ANOVA, including Welch's is out of the question. Is Kruskal-Wallis the only option? Any other tests/options i haven't considered?

Cheers.

- Thread starter Prometheus
- Start date
- Tags skewed distribution

ANOVA, including Welch's is out of the question. Is Kruskal-Wallis the only option? Any other tests/options i haven't considered?

Cheers.

The data is from a Raman spectroscopy dataset. Basically we get a spectral graph like that in attachment 'RawSpectra_Baseline'. Most of this spectra is due to fluorescence instead of Raman scattering and the red curve is an estimation of this fluorescence.

There are nearly two thousand such spectra, obtained from biological samples with 4 different types of fixation method. We are investigating whether the different fixation methods have a difference on estimated fluorescence, which we are measuring as the area under the estimated curve.

It is these areas which are unbalanced and heteroscedastic. The histograms are in the attachment 'Fixation_Hists'.

I'm doing this in Matlab and can give that data if people are interested. Cheers.

But there seems to be a lot of data so that a t-test (on transformed scale) could work well.

Om the histogram it looks as if there is an extra "hump" (a bimodal density) for larger values in the first two diagram. Maybe the curve-making and area computation just did not work on these data points - so that they are "wrong" and needs to be redone.

Why not attach the data in a text-file or something?

Attached the data. There are two columns, the first is the area under the estimated curves and the second is the group to which the row belongs (1-4), no headers.

Cheers.