I have data from an experiment in which five different methods were used to abrade a ceramic and the resulting particle size in the atmosphere measured. Due to the anisotropic nature of the ceramic there is considerable scatter in the data which is right skewed, and robvar shows the data to fail the homogeneity of variance test.
Array
I used a log transform
Array
There is still inhomogeneity in the variance but the distribution of residuals following anova appears to be normal as assessed visually using distplot (from SSC)
. robvar lc, by(method)
| Summary of lc
method | Mean Std. Dev. Freq.
------------+------------------------------------
1 | -4.5900172 .18631618 900
2 | -2.2221745 1.2543433 1,800
3 | -2.2856141 .74755 1,800
4 | -2.6684095 .90676613 900
5 | -3.2487493 .35297332 900
------------+------------------------------------
Total | -2.7889648 1.1870132 6,300
W0 = 572.11260 df(4, 6295) Pr > F = 0
W50 = 528.26727 df(4, 6295) Pr > F = 0
W10 = 552.20502 df(4, 6295) Pr > F = 0
My question is it acceptable to use this log transformed data; or would another transformation be preferable; or should I consider a nonparametric analysis such as dunntest (from SSC).
Thank you.
Eddy
Related Posts with Transform data or use a non-parametric analysis
Find digit(s) in stringI realize that there have been hundreds of questions about extracting digits or numbers from strings…
Motivate (new user submitted command for Stata)Motivate is a new command that was added to SSC Code: ssc install motivate If you become frustra…
weighted kappa 95%CI helpWhen calculating 95%CIs: how do I dictate that my data are 8x8 when some ratings have not been used …
Case-control (4:1 matching)For a case control study, i use CCMATCH to generate a matched control on selected variables. Works p…
using outreg merged table in putpdfI have been using putpdf for generating my report. At one point, I use outreg to format/generate a m…
Subscribe to:
Post Comments (Atom)
0 Response to Transform data or use a non-parametric analysis
Post a Comment