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

[Erik Iverson]

Robert, 

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.

Hi,
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)
0.6000000238
0.8000000119
0.6000000238
0.2000000030
0.6000000238
...
...

sample2: (total 188 samples)
0.80000001
0.20000000
0.80000001
0.00000000
0.80000001
0.40000001
...
...

I want to check if these results are statistically significant? Intuitively,
the similarity in the two results mean the results are statistically
significant.
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
close!)
Please help me interpret the results..
thanks in advance!

--
Rob Hall
Masters Student
ANU

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