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Hi,
I have encountered several problems in doing bivariate SEM models, which is an important part of my graduation project.The main problems are as follows:
1. Could I put a tri-categorised but not ordinal variable and a binary variable into the bivariate SEM model? e.g. smoking status (0-never smokers,1-former smokers, 2-current smokers) and abdominal obesity (0-WHtR≤0.5, 1-WHtR>0.5). I didn't know whether the non-ordinal variable was accepted, so I converted "smoking status" into 3 binary variables that reflected smoking initiation (0-never smokers, 1-former or current smokers), current smoking (0-never or former smokers, current smokers) and smoking persistence (0-former smokers, 1-current smokers).
2. For current smoking and abdominal obesity (both binary traits), ACE model had lower AIC than AE and CE models, and the difference of model fitting between ACE and AE or CE was statistically significant (P-value<0.05).However, the phenotypic correlation (rp) was only 0.04, common environmental correlation (rc) was 0.102, and the special environmental correlation (re) was -0.143, of which the direction is opposite of rp and rc, I didn't know how to explain this situation.
3. Based on the results above, I wanted to calculate bivariate h2, c2 and e2, but I was not sure about the right calcualtion formula (See Figure1). And if the pathway coefficient such as a11 was not significant (95%CI included zero), was it still necessary to put the estimate of a11 into the formula in Figure1.
4. After adjusting for age (continuous variable) in the bivariate model above, results were different from above. Especially, I found a negative bivariate h2 and e2, and I didn't know how to explain this situation? (See Figure2)
5. On top of that, I wanted to know if saturated model can output tetrachoric correlations?
I'm looking forward to your help, thanks!
Cheeres,
Yaning