One Tailed vs Two Tailed

The tails referred to in your statistical package are the nonwagging variety; the term represents the tail edges of the bell-shaped normal distribution. Tests are one- or two-tailed depending on whether they compute the probability of values exceeding the range expected from members of a population in only one direction or potentially in both directions (i.e., greater than or less than).

Using a one-tailed test is justified only if there was an a priori determination that only differences in one specified direction would be assessed, not because one decides after seeing that the one-tailed p is significant but the two-tailed is not, that one only really cares about one direction anyway. Furthermore, having an expectation that the difference to be found will go in a particular direction is not considered adequate justification for performing one- t ailed analysis; rather, one-tailed analysis could be considered appropriate if having a large difference in one direction vs. having no difference at all would have equivalent consequences [39] - Under most circumstances a two-tailed test is the appropriate choice, and if the researcher is in any doubt about which is appropriate, the two-tailed should be chosen.

Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

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