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Sample Size Estimation for Longitudinal Designs with Attrition: Comparing Time-Related Contrasts Between Two Groups

Author

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  • Donald Hedeker
  • Robert D. Gibbons
  • Christine Waternaux

Abstract

Formulas for estimating sample sizes are presented to provide specified levels of power for tests of significance from a longitudinal design allowing for subject attrition. These formulas are derived for a comparison of two groups in terms of single degree-of-freedom contrasts of population means across the study timepoints. Contrasts of this type can often capture the main and interaction effects in a two-group repeated measures design. For example, a two-group comparison of either an average across time or a specific trend across time (e.g., linear or quadratic) can be considered. Since longitudinal data with attrition are often analyzed using an unbalanced repeated measures model (with a structured variance-covariance matrix for the repeated measures) or a random-effects model for incomplete longitudinal data, the variance-covariance matrix of the repeated measures is allowed to assume a variety of forms. Tables are presented listing sample size determinations assuming compound symmetry, a first-order autoregressive structure, and a non-stationary random-effects structure. Examples are provided to illustrate use of the formulas, and a computer program implementing the procedure is available from the first author.

Suggested Citation

  • Donald Hedeker & Robert D. Gibbons & Christine Waternaux, 1999. "Sample Size Estimation for Longitudinal Designs with Attrition: Comparing Time-Related Contrasts Between Two Groups," Journal of Educational and Behavioral Statistics, , vol. 24(1), pages 70-93, March.
    • Handle: RePEc:sae:jedbes:v:24:y:1999:i:1:p:70-93
    DOI: 10.3102/10769986024001070
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    Cited by:

    1. Satoshi Usami, 2017. "Generalized SAMPLE SIZE Determination Formulas for Investigating Contextual Effects by a Three-Level Random Intercept Model," Psychometrika, Springer;The Psychometric Society, vol. 82(1), pages 133-157, March.
    2. Mathieu Bunel, 2012. "Évaluer un dispositif sectoriel d'aide à l'emploi : l'exemple des hôtels, cafés et restaurants de 2004 à 2009," Economics Working Paper Archive (University of Rennes & University of Caen) 201223, Center for Research in Economics and Management (CREM), University of Rennes, University of Caen and CNRS.
    3. Mathieu Bunel & Yannick L'Horty, 2011. "Les effets des aides publiques aux Hôtels Cafés Restaurants et leurs interactions," Working Papers halshs-00658460, HAL.
    4. Anindya Roy & Dulal K. Bhaumik & Subhash Aryal & Robert D. Gibbons, 2007. "Sample Size Determination for Hierarchical Longitudinal Designs with Differential Attrition Rates," Biometrics, The International Biometric Society, vol. 63(3), pages 699-707, September.
    5. Narayan Sastry & Bonnie Ghosh-Dastidar & John Adams & Anne R. Pebley, 2003. "The Design of Multilevel Survey of Children, Families, and Communities: The Los Angeles Family and Neighborhood Survey," Working Papers 03-21, RAND Corporation.
    6. Mathieu Bunel & Yannick L'Horty, 2011. "Les effets des aides publiques aux Hôtels Cafés Restaurants et leurs interactions : Une évaluation sur micro-données d'entreprises," Working Papers halshs-00744905, HAL.

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