Justin: A couple of random notes.
a. Smoking status (current smoker vs non-current smoker). Including heavy and light smokers in your current smoker group is not double counting. You just have a mixed group of smokers.
b. Smoking status cannot “impact” cognition given that you did not manipulate smoking status. All you have is an attribute variable which may well be confounded with some other variable or variables.
c. I am not sure what you mean by reduce confounding by using a higher number of groups. Using simply current smoker vs. breaking current smoker into two groups of light smoker and heavy smoker is not an issue of confounding. Unless I am missing something.
d. Looking at current smokers (Yes current or No) and processing speed is legitimate given that current smokers is a binary variable. Using only heavier smokers and processing speed does not lend itself to an analysis because you would only have one level of the variable. If on the other hand you meant to say that you had heaver smokers, light smokers and non-smokers than yes you could look for a relation. Or simply heavy smokers vs. nonsmokers-this would work also.
e. In regard for controlling for race if you have a sufficient number of different races (White vs. nonwhite) why not use race a predictor variable and obtain information about the interaction between race and smoking status.
Martin F. Sherman, Ph.D.
Professor of Psychology
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Loyola University Maryland
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From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Justin Blehar
Sent: Sunday, September 30, 2012 12:55 PM
To: [hidden email]
Subject: Re: Controlling for Race with SPSS 20
Pooling some of the groups would work, I'm thinking a combination of descriptive and inferential stats is probably going to be the best course of action. Yes current smokers comprise both the heavy and light smokers so I am double counting cases. A 3 way design may work for this. My intent for the analysis is exploratory to gain a better understanding of how (if at all) smoking status impacts cognition in schizophrenia. The current literature is all over the place with mixed results and various designs. I'm hoping that by using the higher number of groups it can reduce confounds and paint a clearer picture (e.g. they're may be no relation when looking at current smokers and processing speed but a strong relation exists between heavy smokers and processing speed). Ideally I can look at each of these combinations between and within groups. All the while controlling for race.
Cognition is being assessed by: Vocabulary (VC), Matrix Reasoning(MR), Estimated IQ (from VC and MR scores). Ten other individual measures (TMT, BAC, HVLT, WMSlll, LNS, Mazes, BVMT, Fluency, MSCEIT, CPT) and raw scores are converted to T scores and then used to make up 6 cognitive domains plus a total score (Processing Speed, Attention and Vigilance, Working Memory, Verbal Learning, Reasoning Speed, Social Cognition, and a Total Score for the Battery).
Thanks again and I appreciate your patience, I'm new to all of this and really enjoy learning from everyone!
V/R
Justin
From: Art Kendall [[hidden email]]
Sent: Sunday, September 30, 2012 8:31 AM
To: Justin Blehar
Cc: [hidden email]
Subject: Re: [SPSSX-L] Controlling for Race with SPSS 20
Since you have tiny Ns when grouping cases this way, perhaps you should pool some of the groups? Or use and additional IV? with a 3 way design
As is, it looks like you are double counting cases.
E.g., how do you distinguish heavy smokers from current smokers?
Can you put your cases into a 3 way design (3 * 2 *2), degree of exposure, race as IVs and cognition as the DV?
degree of exposure 3 levels: never, light, heavy
current status 2 levels: current/not
race 2 levels: Caucasian, African American.
How are you measuring cognition?
Art KendallSocial Research ConsultantsOn 9/29/2012 8:32 PM, Justin Blehar wrote: