title: Quasi-experimental study designs series-paper 9: collecting data from quasi-experimental studies.
abstract: OBJECTIVE
  To identify variables that must be coded when synthesizing primary studies that use quasi-experimental designs.
  
  
  METHODS
  All quasi-experimental (QE) designs.
  
  
  RESULTS
  When designing a systematic review of QE studies, potential sources of heterogeneity-both theory-based and methodological-must be identified. We outline key components of inclusion criteria for syntheses of quasi-experimental studies. We provide recommendations for coding content-relevant and methodological variables and outlined the distinction between bivariate effect sizes and partial (i.e., adjusted) effect sizes. Designs used and controls used are viewed as of greatest importance. Potential sources of bias and confounding are also addressed.
  
  
  CONCLUSIONS
  Careful consideration must be given to inclusion criteria and the coding of theoretical and methodological variables during the design phase of a synthesis of quasi-experimental studies. The success of the meta-regression analysis relies on the data available to the meta-analyst. Omission of critical moderator variables (i.e., effect modifiers) will undermine the conclusions of a meta-analysis.
authors.affiliation: Educational Measurement and Statistics, 368 Lindquist Center, University of Iowa, Iowa City, IA 52242, USA. Electronic address: ariel-aloe@uiowa.edu.
authors.forename: Ariel M
authors.initials: AM
authors.lastname: Aloe
authors.affiliation: College of Education, Florida State University, 3210D Stone Building, Tallahassee, FL 32306-4453, USA.
authors.forename: Betsy Jane
authors.initials: BJ
authors.lastname: Becker
authors.affiliation: School of International Development, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Maren
authors.initials: M
authors.lastname: Duvendack
authors.affiliation: Department of Counseling and Human Development, University of Louisville, 309 Porter Education Building, Louisville, KY 40292, USA.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Valentine
authors.affiliation: EPPI-Centre, University College London, 10 Woburn Square, London WC1H 0NR, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Shemilt
authors.affiliation: International Initiative for Impact Evaluation (3ie), 36 Gordon Square, London WC1H 0PD, UK.
authors.forename: Hugh
authors.initials: H
authors.lastname: Waddington
mesh_terms: D003625:Data Collection / Q000379:methods*; D017408:Guidelines as Topic; D006801:Humans; D065228:Non-Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*; D012107:Research Design
keywords: Bivariate effect size; Effect modifiers; Meta-analysis; Moderator variables; Partial effect size; Quasi-experiment