Item parameter estimates vary for a variety of reasons, including estimation error, characteristics of the examinee samples, and context effects (e.g., item location effects, section location effects, etc.). Although we expect variation based on theory, there is reason to believe that observed variation in item parameter estimates exceeds what theory would predict. This study examined both items that were administered linearly in a fixed order each time that they were used and items that had appeared in different adaptive testing item pools. The study looked at both the magnitude of variation in the item parameter estimates and the impact of this variation in the estimation of test-taker scores. The results showed that the linearly administered items exhibited remarkably small variation in parameter estimates over repeated calibrations. Similar findings with adaptively administered items in another high stakes testing program were also found when initial adaptively based item parameter estimates were compared with estimates from repeated use. The results of this study also indicated that context effects played a more significant role in adaptive item parameters when the comparisons were made to the parameters that were initially obtained from linear paper-and-pencil testing.