• Quasi-experimental studies do not allow the researcher to assign participants to experimental conditions.
  
  
• Two common quasi-experimental designs are factorial designs with nonmanipulated variables and interrupted time-series designs.
  
  
• Single-subject designs have advantages of focus, flexibility, and not leaving participants untreated in control groups. They also are limited when effect sizes are small and multiple variables cannot be studied.
  
  
• Naturalistic observation works best when we are unobtrusive, have identified the behaviors we need to observe in advance, and raters are blind to study hypotheses.
  
  
• Meta-analyses allow us to combine effects across many different studies.

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