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CRIM 430

CRIM 430. Lecture 4: Experimental and Non-Experimental Research. Research Designs. Experimental Design (Classical Experiment) Experimental (receives stimulus) and control groups (does not receive a stimulus)

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CRIM 430

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  1. CRIM 430 Lecture 4: Experimental and Non-Experimental Research

  2. Research Designs • Experimental Design (Classical Experiment) • Experimental (receives stimulus) and control groups (does not receive a stimulus) • Independent variable=experimental stimulus and dependent variable=effect of the stimulus • Pretesting (prior to stimulus) and posttesting (following implementation of the stimulus) • Non-experimental Design • Does not include a comparison group • Contains an independent and dependent variable • May include a stimulus • May not include pre/posttesting

  3. The Classic Experiment

  4. Non-Experimental Research Design

  5. Quasi-Experimental Designs • Classical experiments are not always possible • Quasi-experimental designs provide alternatives to the classical/experimental design • Non-equivalent • Cohort • Time-Series

  6. Quasi-Experimental: Nonequivalent Group Design • Same as experimental designs except groups are not selected randomly • Group placement by convenience • Group placement by first come, first serve • Group placement by matching cases on particular characteristics (e.g., gender, age) • Groups are not considered statistically equivalent; thus, results are subject to bias and inaccuracies • Groups=treatment/experimental group and comparison group

  7. Quasi-Experimental: Cohort Designs • Two different cohorts form the experimental group and comparison group • Only one of the cohorts receives the stimulus • Assumption: Factors influencing creation of one cohort are not significantly different from those influencing a second cohort (within limitations)

  8. Quasi-Experimental: Time-Series Designs • Examine a series of observations on some variable over time • Interrupted time series: Observations compared before and after an intervention is introduced • Can be used with or without a comparison group • Interpretation must be done carefully and after adequate amounts of time and careful consideration of patterns

  9. Validity • Validity is critical to assessing whether a study is strong or weak • Validity=accuracy • Internal validity: • Conclusions drawn from experimental results may not accurately reflect what has occurred in the study—changes are due to another factor

  10. Types of Validity, Cont’d. • Construct validity: • Extent to which the measures we use to measure real-world things are accurate • External validity: • Extent to which research findings in one study apply to other areas (e.g., different cities, populations, etc.)

  11. Threats to Internal Validity • To increase the validity of a study, it is best to use an experimental design • Experimental designs reduce the likelihood that the validity of a study will be threatened • There are twelve primary threats that must be considered when evaluating the quality of a study

  12. 12 Threats to Validity • History: • Historical events that occur during the course of a study and potentially impact study results • Maturation • Change within the subjects that potentially impacts study results • Testing • Potential impact of testing and retesting in and of itself • Instrumentation • Using different measures of the dependent variable at pre-test and post-test • Changes in data collection over time (e.g., record keeping)

  13. 12 Threats, Cont’d. • Statistical Regression • Starting at extreme ends of the spectrum—highly likely that subjects will fluctuate in behavior naturally • Effects erroneously connected to stimulus rather than normal behavior patterns • Selection Biases • Judgmental selection of respondents—e.g., creaming the crop • Experimental Mortality • Subjects drop out of the sample before the study is over • Causal Time Order • Confusion or ambiguity over whether the stimulus came before the dependent variable

  14. 12 Threats, Cont’d. • Diffusion or imitation of treatments • When the treatment and control group subjects are in communication and potentially impact each other’s behavior • Compensatory treatment • When the control group attempts to circumvent what they are being denied (I.e., the stimulus) • Compensatory rivalry • When the control group works harder than they would otherwise to keep pace with the treatment group • Demoralization • Control group subjects give up because they do not have access to the stimulus

  15. Validity and Research Design • Threats to validity can impact all types of research designs • No design is perfect—because human behavior is very complex

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