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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

CRIM 430

Lecture 4: Experimental and Non-Experimental Research

research designs
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
quasi experimental designs
Quasi-Experimental Designs
  • Classical experiments are not always possible
  • Quasi-experimental designs provide alternatives to the classical/experimental design
    • Non-equivalent
    • Cohort
    • Time-Series
quasi experimental nonequivalent group design
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
quasi experimental cohort designs
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)
quasi experimental time series designs
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
  • 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
types of validity cont d
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.)
threats to internal validity
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 threats to validity
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)
12 threats cont d
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
12 threats cont d1
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
validity and research design
Validity and Research Design
  • Threats to validity can impact all types of research designs
  • No design is perfect—because human behavior is very complex