PSY403 Between-subjects and Within-Subjects Design PDF

Experimental Designs: Between-subjects design Within-subjects design Mariana V. C. Coutinho, PhD Outline • Research Strategies • Research Designs • Experimental Design • Between-subjects design • Within-subjects design What Is a Research Strategy? Refers to the general approach and goals of a r...

Experimental Designs: Between-subjects design Within-subjects design Mariana V. C. Coutinho, PhD Outline • Research Strategies • Research Designs • Experimental Design • Between-subjects design • Within-subjects design What Is a Research Strategy? Refers to the general approach and goals of a research study • Descriptive Research Strategy • Correlational Research Strategy • Experimental Research Strategy: Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. What Is a Research Strategy? Refers to the general approach and goals of a research study • Descriptive Research Strategy: describes individual variables (rather than a relationship between variables) • Correlational Research Strategy: examines the relationship between variables, whether changes in one variable is accompanied by changes in another. • Experimental Research Strategy: examines cause and effect relationships between variables. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Research Designs • It is about how we will implement the research strategy. • Require decisions about three basic aspects of the research study: 1. Same individuals versus different individuals 2. The number of variables to be included • A research design is a general framework for conducting a study. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Two Basic Experimental Research Designs • Between-subjects design • Within-subjects design Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Question • You will be presented with the structure of both between and within subject designs, and you need to decide which is which. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. What are the main differences between the two designs? • Between-subjects design • Within-subjects design Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. What are the main differences between the two designs? • Between-subjects design: includes two or more groups of participants and each group is tested in only one treatment and control conditions. • Within-subjects design: includes a single group of participants and each individual is tested in all of the different treatment and control conditions. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. What are the main differences between the two designs? • Between-subjects design – Only one score is obtained for each participant. • Within-subjects design – Two or more scores are obtained from each participant. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. What are the main differences between the two designs? • Between-subjects design – Each set of scores is obtained from different groups of participants. • Within-subjects design – Different sets of scores are obtained from the same group of participants. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1 5 4 3 5 4 7 6 7 8 7 4 9 8 7 8 9 6 7 6 7 8 7 4 1 5 4 3 5 4 9 8 7 8 9 6 Two Basic Experimental Research Designs • Within-subjects design 1. Two or more scores are obtained from each participant. 2. Study repeats measurements of the same individuals under different conditions 3. Often called a repeated-measures design Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Advantages of Between-Subjects Designs • Each individual score is independent from all other scores. • The individual’s score is not influenced by: – practice or experience gained in other treatments – fatigue or boredom from participating in a series of different treatments Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Disadvantages of Between-Subjects Designs • Require a relatively large number of participants – Example: three different treatment conditions with 30 scores in each treatment ► 90 participants are required • Each score is obtained from a unique individual who has personal characteristics different from all of the other participants. – Individual differences Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Effects of Individual Differences in Groups • The groups in a between-subjects experiment must be as similar as possible except for the IV distinguishing them. – If the groups are different, then individual differences can become confounding variables. ▪ It then becomes impossible to draw conclusions about a treatment. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Age as a Confounding Variable Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Additional Confounding Variables • Two major sources of confounding in between-subjects designs: – Confounding from individual differences ▪ Example: participants in one group may be older, smarter, taller, or have higher socioeconomic status than the participants in another group. – Confounding from environmental variables ▪ Example: testing one group in a large room and another group in a smaller group. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Advantages of Within-Subjects Design • A within-subjects design: – The group in one treatment is exactly the same as the group in every other treatment. – No individual differences between groups to confound the study ▪ Each subject appears in every treatment condition. ▪ Each subject serves as their own control. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Disadvantages of Within-Subjects Designs • Each participant goes through a series of treatment conditions. • Practice and fatigue can influence the results. Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Research Procedures • Details about how the study is to be done – Exact, step-by-step description of a specific research study • Includes a determination of: – Exactly how the variables will be manipulated, regulated, and measured – Exactly how many individuals will be involved – Exactly how the individual participants will proceed through the course of the study Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Thank you! Gravetter | Forzano, Research Methods Behavioral Sciences, 6th Edition. © 2023 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.