PSYC 2250 Lecture Notes - Lecture 8: Repeated Measures Design, Random Assignment, Internal Validity
26 Jun 2018
School
Department
Course
Professor
PSYC 2250 Introduction to Psychological Research
Chapter 8 Experimental Design
Experiments
Used to determine cause-effect under controlled conditions
- E.g. medical research on new drug; clinical research on new therapy
Researchers controls (manipulates) IV to determine DV
Basic logic of Experimental Manipulates:
1. Experimental group manipulate IV Measures DV
2. Control group Measures DV
Notes. Flaws: groups not the same at start of study; other IV’s(3rd variables,
confounds) make cause-effect claims uncertain
Internal validity
When alternative explanations can be ruled out
Achieved via:
- Direct experimental control
- Random assignment
Planning a basic experiment
3 steps:
1. Chose participants and assign to levels of the IV (selection differences)
2. Operationally define IV
3. Operationally define the DV
Different ways of assigning to IV
Depends on the type of design:
- Independent groups design
- Repeated measures design
- Matched-pairs design
Independent groups design (between-subjects design)
Participants randomly assigned to group “equal group”
20-30 subjects minimum per condition is needed
Sometimes…
find more resources at oneclass.com
find more resources at oneclass.com
