Thanks Paul. I've downloaded G*Power. Question: the correlational component of the study revealed r = -.21, p<04 (higher tendency to humanize nature were associated with a lower tendency to help victims of a natural disaster). The next test will be an independent samples t-test.
How does this info help me enter the values needed by G*Power: "Effect Size d" and "Allocation ratio N2/N1"? Michael Michael A. Britt, Ph.D. [email protected] http://www.ThePsychFiles.com Twitter: @mbritt On Aug 27, 2013, at 8:41 AM, Paul C Bernhardt <[email protected]> wrote: > > > > > > > There is software to determine this. One excellent and free app is G*Power. > > http://www.psycho.uni-duesseldorf.de/abteilungen/aap/gpower3/ > > I would use the correlational study to give me an estimate of effect size. As > you describe, I would use that in the software to estimate my number of > participants to attain the desired power. Practicality constraints on number > of available participants usually limits things. I did such an estimate using > G*Power a few weeks ago for a study we are planning. We will need to collect > data over two semesters because the anticipated number of participants > available from one semester's worth of students would only give us power of > about .66, whereas two semester's worth would bump us up over .90. > > Paul > > On Aug 27, 2013, at 8:18 AM, Michael Britt wrote: > >> >> >> >> >> >> >> I'm reading an interesting piece of research on anthropomorphism which >> essentially states after a natural disaster if we use the term "mother >> nature" when describing it, people will be less willing to contribute to >> relief efforts ("Humanizing nature could help the perceiver to conceive >> natural events as imbued with intentionality and significance rather than >> considering them merely random and meaningless phenomena"). They did two >> studies. Here's the issue/question: >> >> Study 1 was correlational and involved 96 students. The results were >> supportive at <.001 >> Study 2 was an experiment (no need to go into the details) involving 56 >> students. The results were, in the authors words, "tangentially" supportive >> with p<.06 >> >> I think the study was well conducted so I don't mean to slight the >> researchers. My guess is that if they used more subjects they probably >> would have reached p<.05 - but would that have been an example of "selective >> stopping"? I assume it would be. >> >> So how exactly does a researcher determine beforehand - as we are suggesting >> they do - the number of subjects they ought to try to get for the study? >> I'm just not familiar with the process. Does one look at the effect sizes >> of previous related studies to determine if the effect is large or small and >> then make a decision? But let's say the effect is assumed to be small, so >> do you use 100 subjects? 500? How is this number determined? >> >> Appreciate the insight in this. >> >> Michael >> >> Michael A. Britt, Ph.D. >> [email protected] >> http://www.ThePsychFiles.com >> Twitter: @mbritt >> >> >> --- >> >> You are currently subscribed to tips as: [email protected]. >> >> To unsubscribe click here: >> http://fsulist.frostburg.edu/u?id=13441.4e79e96ebb5671bdb50111f18f263003&n=T&l=tips&o=27372 >> >> (It may be necessary to cut and paste the above URL if the line is broken) >> >> or send a blank email to >> leave-27372-13441.4e79e96ebb5671bdb50111f18f263...@fsulist.frostburg.edu >> >> >> >> >> > > > --- > > You are currently subscribed to tips as: [email protected]. > > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=13405.0125141592fa9ededc665c55d9958f69&n=T&l=tips&o=27373 > > (It may be necessary to cut and paste the above URL if the line is broken) > > or send a blank email to > leave-27373-13405.0125141592fa9ededc665c55d9958...@fsulist.frostburg.edu > > > > > --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=27377 or send a blank email to leave-27377-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
