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    Chi square effect size - why to use the Crammer's V and not only Phi

    Hi The recommendation: For the goodness of fit, or table 2*2: Phi=sqrt(χ2/n) For association: DF'=min(row-1,cols-1) Crammer's V=sqrt(χ2/(n*DF') But also the definition of small/,medium/large is divided by sqrt(DF') For example DF'=1 it is (0.1-small, 0.3- medium, 0.5 - large) For DF'=2 it...
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    Minimum Sample size for multiple linear regression

    Hi, I tried to calculate the minimum sample size for multiple linear regression. I tried to check the sample size for predictors=4, effect size f=0.2/d=0.2, sig.level =0.05, power=0.8 1. When I checked the power of the entire model (F power) n=304 2. When I checked the power of one...
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    CLT - What sample size is large enough? your thoughts?

    Hi, I will glad to read your thoughts Whats sample size is large enough so I can assume normality based on the Central Limit Theorem? Some write 30 some write 100. I run some simulations and it seems that for some skewed data (finite variance, independent ...) you need a sample bigger than...
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    Tukey HSD/ Kramer for Levene's test?

    Hi, Usually, people only want to know about the equal variances assumption. A theoretical question, since the Levene's test is actually a one way ANOVA test over the differences from the averages/medians I assume you can use the Tukey HSD/ Tukey Kramer also to know which variances are not equal?
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    Binomial exact test - calculate p-value of two tailed test

    Hi, In the below example 1, (x=2, n=20, p=0.25) two tailed test. I would expect the p-value of the two-tailed test to be 2* p(X≤2)=2* 0.09126043=0.18252086 I understand that probability in the right tail is discrete so it can be 0.101811857 or 0.040925168 So it seems that in R takes the value...
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    Test priori power - Welch T test

    Hi All, I didn't find the answer for how to calculate the prioir power of Welch's t-test directly. some suggest using a simulation. I know that calculate the power for "pooled variance t-test" should also give a reasonable estimation for the Welch's t-test . the power of "pooled variance t...
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    2 sample z test - Standardized Effect Size

    Hi, comparing the average of 2 groups when we know each group's standard deviation: σ1, σ2 Cohen’s effect Size = | avg(x1)- avg(x2)| / σ pooled How do you calculate the σ pooled for 2 sample z test? σ pooled^2= (n1σ1^2+n2σ2^2)/(n1+n2) {similar to t-test} or just a simple average σ...
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    Multinomial Logistic Regression - when to exclude predictor

    Hi Multinomial Logistic Regression With 3 predictors X1, X2, X3 and 3 possible values for the dependent variable Y: A, B, C When you build the model before getting the results you aren't sure if X3 should be in the model. X3 is significant for ln(Pb/Pa) , but is insignificant for ln(Pc/Pa)...
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    Shapiro wilk effect size

    Hi, Do you know how to calculate the effect size for Shapiro Wilk test? When using Shapiro Wilk test on a large sample, most likely it will reject H0 even for normally distributed population, since large sample will identify the minor effect as significant. Thanks :)
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    Royston approximation for Shapiro-Wilk normality test

    Hi, Shapiro-Wilk article support tables only for n<=50. Patric Royston support calculations for a(i) and P-value based on W for n<=2000. and probably ok for n<=5000 in the following article "Approximating the Shapiro-Wilk W-test for non-normality" Are the values in Shapiro-Wilk article also...
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    T Test

    Hi T-Test is used instead of Z-Test when we don't know the standard deviation, or when the sample size is too small (less than 31) When we know the standard deviation but the sample size is small, do we use T-Test with sample standard deviation (S)? or T-Test with the known standard deviation...