Programming the statistical procedures from SAS

Student's T in proc univariate

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Student's T in proc univariate

Hi,

 

 I would like to understand the meaning of  T Student result in a proc univariate.

 I  am executiing a proc univariate to know the distrubution of a var:

 

proc univariate data=tabsas.consumo normal plot;
var hc_consumo;
histogram hc_consumo/normal (color=red W=5);
run;

 

In the resullts  get:


Tests : Mu0=0
T Student 33,00654 p valor < 0,001

 

I don't have a statistics background ; i have a basic level,  Can anybody helep me??

I have read about T Student, but I don't understand the relation with the result I get...

 

Any advice will be greatly appreciated

 

Thanks


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‎07-20-2016 05:37 PM
Super User
Posts: 19,194

Re: Student's T in proc univariate

It's a hypothesis test, where the hypothesis is that Mu0 is 0. 

 

Read ad up on basic hypothesis testing here:

https://onlinecourses.science.psu.edu/stat200/node/54

 

And find annotated output for proc univariate here:

http://www.ats.ucla.edu/stat/sas/output/univ.htm

 

Additionally, the statistics in SAS e course is free and on demand. 

http://support.sas.com/training/tutorial/

 

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‎07-20-2016 05:37 PM
Super User
Posts: 19,194

Re: Student's T in proc univariate

It's a hypothesis test, where the hypothesis is that Mu0 is 0. 

 

Read ad up on basic hypothesis testing here:

https://onlinecourses.science.psu.edu/stat200/node/54

 

And find annotated output for proc univariate here:

http://www.ats.ucla.edu/stat/sas/output/univ.htm

 

Additionally, the statistics in SAS e course is free and on demand. 

http://support.sas.com/training/tutorial/

 

Frequent Contributor
Posts: 121

Re: Student's T in proc univariate

I understand that you make this test, to know is the mean value of the var is represetative, if it represents well the values of the var, in't it??

Super User
Posts: 19,194

Re: Student's T in proc univariate

No, it's a test to see if the mean value is different than 0.

Frequent Contributor
Posts: 121

Re: Student's T in proc univariate

Ok, there must be something I don't understand. If I get a mean value of 35,6 (fo9r example , Why do I do a test to  know if it is different from 0?

 

I don't undrestand the objective of this test...,  there must be something  I don't get..

Super User
Posts: 19,194

Re: Student's T in proc univariate

Because the means is a single measure. You DON'T KNOW that it is actually different than 0.

 

Here's an example, extreme, but illustrates the issue of an outlier. 

 

data sample;
	do i=1 to 10;
		x=rand('normal', 0, 2);
		output;
	end;
	x=350;
	output;
run;

proc univariate data=sample;
	var x;
run;

Output:

 

Tests for Location: Mu0=0
Test Statistic p Value
Student's t t 1.002908 Pr > |t| 0.3396
Sign M 0.5 Pr >= |M| 1.0000
Signed Rank S 7 Pr >= |S| 0.5771

 

In this case the test tells you the mean is not significantly different than 0, although the mean is ~32.

Super User
Posts: 19,194

Re: Student's T in proc univariate

Anscombe's Quartet is a good example of relying on statistics.

 

https://en.wikipedia.org/wiki/Anscombe%27s_quartet

Occasional Contributor
Posts: 14

Re: Student's T in proc univariate

Hi Reeza,

 

Would you know if it is possible to adjust the default mean (mu0) value from 0 to my own hypothetical mean as I want to test if my sample lie close to a hypothetical mean using the t-test.

Thanks

Priya.

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