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国外心理学研究方法课件12.variables
Reliability & Validity Sampling error
Measuring your dependent variables
Errors in measurement Sampling error
Population
Everybody that the research is targeted to be about
Reliability
Test-restest reliability
Test the same participants more than once • Measurement from the same person at two different times • Should be consistent across different administrations Reliable Unreliable
Control variables Random variables
Confound variables
Many kinds of Variables
Scales of measurement Errors in measurement
Reliability & Validity Sampling error
Selecting every nth person
Systematic sampling
Step 1: Identify groups (clusters) Step 2: randomly select from each group
Cluster sampling
Use the participants who are easy to get
Experimenter bias & reactivity History – an event happens the experiment Maturation – participants get older (and other changes) Selection – nonrandom selection may lead to biases Mortality (attrition) – participants drop out or can’t continue Regression to the mean – extreme performance is often followed by performance closer to the mean
Measuring your dependent variables
Example: Measuring intelligence?
How do we measure the construct? How good is our measure? How does it compare to other measures of the construct? Is it a self-consistent measure?
Control variables Random variables
Confound variables
Many kinds of Variables
Independent variables (explanatory) Dependent variables (response) Extraneous variables
Setting representativeness
Ecological validity - are the properties of the research setting similar to those outside the lab
External Validity
Scales of measurement Errors in measurement
“This guy seems smart to me, and he got a high score on my IQ measure.”
Face Validity
Usually requires multiple studies, a large body of evidence that supports the claim that the measure really tests the construct
• Are the raters consistent?
Requires some training in judgment 5:00 4:56
Reliability
Does your measure really measure what it is supposed to measure?
There are many “kinds” of validity
Construct Validity
The precision of the results
Did the change in the DV result from the changes in the IV or does it come from something else?
Internal Validity
The SI cover jinx
Threats to internal validity
Are experiments “real life” behavioral situations, or does the process of control put too much limitation on the “way things really work?”
Estimate of true score biased
unreliable invalid
reliable invalid
reliable valid
Dartboard analogy
True score + measurement error
A reliable measure will have a small amount of error Multiple “kinds” of reliability
Susceptible to biased selection
Sampling Methods
Every individual has a equal and independent chance of being selected from the population
Simple random sampling
Sample
Allows us to quantify the Sampling error
Sampling
Goals of “good” sampling:
– Maximize Representativeness:
– To what extent do the characteristics of those in the sample reflect those in the population
Sample
The subset of the population that actually participates in the research
Sampling
Population Sampling to make data collection manageable Inferential statistics used to generalize back
– Reduce Bias:
– A systematic difference between those in the sample and those in the population
Key tool: Random selection
Sampling
Probability sampling
Validity
VALIDITY
CONSTRUCT INTERNAL EXTERNAL
FACE
CRITERIONORIENTED
PREDICTIVE CONCURRENT
CONVERGENT DISCRIMINANT
Many kinds of Validity
VALIDITY
CONSTRUCT INTERNAL EXTERNAL
External Validity
Variable representativeness
Relevant variables for the behavior studied along which the sample may vary
Subject representativeness
Characteristics of sample and target population along these relevant variables
Simple random sampling Systematic sampling Stratified sampling
Have some element of random selection
Non-probability sampling
Convenience sampling Quota sampling
Reliability
Internal consistency reliability
Multiple items testing the same construct Extent to which scores on the items of a measure correlate with each other • Cronbach’s alpha (α) • Split-half reliability