CHAPTER 6 Control Problems in Experimental Research

Between-Subjects Designs Comparison is between two different groups of subjects (each subject receives one level of IV) Necessary when Subjects in each condition have to be naïve (example: Barbara Helm study (type of crime and attractiveness)) Subject variable (e.g., gender) is the IV Main problem to solve: creating equivalent groups Level 1 Level 2

Creating Equivalent Groups Random assignment Each subject has equal chance of being assigned to any group in the study Spreads potential confounds equally through all groups Accomplished through blocked random assignment

Creating Equivalent Groups Random assignment Each subject has equal chance of being assigned to any group in the study Spreads potential confounds equally through all groups Accomplished through blocked random assignment Matching Deliberate control over a potential confound Use when Small N per group might foil random assignment Some matching variable correlates with DV Measuring the matching variable is feasible

Within-Subjects Designs Also called repeated-measures designs (same subjects in every level of an IV) Comparison is within the same group of subjects Used when comparisons within the same individual are essential (e.g., perception studies) Removes possibility that differences between levels of the IV due to individual differences Level 1 Level 2

Within-Subjects Designs Main problem to solve  order effects Practice effect (progressive) Carry-over (harder to control) Sequence A-B may yield differ carryover than the sequence B-A

Controlling Order Effects RGB RBG BGR BRG GRB GBR Counterbalancing Altering the order of the experimental conditions Complete counterbalancing (all possible orders = x!) Test participants in every possible different order at least once Works well with only a few conditions Partial counterbalancing Random sample of all possible combinations is selected RGBY RGYB RYGB RYBG RBGY RBYG GRBY GRYB GBYR GBRY GYBR GYRB BYRG BYGR BRYG BRGY BGYR BGRY YGBR YGRB YRBG YRGB YBRG YBGR

Methodological Control in Developmental Research Cross-sectional design Longitudinal design Cohort sequential design

Cross-sectional design Methodological Control in Developmental Research: Cross-Sectional Design Cross-sectional design Between-subjects design Participants are arranged in age cohorts Potential for cohort effects Cohort effect: the impact on a study of a group of individuals bonded by age or common experiences Worse with large age differences

Methodological Control in Developmental Research: Longitudinal Design Within-subjects design Participants are re-measured over long spans of time Expensive, time-consuming, likelihood of attrition high In this case, we’d be measuring texting behavior every ten years from when our group is aged 10 all the way to when the same group is aged 80

Cohort-sequential design Methodological Control in Developmental Research: Cohort-sequential Design Cohort-sequential design Both within- and between- subjects design Measure texting of one group at age 60 and 80 Measure texting of a different group at age 40 and 60 Measure texting of a different group at age 20 and 40

Problems with Biasing Experimenter bias/Experimenter Expectancy bias Experimenter expectations can influence subject behavior Controlling for experimenter bias Automating the procedure Using a double blind procedure

Problems with Biasing Subject/Participant bias Hawthorne effect: Effect of knowing one is in a study Evaluation apprehension Participants tend to behave in ideal ways so as not to be evaluated negatively Demand characteristics Cues giving away true purpose and study’s hypothesis Controlling for participant bias Effective deception Field research

Ethical Responsibilities of Participants Be responsible Show up for scheduled appointments, or inform research of cancellation Be cooperative Behave professionally when participating in research Listen carefully Ask questions if unsure of your rights or of what you are asked to do Respect the researcher Do not discuss study with others Be actively involved in debriefing Help the researcher understand your experience