Independent samples and paired samples
Independent samples
Independent samples are those samples selected from the
same population, or different populations, which have no effect on one another. That is, no correlation exists between the samples.
Example
Paired samples
In paired samples, each data point in one sample is matched to
a unique data point in the second sample.
An example of a paired sample is a pre-test/post-test study design in which a factor is measured before and after an intervention.
18-03-2014
Instituto Superior de Estatística e Gestão de Informação - Universidade Nova de Lisboa
2
Sign test (157-164)
The sign test
Conditions of Use: Use the sign test when you have one sample
of subjects with some measure repeated on each subject (e.g. before and after scores) and you can not use a repeated measures t-test
(because one of the assumptions of the t-test has been violated, but the assumptions of the sign test for the same data are not violated).
The data consist of observation on a bivariate random sample
(X1, Y1), (X2, Y2), …. (Xn, Yn), Where there are n pairs of observations. Within each par (Xi, Yi) a comparison is made, and the pair is classified:
– “+” if Xi < Yi ; – “-” if if Xi > Yi ; – “0” IF if Xi = Yi ;
18-03-2014
At least ordinal scale
Instituto Superior de Estatística e Gestão de Informação - Universidade Nova de Lisboa
3
Sign test (157-164)
1. Assumptions
Two paired samples
The bivariate random variables (Xi > Yi ), i=1,2,…,n, are mutually
independent. The measurement scale is at least ordinal within each pair. That is, each pair (X1, Y1) may be determined to be a “plus,” “minus,” or “tie.” The pairs (Xi, Yi) are internally consistent, in that if P(+) > P(-) for one pair (Xi, Yi), then P(+) > P(-) for all pairs. The same is true for P(+) > P(-), and...
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