Introduction to ONYX

ONYX is a free SEM package developed in Germany. We will use it for Assignment 1, a CFA on the Hendrick and Hendrick love styles. ONYX is a graphic-arts-based program (like the commercial product AMOS), so your first experience designing a structural equation model will involve what I hope is an intuitive approach of drawing a picture (before we switch to the more technical, but more broadly applicable, Mplus for later assignments).  Here are some tips I have come up with for using ONYX, given its differences from other SEM programs:

1. Everything is done through right-clicking to bring up menus.

2. You can use an SPSS data file or a plain-text (tab-delimited) ".dat" file saved from an SPSS data file. The ONYX user manual lists available options for designating missing data. Once you've drawn your model, you can use "Load Data" to connect to the .dat file, yielding what's called a "Data Panel."

3. Use the "Create Variable" option to generate either latent or observed variables.

4. You should name latent variables (in ALL CAPITALS) via the right-clicking. However, but you’ll have to drag in the measured variables from the "Data Panel" to the variables' respective boxes in the model. By hovering over the measured-variable boxes, you can verify that the data have been linked.

5. By right-clicking on top of a variable, you can use the "Add Path" tool (the default is to draw unidirectional "causal" paths, whereas holding down the Shift key while using "Add Path" yields dual-headed correlational arrows).

6. All unstandardized factor loadings start out fixed at 1; you should free all of them (i.e., letting them take on freely estimated values). To identify the model (i.e., make sure you're not estimating more quantities than you have information for), construct variances should be fixed to 1.*

7. The default settings yield an unstandardized solution, whereas usually we're interested in a standardized one. You can obtain a standardized solution by right-clicking on each indicator’s box and selecting “z-score Transform.”

8. Covariances (correlations between factors) are also fixed and should be freed.

9. Unlike other programs, which have you submit a "job" or a "run," ONYX is constantly running in the background and responds to changes you make in model specifications. Right-clicking and selecting “Show Estimate Summary” will show current results.

10. The following article provides a concise summary of ONYX, including the claim that its method of seeking a solution is superior to that of other programs (see Figure 6 and the text beginning on the prior page at "Multiple Optima").

von Oertzen, T., Brandmaier, A. M., & Tsang, S. (2015). Structural equation modeling with Ωnyx, Structural Equation Modeling, 22, 148-161. 

*Fixing (or constraining) variables and (under)identification are discussed here.