Twin Multivariate Dataset Simulation

S. Purcell
This module is designed to
  • to calculate the correlation matrices resulting from a cholesky decomposition specification of multivariate twin data
  • to simulate datasets with properties specified as above
The Cholesky is specified as shown below (in this case for 3 variables). That is, for n observed variables, the columns represent latent variables (where the ith latent variable acts on the ith to the nth observed variables) and the rows represent the observed variables.
          LV 1   LV 2   LV 3
 Trait 1  p11    
 Trait 2  p12    p22
 Trait 3  p13    p23    p33

3 variables multivariate
4 variables multivariate
The simulation option produces either a page of data in comma-separated value format or space-delimited format with no headers. Either save (as text only, not as source html) or cut-and-paste into your favourite text-editor and save from there. The space-delimited format is more convenient for directly simulating data for analysis in Mx, which prefers datasets with no non-numerical symbols.

The dataset is formatted as follows :

 ID  Zyg  Twin1Trait1  Twin2Trait1 ... ... Twin1TraitN Twin2TraitN 
Please note that this is not how data would usually be read into Mx. Therefore, in your script the label command should read
      Labels id zyg x1 x2 y1 y2
in the case of a bivariate analysis, where x and y are the variables for twins 1 and 2, but the select command should read
      Select x1 y1 x2 y2

Last updated 20.05.2007 by Shaun Purcell