[R] T-test to check equality, unable to interpret the results.

Erik Iverson eiverson at NMDP.ORG
Wed Sep 16 21:03:58 CEST 2009


We unfortunately do not have enough information to help you interpret the results, and this is not really an R question at all, but general statistical advice.  You will probably have much better understanding and confidence in your results by consulting a local statistical consultant at your university.

The values shown for sample 1 and sample 2 lead me to believe that these are not drawn from a homogeneous population.  Whoever ends up helping you is going to need to know how these measurements were obtained in much greater detail than you've given here. 

Best Regards,
Erik Iverson 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Robert Hall
Sent: Wednesday, September 16, 2009 1:55 PM
To: r-help
Subject: [R] T-test to check equality, unable to interpret the results.

I have the precision values of a system on two different data sets.
The snippets of these results are as shown:

sample1: (total 194 samples)

sample2: (total 188 samples)

I want to check if these results are statistically significant? Intuitively,
the similarity in the two results mean the results are statistically
I am using the t-test t.test(sample1,sample2)to check for similarity amongst
the two results.
I get the following output:

    Welch Two Sample t-test

data:  s1p5 and s2p5
t = 0.9778, df = 374.904, p-value = 0.3288
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -0.03170059  0.09441172
sample estimates:
mean of x mean of y
0.5138298 0.4824742

I believe the t-test checks for difference amongst the two sets, and p-value
< 0.05 means both thesets are statistically different. Here while checking
for dissimilarity the p-value is 0.3288, does it mean that higher the
p-value (while t.test checks for dis-similarity) means more similar the
results are (which is the case above as the means of the results are very
Please help me interpret the results..
thanks in advance!

Rob Hall
Masters Student

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