In other words, the same items used in different samples will keep their statistical properties (for instance, difficulty and discrimination), and persons' scores that represent ability or latent traits on a specific construct will not depend on the particular test items they were administered.
We performed a second regression to analyze the effect of instance difficulty on move quality.
We developed a hierarchical logistic regression model to assess the fixed main effects of trial and instance difficulty on move quality.
We controlled for the random effect of participant on the intercept and slope of trial, and the effect on participant on the slope of instance difficulty.
We could not conclude that this was a learned capacity through practice wihtin our study; we even found a negative effect of practice on the cost of solutions, which may well be confounded with the effect of instance difficulty.
Given that the measured effect of eight trials can be approximately compared to the effect of solving a harder instance, it could be concluded that the effect of trials was 5.7 times larger (odds ratio: 2.6/0.45) than increasing the instance difficulty.
For instance, difficulty initiating a task may be due to a reluctance to start, but it could equally well be caused by distractibility/lack of focused attention, or a more general cognitive impairment.
When item parameter estimates are to be used to define competence levels or thresholds for later use, for instance, item difficulties must be highly precise.
For instance, current difficulties of the regional government to create a gastronomy "cluster" could be rooted in the parallel evolution of multiple pre-existing networks: "All the actors are already intricately linked with each other, which makes it very difficult when it comes to creating new forms of cooperation" (interview 2).
For instance, respiratory difficulties, often seen during EVD, might be due to transfusion-related acute lung injury.
It would have been desirable to obtain medical records to verify certain complaints like for instance concentration difficulties and stress whereas other symptoms are more obvious e.g. asthma, hay fewer and eczema.
