MEASUREMENT
• An attempt to provide an objective
estimate of a natural phenomenon
– e.g. measuring height
– or weight
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Measurement scales
• Nominal Scales
– Categories -- mutually exclusive and collectively exclusive.
• Ordinal Scales
– Rank order – e.g. most important to least important.
• Interval Scales
– Ordinal + the intervals between data points are equal.
• Ratio Scales
– Above + a meaningful absolute zero or origin.
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Measurement scales: Example
• How could you measure height using
the following levels of measurement?
– Nominal Scales
– Ordinal Scales
– Interval Scales
– Ratio Scales
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Measurement error
Evaluate my bathroom scale:
Is it ACCURATE?
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Reliability
• Consistent results over time.
• Measures are free from random error.
Test-Retest Reliability:
Obtained by repeating the measurement
using the same instrument under as
nearly the same conditions as possible.
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Validity
Addresses the issue of whether what we
tried to measure was actually measured.
How do I know if my bathroom scale is
valid?
That is, does 160 really MEAN anything?
How could I know this with my bathroom scale?
1. JUST using the same scale
2. Using ANOTHER scale.
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Types of Validity
• Face validity
• Content validity
• Criterion-Related Validity
• Predictive Validity
• Concurrent Validity
• Construct Validity
• Convergent Validity
• Discriminant Validity
All types of validity are related.
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Reliability and Validity Illustrated
• Situation 1:
• A lack of reliability
• my scale varies a lot (150, 160, 170)
• Situation 2:
• High reliability, but lacks validity
• My scale always shows 160, but other scales are
different
• Situation 3:
• Reliable, consistent, and valid
• ALL scales show a consistent 160
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Scaling
Scaling Defined
In order to decrease noise:
you measure something several times
• Unidimensional scaling
• Multidimensional scaling
• Graphic Rating Scales
Present to respondents with a graphic continuum
typically anchored by two extremes
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Types of scales
Rank Order Scale
Judging items against others
Chevy, Ford, Chrysler…
Paired Comparisons
Picking one item (repeated for all items)
Chevy or Ford? Ford or Chrysler? Chevy or Chrysler?
The Semantic Differential
The researcher selects opposite pairs
e.g., hate… love
Likert Scales
Express either a favorable or unfavorable attitude
1 “strongly disagree” to 7 “strongly agree”
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The End
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