Strategies to enhance internal validity in multi-center longitudinal research.

Lack of standardized data collection procedures in multi-center longitudinal research poses potential threats to the internal validity of the study. This article addresses several key issues in data collection that can affect the results of longitudinal research. The authors describe these issues in relation to the study currently in progress and cite specific strategies used during data collection to reduce or eliminate data collection inconsistencies. Use of these strategies is not limited to longitudinal, nonexperimental causal models. Outcomes managers and clinical nursing researchers may find some of the strategies useful to enhance the internal consistency of experimental and nonexperimental cross-sectional research.