• Statistics

    Choosing a statistical test: A cheat sheet

    Students who are new to statistics tend to find it tricky to remember which test to use under which circumstances. The following diagram is intended as a decision aid only. There are many many more statistical tests that are not shown here, but these are the basic ones most commonly taught on psychology courses. Even if you end up finding out that you need a more complex or niche statistical test, an aide memoire like this can still be useful if it reminds of the relevant keywords to search. Remember, always check the assumptions of the test you choose.

  • Statistics

    Alternatives to pro-rating for missing data

    Behavioural scientists often collect data using multi-item measures of latent constructs. For instance, clinical psychologists measure anxiety and depression using self-report questionnaires composed of multiple psychometric items, whilst child psychologists measure developmental progress by asking parents batteries of questions. Missing data are extremely common on such questionnaires, and one usually finds that data are missing at the item level. In other words, participants miss out items, either by accident, or because they don’t want to answer certain questions. Thus, researchers are left with some data relating to a given construct for a particular participant, but not complete data. The usual solution is pro-rating, where the mean of the completed items…

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    Computing variables and pro-rating in SPSS

    The basics SPSS allows you to compute new variables, based on existing ones. This is really useful if, for instance, you want to create a total score for a psychometric scale or other questionnaire. ⚠️ Be sure to read this post on assumption checks you should perform. You access the Compute Variable dialogue box from the Transform menu… Here’s what each part of the window is for… Now let’s say that you want to simply add up three variables to make a total score. You just need to type a sensible name in the left-hand column, and then pace each of the variables in the right-hand ‘Numeric Expression’ box, with…