## 2 sample t-test: real data against group with M=0 and SD=1?

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kforkmann
Posts: 2
Joined: Tue Aug 07, 2012 7:56 am

### 2 sample t-test: real data against group with M=0 and SD=1?

Hi there,

we want to use SPSS to compare two groups (2 sample t-test, independent samples). The first group contains real data, the other group is fictional. This fictional group should contain as many "subjects" as the real (1st) group. But the mean is set to 0 and the standard deviation to 1 (standard normal distribution).

There are several tools like http://in-silico.net/tools/statistics/ttest/ out there to compare two groups by adding the number of subjects, mean and std for every group independently. But how can we do this in SPSS? I only know how to test one variable (group1) against a test value (T=0).

I'm a blockhead right now. Any help is greatly appreciated!

Cheers!
Kati
Penguin_Knight
Posts: 473
Joined: Thu Apr 05, 2012 5:58 pm

### Re: 2 sample t-test: real data against group with M=0 and SD

You can compute one by using the "RV.NORMAL(0,1)" function under Transform > Compute. And then you can restructure the data so that it's fit for independent samples t-test.

What's more concerning is: what kind of test is that? What exactly do you want to achieve?
kforkmann
Posts: 2
Joined: Tue Aug 07, 2012 7:56 am

### Re: 2 sample t-test: real data against group with M=0 and SD

Hi, thank you for the answer!
Yes, this kind of approach seemed strange to me too. But the thing is that we investigated 20 patients and compared their data with a large database of healthy control subjects. That means we did a z-transformation using the reference database (standard procedure in this field (quantitative sensory testing=QST)).

There are other research groups which suggest to then use the 2-sample t-test I mentioned below, because it would be inappropriate to compare data of 20 patients with data of 1200 controls.
So they invented a fictional group with M = 0 and SD = 1 and tested the real data against this fictional data (on a website like http://in-silico.net/tools/statistics/ttest/ --> but Two-Sample T-Test).

To be honest, I have no idea if this is the right approach. My first idea was to do a one-sample t-test and test the patient group (i.e. their z-values) against the value 0 to see, whether the z-values differ significantly from 0.

What do you say?
Kati

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