Hi Marta -

Thanks for your response. I know it probably seemed self-evident to most on this list, but when one has a client insisting that certain tests be conducted, it gets a bit intimidating. I wanted to be sure I had covered all of the bases, and the collective expertise on this list was definitely the right place to ask! I also received some very helpful suggestions from another person on the list that will provide some answers that at least come close to what is needed.

Thank you again for reading the tome that I posted, and for your corroboration!

Linda

Linda P. Case AutumnGold Consulting (217) 586-4864 www.autumngoldconsulting.com lcase@autumngoldconsulting.com or lcase@uiuc.edu -----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Marta Garcia-Granero Sent: Saturday, July 21, 2007 4:10 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: Selection of Appropriate Tests of Association (long)

Hi Linda

Your impression is correct: you can't obtain any kind of association (correlation, regression) with those two datasets your client gave you. Besides, even if you could (the 21 participants had been obtained from the larger consumer test dataset, with 21 cases you would not be able to get multiple regression models, your sample size should be at least ten times bigger.

Regards, Dr. Marta Garcia-Granero

> Greetings - > > I have a question that may not have an answer, as I am not sure that the > comparisons that are being requested are even possible. On the other hand, > I also fear that I may be missing something very simple and basic! Here is > the problem: > > I have two sets of data. The first is a very large consumer test (CT) that > asked a very large group of participants to evaluate six products after > using them at home. Among many other things, a series of 9 descriptive > questions about each product were included in this study. A 10th relevant > question is an "intent to purchase" query. Each participant assessed one > product. > > The second set of data is a small pilot study of 21 participants. None of > the participants in this small pilot study were tested in the big CT (i.e. > completely different group of people). This is a repeated measures design > in which the same six products are evaluated by each participant and each > product was assessed using three separate assessment tools (i.e. ways of > viewing/interacting with the product). This test took place in a lab, with > no in-home use. The same 9 descriptive questions and the 10th intent to > purchase questions were used to evaluate. > > My client's goal is to assess the degree of association between answers > provided in the small study with those provided for the same products in the > large study. They wish to see how predictive the three assessment tools are > of actual answers after actual use of the product. They asked to start with > simple tests of association (correlation) between each question for each > product using the assessment tools in the small study and the answers to the > same questions from the large CT. The ultimate goal (of the client) is to > conduct either multiple linear regression or logistic regression on the 9 > descriptive questions (IV) to determine their ability to predict the outcome > of the intent to buy question (DV). Of course this would be quite possible > within the big study. However, they are requesting that this is done with > one of the "Assessment tools" used in the small study, NOT with the data > collected from the large CT. In other words, the IVs would come from the > small study and the DV from the large study. I do not see how this is > possible because the participants are not the same in each study (not to > mention the extremely small sample size in the pilot study, but I think that > is a secondary issue, since I do not see how I can run any tests of > association between two unrelated samples). > > My client is first interested in finding out how well the three assessment > tools in the small study agree with answers from the large study. Although > they want correlation, I could think of no way to provide that, so instead > have treated the large data set as "the population" and used aggregate to > create new variables for each question and product that are the mean for > each. I used these as the population mean (seeing that these really do > represent whether or not people would purchase the product after using it), > and have conducted a series of single-sample t-tests for each product and > question against its corresponding "population" mean from the large CT. > These do provide information regarding whether or not the means for each of > the assessment tools differ significantly (or not) from the large CT mean. > This is where I am stuck. I cannot run any type of correlation tests > because the cases (subjects) in each group are completely different people. > My client is very adamant about wanting some test of association. Is there > more that I can do with this design to provide the answers that my client is > requesting? (Again, if I am missing something that is very simple and > obvious, I apologize ahead of time!) > > Thanks for your help in advance (since I know this is long, please feel > welcome to reply off the list if you prefer). > > Linda Case > > Linda P. Case > AutumnGold Consulting > (217) 586-4864 > www.autumngoldconsulting.com > lcase@autumngoldconsulting.com or lcase@uiuc.edu > >