Recent content by obh

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    2 sample z test - Standardized Effect Size

    Thanks Spunky, It is clear that the average of variances doesn't provide the exact population variances. You can see in my response to Ondansetron that the average of variances provide almost correct results in the R demo Anyway my original question was how to calculate the Cohen effect...
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    2 sample z test - Standardized Effect Size

    Good morning Ondansetron. You proved with simulation (nicely) the basic statistics Var(x+y)=var(x)+var(y) and Var(x-y)=var(x)+var(y). thanks for the nice demonstration :) Pool variance is not the variance of (X+Y), but is the entire population variance. When using t-test you treat the 2...
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    2 sample z test - Standardized Effect Size

    The calculation is for the population standards deviation, and not for a combination of 2 random variables (X+Y) or (X-Y) for example, if taking a specific case when variance1=variance2=8, the population variance should be 8, and standard deviation sqrt(8)
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    2 sample z test - Standardized Effect Size

    I guessed you saw t-test :) Cohen's effect size uses the population's standard deviation, not the statistic's standard deviation. The population standard deviation when you mixed 2 groups depends on the number of items from each group in the entire population (not in the samples). But I...
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    How to read Independent Samples T-Test.

    If you use one of the following links you will also get some results interpretation. http://www.statskingdom.com/150MeanT2uneq.html http://www.statskingdom.com/140MeanT2eq.html
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    2 sample z test - Standardized Effect Size

    Hi Ondansetron :) The question is about z-test. Do you mean using the same formula used for the t t-test to the z-test? I think, but not sure that the average of the variances is the correct answer.
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    2 sample z test - Standardized Effect Size

    Thanks hlsmith, Thanks for the book suggestion, I didn't find anything related to the option you know the two samples standard deviations. It is always sample standard deviations from other sources. probably z test is much less practical ... I guess the z test was used more when people used...
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    2 sample z test - Standardized Effect Size

    What are your thought hlsmith ?
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    2 sample z test - Standardized Effect Size

    Hi hlsmith, Per my understanding, the book describes the: 2 sample t test - Standardized Effect Size. When you use the sample standard deviation: S pooled ^2= ( (n1-1)S1^2+(n2-1)S2^2)/(n1+n2-2) The question is how to calculate the 2 sample z test Cohens effect size, when you know the...
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    2 sample z test - Standardized Effect Size

    Thanks hlsmith I can't see this page, do you recommend to buy this book?
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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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    How to compare population distribution?

    Correct... I didn't notice it is a full population data
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    How to compare population distribution?

    Hi Abhishek, ANOVA assumed normality (but not sensitive for normality if symmetric) I think the equivalent non-parametric test for ANOVA check if the data came from the same distribution: Kruskal–Wallis test
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    Forecasting percentages

    In logistic regression, the dependent variable (Y) is a categorical variable, for example, succeed shot or missed a shot. And the regression will calculate the probability for evet value od Y. But I'm not sure if you will have enough data to create the regression especially when the dependent...
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    Forecasting percentages

    What about logistic regression?