Millisecond Forums

Great to hear everything seems to be working now. Thanks for letting me know and thanks for sharing your SPSS syntax with others as well.

And thanks again Dave, much appreciated. The support you guys offer is top notch. 

Ah yes when I first saw the stuff about the modulo arithmetic, I didn't really know how that could be used to generate appropriate group numbers, but that makes complete sense to me now and is all working. I have my spss syntax recoding those sometimes 6 figure group numbers into my three groups that can be used for analysis. 

COMPUTE group_code=MOD(group-1, 3) +1.
EXECUTE.

group_code is the new variable generated that is either 1, 2, or 3. 

Oh, and I should add that you can also set your web experiment to generate group ids *sequentially* in case you're more comfortable with that. That amounts to pretty much the same thing your PHP script is intended to achieve.

The group number will be random, not constrained to values 1, 2 and 3. That, however, does not matter. See:

https://www.millisecond.com/forums/Topic13856.aspx

In short, your script takes the random number modulo n (where n is the number of conditions as in "1 of 3") to determine which of the n conditions to assign. Simple modulo arithmetic. 1 mod 3 = 1 -> 1st condition. 2 mod 3 = 2 -> 2nd condition. 3 mod 3 = 0 -> 3rd condition. 4 mod 3 = 1 -> 1st condition... 12887 mod 3 = 2 -> 2nd condition.

And yes, three <batch> elements would have worked as well, but seems entirely unnecessary (unless I'm missing something).

Oh on the contrary, I'm sure it is I that is missing something ;) 

If I do that, it will select 1 of 3 groups will it with no replacement? I thought random was properly random, as in no way (on first glance) to specify a random number between an integer (in this case between 1 and 3) ? 

Yes that would be much easier if that is all there is to it. 

Just out of interest though, something like the code I sent before would also work to achieve the same thing?

I don't see why you would even need three <batch> elements and three versions of manipulationweb.iqx. Why can't you just leave everything as is and just set your launch page to generate a random groupid instead of retrieving it from a query parameter?

I'm sure I'm missing something here, but I don't know what.

Yeah the trouble is, the IT guy in our department set this php up so I don't have access at the mo.

> Hmm, that's actually the default option, so I'm not sure why you think this isn't possible. 

So am I right in thinking that if I just randomised the participant number and had the following for my batch file, would this achieve the randomisation I need? Would this split people into three roughly equal groups without the link?

Bare in mind the only difference in the experiment is the manipulationweb iqx.

<batch one>
/ subjects = (1 of 3)
/ groupassignment = groupnumber
/ file = "Consentformweb.iqx"
/ file = "manipulationweb_1.iqx"
/ file = "Questionsweb.iqx"
/ file = "Debriefweb.iqx"
</batch>

<batch two>
/ subjects = (2 of 3)
/ groupassignment = groupnumber
/ file = "Consentformweb.iqx"
/ file = "manipulationweb_2.iqx"
/ file = "Questionsweb.iqx"
/ file = "Debriefweb.iqx"
</batch>

<batch three>
/ subjects = (3 of 3)
/ groupassignment = groupnumber
/ file = "Consentformweb.iqx"
/ file = "manipulationweb_3.iqx"
/ file = "Questionsweb.iqx"
/ file = "Debriefweb.iqx"
</batch>

> What I do wish was that there was a way to select groups randomly with no-replacement as you might the participant number.                                

Hmm, that's actually the default option, so I'm not sure why you think this isn't possible.

Regarding your PHP redirection script: You have access to the server that hosts and runs the script. The server's logs should tell you exactly which IPs accessed it and the URL it redirected any given IP to (including the respective query parameter value). You can match those records with the logs available in your millisecond account. That should tell you which values your PHP script gave out and whether they correspond to the condition administered by Inquisit / the value of the group number. The server logs should also tell you whether the PHP script is giving out values as you intended it to or not.

Let me know what you find there.

> "after clicking start, this pops up: Inquisit was unable to contact the server to verify that this script is licensed. The script will not > be run."

This means one of two things:

(1) TLS is disabled on the participant's box. To fix that, have her/him go to

Internet Options -> Advanced -> Security -> Check 'Use TLS 1.0'

(and any higher TLS versions). Previous protocol versions (SSLv2 and v3) are no longer supported by the server (they are insecure).

(2) A firewall or the like (either local or on the network perimeter) is blocking traffic between the Inquisit engine on the client and the server.