Item numbers the same accross trials?

[carlap]

I ran an experiment in 2020 and I cannot remember if the item numbers are the same accross trials. That is, is item #189 always the same question? I know the order is randomized, but I think the item numbers should be conserved?

[Jeremy]

Hi,

It depends on what exactly you mean by item number:

1. there is an Ibex-internal notion of item number, which corresponds to an index in the items array
2. there is a PennController-specific notion of “trial” number, which corresponds to when the PennController trial was created (newTrial commands inside Template commands are executed after non-embedded newTrial commands, so the former have greater trial numbers than the latter)
3. then there is the notion of an item/trial’s runtime number, which would correspond to when the participants saw that trial relative to the other ones; this is not reported by default anywhere in the results file, but you could keep track of that with a global Var element that you increase at the beginning of each trial
4. finally, you could have a column named “item” in your table, whose values you decide how to assign; if you have a latin-square design for example, you could decide to have the same value in multiple rows that correspond to different groups

The numbers associated with points 1 and 2 will be the same across participants: no matter the actual sequence of trials they see, those “item numbers” will always be the same, so the question associated with item #189 in this sense will always be the same. The number associated with point 3 can obviously vary from one run to the other, since it corresponds to the runtime “item number,” so the question associated with item #189 in this sense could vary. As for the number associated with point 4, it will depend on what you decide to do with your design; if you have multiple rows with 189 in the “item” column but a different string in the “question” column, then item #189 will not always be the same question

Jeremy

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