Sampling Flashcards
What is a population?
all individuals that are there (usually too big to test every individual)
What is a sample?
a smaller group chosen from big group
What is generalization?
applying findings from a sample to a large population
Representative Sample
matches characteristics of the population
Non-Representative Sample
biased
Random sample
identify the population and then draw a random sample from it
Nonrandom sample
choosing special individuals/ subject pools
Only university students
Internet research
Animal subjects (same breed, sex etc.)
Simple Random sampling
randomly selecting a number of people
Stratified sample
dividing population into segments (=strata), then selecting a sample of equal size from each segment
Proportionate Sampling
proportions of people in the population are equal to proportions in your sample
Systematic sampling
every Kth element after a random start
Cluster sampling
naturally occurring groups of subjects and randomly selecting certain clusters
• Multistage sampling: selecting individuals from those clusters
What are characteristics of laboratory research?
• Take individuals into laboratory setting
• Control variables
• More ethical
• High internal validity and low external
validity (discussed next week)
What are characteristics of field research?
• In participants natural environment
• Lesser control of confounding variables
• Results can easily be generalized to the real
world
• High external validity and low internal
validity
Things to consider for research setting (ethics, bias, validity?)
• In participants natural environment
• Lesser control of confounding variables
• Results can easily be generalized to the real
world
• High external validity and low internal
validity
What is internal validity?
- Ability of your research design to adequately test your hypothesis
- Showing that the variation in the independent variable caused the observed effect
What are threats for internal validity?
- Rival hypothesis: another alternative variable might explain the effect
- Confounding: combination of variables explains the effect and one cannot separate the effect of these variables
What are sources of confounding?
• History: specific events other than treatment occur between observations
• Maturation: fatigue or aging change performance over time
• Instrumentation: instrument calibration changes and confounds the effect
• Statistical regression: subjects selected for treatment on the basis of their extreme scores tend to move closer to the mean when retesting
• Biased subject selection: nonrandom
• Experimental mortality: dropouts
• Demand characteristics: participants know
the purpose of the study and behave differently
What is external validity?
• ability of your research design to generalize the results beyond the research setting to real world situations
External vs. Internal validity
- Usually an increase in one means a decrease in other→find compromise
- Theoretical problems: internal
- Real World problems: external
What are threats to external validity?
- Reactive Testing: pretests may affect reaction to the experimental test
- Interactions between participant selection biases and the independent variable: participants that signed up voluntarily could be more extroverted, this could affect your study if you are measuring for example personality types
- Reactive effects of experimental arrangements: artificial experimental setting and knowledge of being a study-participant change results
- Multiple treatment interference: If participants are exposed to multiple treatments and later treatments are affected by former ones
Exam question:
Which of these threaten internal Validity?
I. History
II. Statistical Regression
A. Both I and II are threats.
B. Only I is a threat.
C. Only II is a threat.
D. Both I and II are threats to external validity, but not internal validity.
Answer: A
