I wish to conduct an experiment where I have a number of different groups, let's say four groups of X people each. Each person in each group partakes in a similar experiment, with each group testing a different value of the variable I want to test.
For example: Everyone plays a game of Pacman. For each group, the ghosts have different colors. I want to research if these colors affect the player's performance (score).
Now my question is first, is this possible in any way? And if it is, what conditions do I need to fulfill? I assume the groups need to be similar, so I can't have one group consisting of only students, and one group consisting of only 90-year-olds, but what would the exact criteria be?
I could also let everyone test each of the four settings, but I'm worried previous tests will affect the results of latter ones (for example, people get better at Pacman and perform much better the fourth time). Besides that, each experiment would take four times longer.
So is it possible to compare different groups with a slightly different scenario each? If so, how? If not, what would be a better option?