the misunderstanding. non-native speaker's here