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## Big Ten Confounds

In any experiment there is the possibility that extraneous variables, rather than the independent variable(s) are producing the change on the dependent variable (a confound or threat to internal validity). If the extraneous variable cannot be eliminated it must be...

## Partial Correlation

In an earlier entry, I discussed types of correlation coefficients for variables with different scales of measurement. In this entry, I want to discuss correlation coefficients that are used with three or more variables. These coefficients are known as partial and...

## Mediators and Moderators

One of the most confusing concepts in research is the distinction between mediators and moderators.A mediator ‘mediates’ the relationship between two variables (the independent and dependent variables). That is, the two variables are correlated, but their relationship...

## Correlation Coefficients

There are many different ways to calculate how much two items are associated. The calculation of these correlation coefficients depend on how the items are measured. That is, the calculation depends in part on whether the items are measured on a nominal, ordinal,...

## One and Two-Tailed Tests

When you conduct a test of statistical significance, whether it is a t-test, correlation, an ANOVA, or regression, you are given a p-value in the output. Almost always, this p-value is for a two-tailed test.If you are using a significance level of .05, a two-tailed...