Running experiment at two sites - match computers and refresh rates?

[Scott]

Keeping in mind David's initial assessment, that concerns depend on the 
study paradigms and research questions, I think we also need to ask whether 
the two labs both use CRT or LCD monitors. If the latter, it might be more 
important to use the same monitors than the same computers. Sorry if I'm 
opening a can of worms, but admit I'm fishing for advice about this myself.

On Thursday, November 15, 2012 3:35:56 PM UTC-6, McFarlane, David wrote:
>
> Mary Kate, 
>
> Good question, I hope others weigh in.  Here are my thoughts. 
>
> Obviously, the more uniform the better.  So one might turn the 
> question around and ask how much nonuniformity is too much.  And that 
> will depend largely on the timing demands of the study, some studies 
> have more stringent requirements than others. 
>
> Offhand, I would say that as long as each of your computer setups can 
> robustly deliver millisecond-quality times, you should be OK.  You 
> can and should test each one with the RefreshClockTest that you can 
> download from PST, see Chapter 3 of the original User's Guide, or 
> Chapter 4 of the revised version.  Bear in mind that RefreshClockTest 
> just tests whether the system can keep up with the onboard 
> millisecond clock, it does not test the accuracy of the clock per se, 
> for that you would need to compare times with an external time 
> standard.  In any case, you at least want all your machines to pass 
> RefreshClockTest. 
>
> Matching refresh rates again depends on your timing requirements.  To 
> take an example, If you have one display running at 60 Hz (refresh 
> period = 16.7 ms) and another at 75 Hz (refresh period = 13.3 ms), 
> and you ask for a Duration of 200 ms, then the one display will 
> actually give you either 183 or 200 ms, while the other screen will 
> give you either 199 ms or 213 ms.  You will have to decide whether 
> that is acceptable.  Note that the production release (EP2.0.10.242) 
> allows you to request a refresh rate 
> (http://www.pstnet.com/support/kb.asp?TopicID=3465 ).  No guarantee 
> that you will get what you ask, so still look at the value measured 
> by E-Prime & reported in the .edat file.  (And go with the value 
> measured by E-Prime, do not trust the refresh rate reported by Windows.) 
>
> I do not have any particular refresh rate to recommend, I do not run 
> studies myself (I am a Systems Designer who helps others do their 
> research), and I am embarrassed to say that I have never asked others 
> what refresh rates they use, I will have to ask around.  Offhand it 
> seems that faster is better as you get more exact times.  OTOH, I 
> often tend toward lowest common denominators for greater 
> compatibility, and for that reason might stick down at 60 Hz.  In 
> truth, rightly or wrongly, I think we mostly just take whatever 
> refresh rate we get and don't think about it. 
>
> You already plan to use the same size monitors at all sites, and I 
> presume use the same display resolution.  I trust you will also seat 
> subjects at the same distance so that visual stimuli subtend the same 
> visual angle for all subjects. 
>
> Note that none of this affects the accuracy of response times, 
> E-Prime has a very robust mechanism for gettting responses which is 
> independent of the mechansims for presenting stimuli. 
>
> Now after all that, here is the short answer (Michiel, would like to 
> chime in here?):  Chances are that whatever human behavior you 
> measure has more variance than your measurement system.  That's not 
> an excuse for getting sloppy when you can be exact, but maybe we need 
> not fret too much about this; others have done statistical 
> calculations to show that we can compensate for variance introduced 
> by our measuring system merely by running a few more subjects (sorry, 
> I don't have a citation handy). 
>
> So what do the rest of you think?  For that matter, what do others 
> actually do? 
>
> ----- 
> David McFarlane 
> E-Prime training 
> online:  http://psychology.msu.edu/Workshops_Courses/eprime.aspx 
> Twitter:  @EPrimeMaster (https://twitter.com/EPrimeMaster) 
>
>
> At 11/15/2012 12:28 PM Thursday, MKT wrote: 
> >We will soon be running the same experiment on E-Prime 2.0 at two 
> >sites (OSU and UPenn). We want to make sure we do not add any 
> >additional noise in the data or run into problems. 
> > 
> >We plan to use the same size monitors at both sites and run on 
> >Windows 7. Is it necessary to match computer type as well? How about 
> >refresh rates? Is there a particular refresh rate you recommend? 
> > 
> >Thanks for your help! 
>
>

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