Re: Non-Equivalent Control Groups Design/ Quasi-Experimental Design

Posted by David Marso on Jul 14, 2016; 8:50am
URL: http://spssx-discussion.165.s1.nabble.com/Non-Equivalent-Control-Groups-Design-Quasi-Experimental-Design-tp5732723p5732724.html

You haven't really provided enough information to answer any of these questions.  How for example are "body image" and "weight-loss desire" measured.  VERY IMPORTANT TO KNOW!

"What method should I choose if I want to control the between-group difference before starting any analysis?"  What groups are being compared wrt to what? Between-group difference  in what?  You presumably have heard of random assignment.  Any differences between G1 G2 G3 are obviously not "controllable".  

Re sample size? Good luck on that.  Google Power analysis.  I would suggest consulting with a local statistician or your faculty advisor and experts in the substantive area of research with your measures to get an idea of the general size of mean differences found and the degree of variability within and between groups.

kat92 wrote

Hi,

I would like to know what analysis I should choose to compare the difference between 3 groups. Here's the design:



I have 3 conditions (pictures of either underweight, normal weight, or overweight models, as C1, C2, C3), and I assign the participants to each condition according to their own BMI (G1, G2, G3), so that I will make sure there are at least 9 participants in each combination (e.g. C1G1, C1G2, C1G3, C2G1..., a total of 9 combinations). What statistical test should I use if I want to compare the difference between groups in terms of, say body image and weight-loss desire? What method should I choose if I want to control the between-group difference before starting any analysis?

Since the sample size of each group is around 9, is it also a concern for small sample size for running statistics? How can I know how many participants is enough?

Sorry I have a lot of questions in my mind, but I would be really grateful for your answer.

Thanks,
Kat