How to Conduct One-Tailed Column Comparisons

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By default, Column Comparisons in Q are all two-tailed. However, they can be converted to one-tailed tests by modifying the significance levels. This modification can either be done for an entire project or specific tables in a project.

Modifying the significance levels for the entire project

  1. Edit > Project Options > Customize > Statistical Assumptions.
  2. Enter a value into the Overall significance level that is double your desired level. For example, if you are wanting to do a one-tailed test at the 0.05 level (95% level of confidence), enter 0.10 (i.e., 2 * 0.05) into the box.
  3. Make appropriate adjustments via cutting and pasting of the Column Letters column in Significance levels and appearance, and, if necessary, adding or deleting new rows by pressing the green + and red - buttons.

Example: Testing at the 0.05 level (95% level of confidence)

OneTailedOne.PNG

Example: Testing at the 0.10 and 0.05 levels (90% and 95% levels of confidence)

OneTailedTwo.PNG

Modifying the significance levels for a particular table

This is exactly the same as with Modifying the significance levels for the entire project, except that:

Multiple comparison corrections

Generally one-tailed tests are conducted in situations where there are clear a priori hypotheses regarding the likely results. In such situations it may be advisable to turn off any Multiple Comparison Corrections.

Modifying footers

The footers need to be updated to show that you have conducted one-tailed tests. This is done as follows:

  • Select all the tables where you are conducting one-tailed testing (select all the tables in the project if you are applying one-tailed testing to the entire project).
  • Edit > Table Options > Footer
  • Replace the contents of the Significance Testing > Text with whatever you wish. For example, One-tailed test at 90% level of confidence.

See also

How to Specify Columns to be Compared