Millisecond Forums

subject numbers not sequential and repeated

https://forums.millisecond.com/Topic13534.aspx

By Diane - 6/12/2014

Hi,


I am using participant number to run two different versions of the experiment (using the group attribute). I want equal numbers of odd and even participant numbers in order to have equal numbers for the different versions. After running about 80 participants online I noticed two things that are problematic: 1. Numbers are not assigned sequentially, creating non-equal numbers of participants in different versions. 2. One number has been used for 9 different participants. How is this possible? They participated at different times and even on different days.

I really need equal numbers in the two versions. I can I fix this problem and make sure that if I run 80 participants I get 40 in each version in stead of 30-50 or something like that?


Thanks

Diane
By Dave - 6/12/2014

> 1. Numbers are not assigned sequentially, creating non-equal numbers of participants in different versions.

Every time someone visits the launch page (or decides to refresh it when it's already opened) a new number will be returned. This happens regardless of whether the respective person ultimately decides to actually start the experiment or not. That's the likely reason you might be seeing some gaps and there really isn't anything that could be done to prevent this from happening at present.

> 2. One number has been used for 9 different participants. How is this possible? They participated at different times and even on different days.

It shouldn't be possible provided that everything has been set up correctly. Whether that is the case or not, unfortunately cannot be answered in general terms. You would have to at least provide a link to the respective launch page.[1]

As a general matter, if you want full control over how many people get assigned to each of your conditions, doing the condition assignment beforehand and then passing the respective ID in via URL query parameters would be the way to go.

[1] The only scenario I can think of that would lead to duplicate IDs is if you -- at some point after collecting some data -- took the experiment down and later re-uploaded it. Then ID generation would re-start from scratch and duplicates would be likely to occur, particularly when using sequential IDs.
By Diane - 6/17/2014

I think I discovered the cause of the repeated number problem. Some participants were using the same computer, and in stead of following the URL that I sent them they restarted the experiment from the file in their download folder.

Where can I find instructions on how to set ID via URL query parameters?


Thanks 

Diane
By Dave - 6/17/2014

You'll find use of query parameters covered in the "How to interoperate Inquisit with online survey packages" topic in the Inquisit documentation. (Note: Query parameters can just as well be used without any external survey platform -- it's just the most common use case). It's also been discussed numerous times throughout various threads in this forum -- a search for "query parameters" should turn most of these up. One example:

https://www.millisecond.com/forums/FindPost11934.aspx
By Reshan - 7/18/2016

Hi!

I think I am experiencing the same, or similar, problem of multiple different files of data for the same participant. We identified our participants by asking them to input the last 4 digits of their phone number, and within the final data we found certain numbers had 6 or more files. While duplicated phone numbers are certainly possible, the number of duplicates recorded was improbable. 

Is anyone experiencing a similar problem and have any suggestions for how to fix it or decrease the number of duplicates? 

Thanks so much, have a great day!
By Dave - 7/18/2016

If you prompted your participants to enter the ID themselves, duplicate final digits in the respective phone numbers are the most likely explanation. I frankly don't see any other way, since the numbers are not generated by Inquisit or the launch page in this case.