Linked Questions

105 votes
10 answers
51k views

What is a complete list of the usual assumptions for linear regression?

What are the usual assumptions for linear regression? Do they include: a linear relationship between the independent and dependent variable independent errors normal distribution of errors ...
tony's user avatar
  • 1,059
62 votes
3 answers
248k views

ANOVA assumption normality/normal distribution of residuals

The Wikipedia page on ANOVA lists three assumptions, namely: Independence of cases – this is an assumption of the model that simplifies the statistical analysis. Normality – the distributions of the ...
Roman Luštrik's user avatar
29 votes
3 answers
63k views

What should I check for normality: raw data or residuals?

I've learnt that I must test for normality not on the raw data but their residuals. Should I calculate residuals and then do the Shapiro–Wilk's W test? Are residuals calculated as: $X_i - \...
abc's user avatar
  • 1,811
8 votes
4 answers
2k views

If a statistic doesn't reveal a significance, do I have to calculate power for it?

Following the design and data described in this question, I did a simple one-way within-subjects repeated-measures (RM) ANOVA and found some significant p-values. I then applied non-orthogonal post-...
abc's user avatar
  • 1,811
1 vote
2 answers
15k views

Testing normality assumptions for linear mixed models and mixed (repeated) GLM ANOVA in SPSS

I have a mixed design that includes both repeated (condition) and between (sex and genotype) subjects factors. I would like to assess whether my data meets the normality assumptions for 1) General ...
PatrickSB's user avatar
0 votes
1 answer
9k views

How to calculate 95% confidence interval for the differences of means in R? [closed]

Here I described my general situation. How to calculate 95%CI between means in R?
abc's user avatar
  • 1,811
3 votes
1 answer
2k views

Should raw data or residuals be used to check homogeneity of variance?

Unexpectedly for me (!) I've recently learnt that: "We have assumed that the error terms, $\epsilon_{ij}$, of the variates in each sample will be independent, that the variances of the error terms ...
abc's user avatar
  • 1,811
4 votes
1 answer
3k views

How to choose an appropriate covariance structure for a simple one-way within-subjects RM ANOVA design?

It is postulated that one of the main issue is to find an appropriate covariance structure for repeated measures designs [Ref1]. SAS' PROC MIXED contains a number of covariance structures. Despite "...
abc's user avatar
  • 1,811
3 votes
2 answers
1k views

If I count cells should I consider them as Poisson distributed?

I calculate (with flow cytometry) pecentage of lymphocytes with a specific receptor (Lph*) as a ratio to general number of lymphocytes (Lph). Should I consider them (Lph*) as Poisson distributed? (My ...
abc's user avatar
  • 1,811
3 votes
0 answers
3k views

Is Freeman — Tukey's transformation the most powerful for percentages?

I've described a typical design for my experiments in this question. Well, 1-way RM ANOVA assumes a Gaussian distributed vector. I try $y=\arcsin{\sqrt{x}}$. But for some data it works, for some doesn'...
abc's user avatar
  • 1,811
1 vote
1 answer
1k views

What type of error correction do I have to use after Wilcoxon matched pairs test?

Do I have to use Bonferroni's or Holm's corrections? Please see this previous question for my example data and the design. (Shortly, I have three or more dependent groups.)
abc's user avatar
  • 1,811