topic Re: pooled /unpooled t test in Discussions

pooled /unpooled t test

Alma1 — Sat, 10 Jun 2023 20:37:43 GMT

What is the appropriate two sample t procedure for the summary below milking periods of cow breeds pooled/unpooled (Welch) using R?

Frisian cow Xbar=342.5 S1=10.2 n1=126

Jersey cow Xbar =348.6 S2=12.2 n2=39

Construct 95% confidence interval for µ1-µ2

Give proper interpretation of the interval

Thanks

Re: pooled /unpooled t test

txnelson — Sat, 18 Jul 2020 04:36:38 GMT

Is this a homework exercise?
Why are you asking the JMP community to answer a question that is directed for a solution using R?

Re: pooled /unpooled t test

Georg — Sat, 18 Jul 2020 10:02:14 GMT

@Alma1 have a look at

help -> sample data -> Calculators -> Hypothesis test for two means

and follow the workflow (or excecute the script below).

For learning Purpose I would also recommend to construct a data table from the summary statistics and perform the t-Test from menu Analysis -> Fit y by x, and Read the explanations JMP gives.

Names default to here(1);
open("$SAMPLE_SCRIPTS\Calculators\TestTwoSampleMeans.jsl");

Re: pooled /unpooled t test

Alma1 — Sat, 18 Jul 2020 13:26:34 GMT

Nop! it is not a homework. we are conducting a research and I didnt know whether to use pooled /unpooled test whats wrong asking for ideas? you are free not to answer if you wish

Re: pooled /unpooled t test

Alma1 — Sat, 18 Jul 2020 13:29:52 GMT

by the way jmp background is R.

Re: pooled /unpooled t test

Georg — Sat, 18 Jul 2020 13:33:58 GMT

Unpooled is needed when variance is different

Re: pooled /unpooled t test

Jeff_Perkinson — Sat, 18 Jul 2020 16:59:47 GMT

@Alma1 wrote:

by the way jmp background is R.

I'm not sure exactly what you're thinking of here but JMP has no background with R.

JMP is a product from SAS and is developed solely by us.

There is integration with R through JSL, providing the ability to call R and submit R code but that's the only association between JMP and R.

Re: pooled /unpooled t test

Alma1 — Wed, 22 Jul 2020 05:09:26 GMT

I do not think of anything that might harm you or any other person. I meant integration why is it this much important I just used wrong wording, but this raised because one of the users interrupted me by questioning my question. Any person has the right to ask any scientific question and the viewers can choose to answer or ignore. What is wrong! Why is he even asking if the question is a homework is this something related to him? Do researchers have homework?!
I would suggest keeping up the academic value and providing help if needed instead of bothering what is asked.

Re: pooled /unpooled t test

Alma1 — Wed, 22 Jul 2020 05:13:04 GMT

Georg thanks for your response. Do you mean population variance and should we calculate it before deciding on a pooled / unpooled test?

Re: pooled /unpooled t test

Georg — Wed, 22 Jul 2020 10:57:59 GMT

@Alma1 , I do not know what data you have, an example would be helpful.

In the below script (when you execute) you see a dataset and both t-test performed, giving different results.

Generally, statistical Tests have preconditions, and t-test assumes normal Distribution of the dataset,

pooled t-test assumes equal variance,

t-test works also with different variance.

This is because they work with mean and variance, and if that two numbers do not represent the data correctly, the method doesn't work.

If you perform a t-test, and the assumptions are not valid, you cannot rely on the result.

In the below example you can see different results for both t-Tests, but be Aware, that normal Distribution is also not valid in this case.

You can find These results in the documentation also, and I found STIPS a quite good training to understand this stuff.

Names Default To Here( 1 );
cdt = Open( "$SAMPLE_DATA\companies.jmp" );

cdt << Oneway(
	Y( :Name( "Profits ($M)" ) ),
	X( :Type ),
	Means( 1 ),
	t Test( 1 ),
	Mean Diamonds( 1 ),
	SendToReport(
		Dispatch( {"Oneway Anova"}, "Summary of Fit", OutlineBox, {Close( 1 )} ),
		Dispatch( {"Oneway Anova"}, "Analysis of Variance", OutlineBox, {Close( 1 )} ),
		Dispatch( {"Oneway Anova"}, "Means for Oneway Anova", OutlineBox, {Close( 1 )} )
	)
);

Re: pooled /unpooled t test

Alma1 — Wed, 22 Jul 2020 23:33:36 GMT

million thanks for your help