Re: one sample t-test --> nonparamatric equivalent?


There is research justifying the treatment of Likert
data as interval
rather than ordinal. If you search an archive of
this list, you should
find a thread from a couple of months or so ago.

Thank you Paul. I actually do have a number of sources I can reference on why Likert data is sometimes treated as interval. It is just that my supervisor (who will mark my work) suggested to use non-parametric tests, because that would not have to make the interval data assumption.


That said, I think you could subtract 3 from you
observations and then
use the Wilcoxon signed rank test, which would test
whether the median
response was three or not.

I tried to use the Wilcoxon signed-rank test with a 2nd (dummy) set of values all set at 3 and I get sig. = .190 in my example.

Using the Mann-Whitney test I get sig. = .222 (which feels like the better alternative, since the sample is independent, at least I think so)

Using the one sample t-test (comparing to 3) I get sig. = .211

So roughly they produce similar significance. I also ran (with my test data) a Kolmogorov-Smirnov test to check for normality (to be able to use the t-test) and with K-S sig. = .104 I would be able to argue for normality, and consequently for the use of the one sample t-test, right?


/Paul

Thanks for your help,

Anatol
.

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