Z-test in SPSS (was: Re: hypothesis testing for difference between two means)

[Johnny Amora]

Jimjohn wrote:

<<Thanks for all the responses guys. Johnny, I appreciate you explaining how
the grouping variable works. Just one follow up question, I understand if I
go to Compare Means -> Independent Test, then this will conduct a t-test to
compare means. My sample size is about 36, I believe if the sample size is
>30, a z test should be used. Any ideas if SPSS can do a Z-test too to
compare means?

 

There is no (direct) Z-test in SPSS.  Just use T-test, instead.  You dont need to use Z-test because the T approaches Z as n approaches infinity. (That is, the T=Z for large n).  Is your sample size enough?  The rule of thumb for sample size is 10 to 20 cases per variable.  You should also consider the outliers, missing values of your raw data.  You should not forget to do some diagnostic tests of your regression model,  The regression page of UCLA might be helpful to you: http://www.ats.ucla.edu/stat/spss/webbooks/reg/default.htm

 

Hope this helps.

Johnny

 

 

--- On Mon, 5/11/09, jimjohn <[hidden email]> wrote:

From: jimjohn <[hidden email]>
Subject: Re: hypothesis testing for difference between two means
To: [hidden email]
Date: Monday, 11 May, 2009, 10:46 PM

Thanks for all the responses guys. Johnny, I appreciate you explaining how
the grouping variable works. Just one follow up question, I understand if I
go to Compare Means -> Independent Test, then this will conduct a t-test to
compare means. My sample size is about 36, I believe if the sample size is
>30, a z test should be used. Any ideas if SPSS can do a Z-test too to
compare means?

To the posters who posted before, thanks for the suggestions. I would
normally do exactly what you guys recommended, but the circumstances are
different here. Someone else has already performed an analysis claiming that
there is a difference between the two means, that the <$1000 certificate
customers are more sensitive to interest rate changes than the >$1000
certificate customers. Since this is not an intuitive conclusion, I wanted
to run this test to see if the results are significant.






Johnny Amora wrote:
>
> At 10:32 AM 5/8/2009, jimjohn wrote:
>>does anyone here know how to compute hypothesis tests/confidence intervals
>>for the difference between two means in SPSS? For example, I am comparing
>>the volume growth of my certificates with balance less than $1000 versus
the
>>volume growth with balances greater than $1000. I want to see if the
>>difference in the two means is statistically significant. Any ideas? I
don't

>>think comparing means does it because it has something about grouping and
>>factors. thanks!
>>--
>
> You can use the Independent Sample TTest procedure. You should have
> numeric variables for GROWTH and BALANCE where GROWTHÂ as your test
> variable and BALANCE as your grouping variable.  The BALANCE should be
> coded for example as follows: 1= balance less than $1000 and 2 = greater
> than $1000.  Then run the synax:
> Â
> T-TEST GROUPS=BALANCE(1 2)
>   /MISSING=ANALYSIS
>   /VARIABLES=GROWTH
>   /CRITERIA=CI(.95).
>
> The confidence interval (CI) can be changed to what you want, say .99.Â
> Hope I understand correctly your need.
> Â
> Cheers,
> Johnny
>
>
>       Yahoo! Mail Now Faster and Cleaner. Experience it at
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