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.
There are often not more than one or two independent variables tested in an experiment, otherwise it is difficult to determine the influence of each upon the final results. There may be more than several dependent variables, because manipulating the independent can influence many different things. For example, an experiment to test the effects of a certain fertilizer, upon plant growth, could measure height, number of fruits and the average weight of the fruit produced.