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I ran a study to compare 2 different computer interfaces (say A and B) meant to be used in an unfamiliar environment.

I want to compare:

  1. How much effort participants took to complete a certain task when using the interface for the first time.
  2. How much easier or harder it is for participants to complete the same task the second time they use the interface.

The study procedure:

  • Every participant used either interface A or interface B [Variable: type of interface, 2 levels: A or B, between-subjects]
  • Every participant used the interface (either A or B) to complete the same task twice. (Most) participants did the two tasks on separate days. [Variable: time of task, 2 levels: T1 and T2, within-subjects]
  • Since the environment needed to be unfamiliar, the environment participants did the task in changed each time they did it. The order of the environment was counterbalanced: Some participants did the task in environment 1 first (at T1) and then in environment 2 (at T2), and others did the task in environment 2 first (at T1) and then in environment 1 (at T2). [Variable: environment, 2 levels: E1 and E2, within-subjects, counterbalanced]
  • The measure of "effort" is a continuous variable.

What statistical tests should I use to understand:

  1. The effect of the interface (A vs B) on effort?
  2. Which interface got easier with time (the difference in the effort of using a particular interface between T1 and T2)?

I'm primarily confused because I could consider this a mixed-factorial design with the interface and the environment as the independent variables. However, I don't really care for the effect of environments - the change in environment was just to ensure it stays unfamiliar during both tasks. What I really want to understand is the the impact of the interfaces and time.

Would I use a two-way mixed ANOVA and post-hoc tests? If so, which ones would give me what I'm looking for? If not, what should I be using?

I will be using SPSS for analysis.

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