Complex Between Subjects ANOVA

Question 1

interactions

Answer 1

• It’s an interaction between the IVs on the DV
  
  • The IVs don’t interact with the DV
    Keep in mind how you would report a main effect; we always speak in terms of the effect that IVs have on a DV, and interactions do not change this
  • Note that you won’t be tested on 3-way interactions in PSYC234, so don’t stress too much if it’s quite tricky to interpret
  • However, it’s important to know, as research commonly involves 3+ way ANOVA

Question 2

complex between subjects designs

Answer 2

• A key disadvantage of purely between-subjects designs is that you only have a single measurement per participant
• In purely within-subjects designs, as you increase the number of conditions, you don’t necessarily need to increase the number of participant
  
  • After all, the participants will also participate in these conditions
  • Of course, you do need consider order effects, though
• However, for purely between-subjects designs, your power will massively suffer if you start adding IVs (or more levels of IVs) without adding more participants
  As a (very) rough rule of thumb: 30 participants per cell to detect a moderate to large effect size

Question 3

what to do in R

Answer 3

• Step 1: Install (if necessary) and load in necessary packages
• Step 2: Load the data
• Step 3: Look at and format the data
• Step 4: Test assumptions
• Step 5: Run the ANOVA (regular old ANOVA again)
• Step 6: Get the important information
• Step 7: Run post-hoc tests
  Step 8: Get the important information

Question 4

summary

Answer 4

• “Complex” designs, in this context, refer to designs with 2 or more Ivs
• Complex Between-Subjects Designs are usefully for avoiding potentially dangerous order effects
• However, the more cells you add to the design, the more participants you need, otherwise power will get low very quickly
• Like all Complex ANOVA, we need to break down significant main effects with 3+ levels, and significant interactions, to understand where the differences are
  … 3-way interactions are hard to interpret…