Sampling and Measurement

1
Sampling and Measurement

• Psychological Research Methods

2
Sampling

• Goal
• Measure subset of population
• Obtain reliable and valid estimate
• Generalize back to population

3
Types of Sampling

• Probability Sampling
• Random
• Physical Mixing Process
• Random Numbers Table
• Stratified Random

4
Random Numbers Table
25484 32654 22101 24578 45478 98753 41211 87010
32847 77651 54125 65688 55412 26895 35212
xxx

• Assign every member of the population a number
• The number of digits for each number should
  accommodate the number of people in the
  population
• Randomly select a starting point on the table

5
Somewhere between Probability and Non-Probability
Sampling(Trochim, 2005)

• Cluster Sampling
• Randomly sample from preexisting clusters
• Systematic Sampling
• Every nth individual

6
Non-Probability Sampling

• Haphazard
• Purposive
• Modal Instance
• Expert
• Quota
• Heterogeneity
• Snowball

7
Assignment to Groups

• Random Assignment
• Systematic Assignment

8
Measurement Reliability

• Definition
• Measurement Error
• Random
• Systematic

• Types
• Inter-rater
• Test-retest
• Parallel Forms
• Internal consistency
• Inter-item
• Average Item-Total
• Split-Half
• Cronbachs Alpha

9
Measurement Validity

• Definition
• For a Study
• Internal
• External

• For a Measure
• Construct
• Face
• Content
• Criterion-Related
• Predictive
• Concurrent
• Convergent
• Discriminant

10
Levels (Scales) of Measurement

• Levels
• Nominal
• Ordinal
• Interval
• Ratio
• Relationship to Statistics