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Experimental Design

Types - Broad Distinction. QualitativeQuantitative. Qualitative Research. NarrativeSubject's own wordsSummarizes behaviorsDescriptiveMethodsInterviewsObservation notesSurveys. Quantitative Research. Numerical data collected

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Experimental Design

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    1. Experimental Design

    2. Types - Broad Distinction Qualitative Quantitative

    3. Qualitative Research Narrative Subject’s own words Summarizes behaviors Descriptive Methods Interviews Observation notes Surveys

    4. Quantitative Research Numerical data collected & analyzed Explores relationship between variables Independent (single or multi-leveled) Dependent (single or multiple) Analysis may permit exploration of an interaction between variable Experimental or quasi-experimental

    5. Experimental Designs Characterized by complete random assignment of groups or subjects Groups are independent Usually employs strong control

    6. Quasi-Experimental Designs Groups or subjects not randomly assigned e.g., sample of convenience May not have a comparison group Typical of clinical research e.g., within subjects repeated measures Less “subject-intensive”

    7. Broad Distinctions Between subjects Dependent measures taken one time Data are independent (i.e., not correlated) Within subjects A “repeated measures” design Dependent measures taken multiple times Data are dependent Mixed Between and within

    8. Design Types Single factor (one-way) Studies one independent variable Multi-factor Studies multiple independent variables May have several levels Examples: Two-way (e.g., 2 x 2) Three-way (e.g., 2 x 2 x 2) Time-series

    9. Single Factor Designs Pretest-posttest (one-group) Pretest-posttest (control group) Posttest-only (control group)

    10. Pretest-Posttest (one group) Quasi-experimental One set of measures taken before and after treatment or intervention Compare pretest and posttest scores Analysis paired t test Weakness No comparison or control group

    11. Pretest-Posttest (control group) Experimental design - random assignment Two groups Control Experimental Measures on dependent variable made on both groups pre- and posttest Significant differences in experimental group not found in control group attributable to treatment Analysis difference scores compared with independent t test ANCOVA pretest score as covariate

    12. Multiple Factor Designs Two-way factorial e.g., 2 x 3 Three-way factorial e.g., 2 x 2 x 3

    13. Two-Way Factorial Design Studies multiple independent variables Main effects (ME) Each with a number of levels (L) Permits study of interactions Analysis ANOVA Example: 2 x 3

    14. Three-Way Factorial Design Studies multiple independent variables Main effects (ME) Multiple levels (L) Interactions effects Analysis ANOVA Post hoc pairwise comparisons Example 2 x 2 x 3

    15. Counterbalanced Design Possibility of order effects biasing data in a repeated measures design Solutions Randomize order Counterbalance trials - order systematically varied Example - two treatments (T1 - T2) “Crossover design” Half of subjects - T1 then T2 Half of subjects - T2 then T1

    16. Latin Square Design Minimizes order effects

    17. Single Subject Design Permits analysis of effects of treatment in individual subjects (or groups) Elements Subjects usually own control Repeated measures Design phases (times series analysis)

    18. Single Subject Design Time series analysis Dependent measure is continuous Establish baseline Measure treatment effect over time

    19. Case Report Subject a single individual Often uses a narrative format May be non-experimental or experimental Develops a profile of the subject using: Visual observation Interviews/surveys/questionnaires Objective data May provide generalizations about other subjects with similar conditions

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