Within item response theory, the latent trait (e.g., ability) is often depicted as $\theta$. Within item response theory, I have also come across the term $\theta$-grid. For example, the description of the tam.latreg function within R's TAM package package states that "only the individual likelihood evaluated at a $\theta$-grid is needed as the input" (p. 103).

I tried to find more information on what the $\theta$-grid is but to no avail. I wonder if it is comparable to thresholds within categorical factor analysis, which divide the continuous range of a latent factor into different subsets. Accordingly, the number of thresholds are a function of the number of options within the categorical items. However, this does not seem to be the case in the case of $\theta$-grids. What is a $\theta$-grid?

  • 1
    $\begingroup$ Could you provide a reference? $\endgroup$
    – Ryan Volpi
    Jun 21, 2022 at 1:48
  • $\begingroup$ @RyanVolpi, I added an example where I came across the term. Thanks $\endgroup$
    – DomB
    Jun 21, 2022 at 8:29

1 Answer 1


The term $\theta$-grid or grid is used throughout the entire manual of TAM. Even so, I didn't find any point in the manual where the term was defined. The term, however, refers to the Gauss-Hermite quadrature points that are employed in TAM for numerical approximation of the integral over the ability distribution.

The term grid is used also by Adams, Wilson and Wang (1997, p. 5), one of the main references for TAM.


Adams, R. J., Wilson, M. and Wang, W.-C. (1997). "The Multidimensional Random Coefficients Multinomial Logit Model." Applied Psychological Measurement 21(1): 1-23.


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