Please! I need some help
Hi,
I posted some like my questions, but I didn't stay very clearly with my problem.
I have some rows of data like
I need to apply some tests to compare if the first 3 elements have the same distribution than the other 3. I have some rows with big numbers likeCode:1 0 2 1 3 0
My idea is to test the normality of each row and if the row has a normal data, I will apply normal tests. If the row don't have normal data, I will apply not normal tests.Code:23 32 12 33 23 54
Is correct what I'm thinking to do? My question is because I only have 6 data for each row...is correct to apply a shapiro.test to test the normality?
Thank you very much
Please! I need some help
Your original question is a little unclear. Can you take sometime to rephrase it, so we better know what you are doing and the purpose.
Also it may be helpful for you to read about Kolmogorov–Smirnov test.
Stop cowardice, ban guns!
My original question: I need to compare if the groups(3 first elements and last 3) has the same distribution. For to do this I need to apply some statistical tests, but first I need to know if I have a normal data.
Which is the difference between the two tests (kolmogorov smirnov or shapiro.test) in this case?
What do you do if you have a non-significant Shapiro-Wilks but a significant kolmogorov smirnov ? If kurtosis and skewness are less than +/-1 . Can I use a repeated measure ancova?
QQ plots are commonly used (and are probably the best way to determine) normality of data. Although I have never seen this done (interestingly) I assume this could be done with residuals just as easily as raw data.
Its interesting that QQ plots are commonly shown with raw data not residuals even with methods like ANOVA or regression that make assumptions about the normality of the residuals not the raw data.
"Very few theories have been abandoned because they were found to be invalid on the basis of empirical evidence...." Spanos, 1995
Thank you.
The better thing is to do a QQ-plot. But with this, can I have a measure? A number? Or only the graph? Because I need to apply this to a lot of rows, and it´s impossible to look all the graphs...
After that (and I know that the the power of the test isn't good), can I apply the test (normal or not normal) to see the distribution?
QQ plots only plot the observed data against a theoretical distribution. They don't calculate a test statistic.
I am not sure what you mean by a lot of rows. Regardless of how many variables you have the residuals (your observed data) will be a single set of data so you can use one QQ plot.
"Very few theories have been abandoned because they were found to be invalid on the basis of empirical evidence...." Spanos, 1995
"A lot of rows": a lot of data to test the normality. I asked if it's possible to have a "value" for the QQ plot because I need to do test for about 20000 rows of data (independently) and it's impossible to look all graphs. If I have a number, I can filter, it's beacause I talk about shapiro.test or kolmogorov-smirnov.
In this case I need to work with one of that(shapiro.test or ks.test). Which is the best? Or more correct to use?
Thank you
As far as I know QQ plot's don't generate a statistic or value you can test.
In all the discussions of various normality tests I have not seen authors come down on one as being better. The general comment is that all are weak in terms of statistical power.
"Very few theories have been abandoned because they were found to be invalid on the basis of empirical evidence...." Spanos, 1995
I know the power is very bad, but it's correct to do a shapiro.test or ks.test? Or there are some rules that I can't apply this?
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