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S-005

S-005. Intervention research: True experiments and quasi-experiments. Intervention research. Goal is to assess the effects of some intervention or new idea or approach Examples: Children’s vocabulary growth under a new curriculum Effects of new technologies on student achievement

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S-005

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  1. S-005 Intervention research: True experiments and quasi-experiments

  2. Intervention research • Goal is to assess the effects of some intervention or new idea or approach • Examples: • Children’s vocabulary growth under a new curriculum • Effects of new technologies on student achievement • New approaches to professional development for teachers • New drug treatments or other interventions • Other examples? • Key distinction between • True experiments • We compare the new program (or treatment) to a traditional treatment (or alternative treatment or control group) • Random assignment is the key ingredient for a study to qualify as a true experiment • Quasi-experiments • Comparison of new program with an alternative (“new” vs. “traditional”, for example) • But random assignment not used • Comparisons may be biased by other factors • Need for great care and additional information for these studies to be convincing • Quasi-experimental designs are common in education, but they may have some important limitations. (Some describe them as “mere observations” and not a strong basis for drawing conclusions. Others are not quite so harsh.)

  3. True Experiments (for evaluating an intervention) Control (or traditional or alternative) New treatment Comparison New

  4. True Experiments (for evaluating an intervention) Control (or traditional or alternative) New treatment Start with a group of eligible people Key issue: How do people get assigned to (or chosen for) the two options? Comparison New Assign them randomly

  5. True Experiments (for evaluating an intervention) Control (or traditional or alternative) New treatment Start with a group of eligible people Key issue: How do people get assigned to (or chosen for) the two options? Comparison New Assign them randomly Random assignment is the key ingredient required for a true experiment.

  6. True experiments(for assessing an intervention) The process of random assignment Comparison New Makes it very likely that the groups will be similar. The only difference will be which treatment they receive. The groups are very likely to be similar in age, gender ratio, prior experience, etc. Some cautions: Compliance? Implementation? Sometimes the special conditions under which we carry out a true experiment make it hard to generalize. Others?

  7. Quasi-experiments • Groups are compared, but no random assignment ? Do we really have a good comparison? Can we really be sure about the new program? Comparison New Often we need lots of additional information to help us draw stronger conclusions?

  8. Quasi-experiments What might we conclude?

  9. Quasi-experimentsTwo scenarios

  10. Quasi-experimentsAn even better scenario

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