Composite decking is increasingly popular, as it requires little maintenance. Options include polyethylene (with an average cost per square foot of $7.82), polypropylene (average cost per square foot, $8.68) and polyvinyl chloride or PVC (average cost per square foot, $7.50 hollow core, $9.48 solid core.) Pros. Composite materials are very durable, and won't splinter or rot.
Two-sample t-tests for a difference in mean involve independent samples or unpaired samples. Paired t-tests are a form of blocking, and have greater power than unpaired tests when the paired units are similar with respect to noise factors that are independent of membership in the two groups being compared.
The independent variable is independent because its variation does not depend on the variation of another variable in the experiment/research project. The independent variable is controlled or changed only by the researcher. This factor is often the research question/hypothesis behind the outcome of the experiment. In the above example, the researcher may have wanted to see if participating in the training program raised students' scores on a final test.