Experimental Design Designs that allow testing of hypotheses
Learning objectives • Describe pre-experimental, experimental and quasi-experimental research designs. • Explain the types of conclusions you can draw from data obtained in at least three different types of research designs described. • Read a research article and describe the research design • Describe the research design for your research project.
Non-experimental Designs • Qualitative – construct meaning • Descriptive – quantitative descriptive stats • identifying characteristics of an observed phenomenon or exploring possible associations among two or ore phenomena. • Examines a situation as it is • Correlations • Surveys, questionnaires, structured interviews, checklists • NO causality
Demonstrating causality • Variables • Independent • Dependent • Experimental Designs • Experimental • Quasi-experimental • Post Facto Designs
Pre Experimental • Does not show cause & effect • Independent “variable” does not vary • Experimental/control groups not equivalent or randomly selected • Usefulness: Forming tentative hypotheses more controlled studies
Pre-Experimental • One-shot experimental case study • One Group Pre/Post test • Static Group Comparison Time
True Experimental • Random assignment of subjects causality • Pre/Post test Control Group • Solomon Four-Group Design - • Does the pre-test impact the post test?
True Experimental - 2 • Posttest Only Control Group • Within Subjects Design – • i.e. one exam (Obs), • Tx1 – some content taught with case studies, some content taught by pure lecture
Quasi-Experimental Designs • Randomized subjects impossible or not practical • Don’t control for all confounding variables - need to account for them in discussion • Nonrandomized Control Group Pre/post • See others on table
Ex-Post facto • After the fact • Results do not allow causality conclusions • i.e. study of students who have failed a course once and are retaking it.
What is the study design? • A researcher studies the effects of two different kinds of note-taking training (one of which is placebo) on the kinds of notes that college students take. Her sample consists of students enrolled in two sections of an undergraduate course in educational psychology; with the flip of a coin, she randomly determines which section will be the treatment group and which will be the control group. She analyzes the content of students’ class notes both before and after the training, making the prediction that the two groups’ notes will be similar before the training but qualitatively different after the training. • Quasi-experimental: Nonrandomized control group pre/post test (Design 8)
What is the study design? • Hoskins, et. al. article • Darland and Carmichael article
Conclusions • Even with control groups, not all research designs allow you to draw conclusions about causality. • Pick a research design that allows you to make the types of conclusions about the data that you are interested in making.