Leaving aside non-experimental research, quantitative research designs fall into two broad classes: experimental and quasi-experimental. Experimental studies are characterized by the ability to randomize subjects into treatment and control groups. This randomization goes a long way toward controlling for variables which are not included explicitly in the study. Comparison groups in quasi-experimental research are not true randomized control groups as in experimental research. Quasi-experimental research therefore has to control for confounding variables by adding them explicitly in various multivariate statistical techniques which adjust estimates of the relation of causal variables with dependent variables for their correlation with control variables. For this reason, quasi-experimental studies are sometimes called "correlational designs".
Sometimes the term "research design" is equated with the broad study of the scientific method, including aspects of theory construction, hypothesis formation, data collection, and even data analysis. Works on research design by Creswell (2008, 2012), for instance, treat such broad topics as scientific philosophy (ex., pragmatism vs. postpositivism) and methodology of data collection (ex., structured questionnaires versus open-ended interview). To take a second example, Leedy & Ormrod (2009) treat "research design" in terms of building theory, operationalizing definitions, forming hypotheses, using databases, and other phases of the research process. In a third example, for Mitchell & Jolley (2012), "research design" is generating hypotheses, reviewing the literature, operationalizing variables, using descriptive and correlational methods to describe the data, survey research, validity, and experiments.
In contrast to these broader usages of the term, in this volume "research design" is treated under a narrower definition having to do with how measurement should be structured so that effects on the dependent variable may be observed and valid inferences made. While there is some overlap with the broader usages of the term, here research design focuses on the interrelationships among subject selection and grouping, exposure to the dependent variable (treatment in experimental studies), and time of measurement.
For instance, not much can be concluded from one-point-in-time studies of a single group. It is much more informative to have a comparison or control group, and better yet to have measurements before (pretest) and after (posttest) the introduction of the causal variable (the treatment in experimental studies or the change in the causal variable(s) in quasi-experimental studies). It is best of all to have multiple pretests and posttests (time series). These and other considerations of research design are discussed below.
Research design is largely independent of the choice of methods of data collection. Interviewing and survey research, for instance, may be used in experimental, quasi-experimental, and non-experimental research. Similarly, analysis of variance (ANOVA) studies may be experimental or quasi-experimental even though this procedure originated in the experimental research. More on research design may be found in the separate Statistical Associates "Blue Book" volumes on univariate and multivariate GLM (GLM implements analysis of variance). In practical terms, however, some methods of data collection, such as case studies, are used almost exclusively in non-experimental designs.
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Below is the unformatted table of contents.
Table of Contents Overview 6 Key Concepts and Terms 7 Control groups 7 Randomization vs. random sampling 7 Between-subjects vs. within-subjects designs 8 Randomization 8 Between subjects designs 8 Within subjects designs (repeated measures) 9 Matched pairs designs 10 Example comparing between- and within-subjects designs 10 More types of experimental design 11 Factorial designs 11 Full factorial design 11 Fully-crossed vs. incomplete factorial designs 13 Balanced vs. unbalanced designs 13 Completely randomized design 13 Block designs 13 Randomized block designs 13 Latin square designs 14 Graeco-Latin square designs 15 Randomized Complete Block Design (RCBD ANOVA) 15 Split plot designs 17 Mixed design models 18 Pretest-posttest designs 18 Other forms of randomization 19 Lottery designs 19 Waiting list designs 19 Mandated control designs 20 Equivalent time series designs 20 Spatial separation designs 20 Mandated change/unknown solution designs 20 Tie-breaking designs 20 Indifference curve designs 20 New organizations designs 21 Quasi-Experimental Designs 21 Definition 21 One-group posttest-only design 21 Posttest-only design with nonequivalent comparison groups design 22 Posttest-only design with predicted higher-order interactions 22 One-group pretest-posttest design 23 Pretest-posttest design with before-after samples 23 Multiple-group pretest-posttest regression point displacement design 23 Two-group pretest-posttest design using an untreated control group 23 Double or multiple pretest designs 24 Four-group design with pretest-posttest and posttest-only groups 24 Nonequivalent dependent variables pretest-posttest design 24 Removed-treatment pretest-posttest design 25 Repeated-treatment design 25 Switching replications designs 25 Reversed-treatment pretest-posttest nonequivalent comparison groups design 26 Cohort designs with cyclical turnover 26 Interrupted time series designs 26 One-group time series regression-discontinuity design 26 Interrupted time series with a nonequivalent no-treatment comparison group 27 Interrupted time series with nonequivalent dependent variables 28 Interrupted time series with removed treatment 28 Interrupted time series with multiple replications 28 Interrupted time series with switching replications 29 Non-Experimental Designs 29 Definition 29 Examples 29 Frequently Asked Questions 30 Is a quasi-experimental design ever preferable to an experimental design? 30 Is qualitative research a type of quasi-experimental design? 30 How do I handle the problem of sample attrition in designs which involve observations at two or more time periods? 30 Bibliography 31 Pagecount: 34