Updating your counterbalancing shelf

Online experiments
,
1

Hello,

I am currently running an online experiment which is counterbalanced (for 6 different groups) using the shelf. This works successfully - however, I am wondering whether you are able to manually update your shelf group allocation numbers during data collection or whether this will cause issues.

For example, using the shelf, my study currently allows for 20 participants per group, however say I realise I need to exclude some participants - am I able to go back to the groups and increase the number of allocations to make sure I end up with 20 usable datasets for each group? or say I need to reduce the amount in one group because I have enough.

What is the best way to handle this without causing issues?

e.g. If I originally asked for 20 for a group, 5 participants completed so the shelf now says there are 15 spaces remaining. If I manually edit this to say 20 again, will I get 20 participants from that point on - ending up with 25 participants if you include the original 5?

I tried to edit the shelf once before, and one of my groups ended up saying ‘-1’.

2

You can, but make sure that groups and groupSizes have the same length, e.g.

{
  "groups": [
    "Event3",
    "Time3",
    "Event4",
    "Time4"
  ],
  "groupSizes": [
    3,
    4,
    4,
    4
  ]
}