PSY1022 Lecture Notes - Lecture 8: Internal Validity, Repeated Measures Design, Time Control
26 May 2018
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PSY1022 – Lecture – Week 8
- experimental and quasi experimental design
- cause and effect involved
- experimental research
• involves systematically manipulating an independent variable to examine
its effects on a dependent variable - whilst controlling/limiting
extraneous variable so that a cause and effect relationship between the IV
and DV can be established
• goal of experimental research is explanation - establish a cause and effect
relationship
• to achieve this goal it is necessary to
•
o manipulate one independent variable to create two or more
treatment conditions
o measure a DV
o compare the DV scores for each condition
o control all extraneous variables
- quasi experimental research
• weaker level of en=vidence
• attempts to achieve the same goal as the experimental strategy but
without random assignment
• quad independent variable is indirectly manipulated to examine its effects
on a dependent variable
• as in experiments - quasi experimental studies should have
•
o cause precedes effect
o the cause and effect covary
o alternative explanations for the causal relationship are
implausible
• examines differences between two or more groups of scores
- non experimental research
• this involves examining/describing the relationship between two
variables without explaining the relationship
• can be used for production
• cross sectional design
•
o often used in developmental research
o looks at several group of people at one point in time
o advantages
o
▪ les time consuming and expensive than longitudinal
studies
▪ less participant attrition
▪ may have better external validity - generalisation
o disadvantages
o
▪ individual changes not asses
▪ can be cohort or generation effects
▪ worse internal validity - cause and effect
find more resources at oneclass.com
find more resources at oneclass.com
- longitudinal design
• the same group of individual are assessed at different points in time
• advantages
•
o individuals come from a common background, hence no cohort
effects
o can assess individual changes
• disadvantages
•
o expensive and time consuming
o participant attrition can be high and create bias
- correlational research strategy
• description of variables
•
- internal and external validity
• refers to the entire research study - not just the measurement procedures
•
o validity refers to how well the study addresses the research
question
• each research strategy has its own set of pros and cons - best explained in
the internal and external validity of the research study
- internal validity
• if a research study is able to show that changes in independent variable
lead to changes in dependent variable - no other alternative variable
could be responsible for these changes - high internal validity
• threats to internal validity
•
o ambiguos temporal ordering
find more resources at oneclass.com
find more resources at oneclass.com
