Moreover, a non-weighted prognostic model (sum score) was constructed, whereby HR and Kaplan Meier curves with 0 to 3 risk factors were assessed.
In the Rasch model, simple sum scores can be used to easily determine a person's ability level (see Boone and Scantlebury, 2006).
Thus, also under the IRT model, analysing sum scores leads to an underestimation of shared environmental effects and an overestimation of dominance genetic effects when the sum score distributions are skewed.
For some estimation problems, it might be computationally more convenient to model sum and differences scores, instead of the latent scores for the twins separately (Van den Berg et al. 2006a; Robert and Casella 2004, p. 396; cf. Boomsma and Molenaar 1986).
For the CTT model, the sum score defined in equation Eq. 3 is considered to be an unbiased estimate of the true score.
On the basis of this six-factor model, a sum score, which is easy to use in clinical practice, was created as an estimation of the risk of developing moderate or severe persistent pain in the operated area.
A model based on sum scores did not suffer from these restrictions but introduced larger prediction errors.
> -wrap-foot> aFull Model: adjusted for age, sex, clinical indication for chest CT, image quality and type of medical centre bDue to the limited number of stroke events, no cases occurred in the highest TAC category for the ascending aorta and consequently no hazard ratio could be calculated We also calculated multivariate-adjusted models with TAC and CAC sum scores entered simultaneously.
The TICS authors found a nine-factor model based on the item values and a two-factor model based on the sum scores of the nine scales [ 17].
For the genetic modeling the log-transformed sum scores were analyzed only in subjects who had at most two missing items.
