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An attempt to provide an objective
estimate of a natural phenomenon
◦ e.g. measuring height
◦ or weight
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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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
How could you measure height using the
following levels of measurement?
◦ Nominal Scales
◦ Ordinal Scales
◦ Interval Scales
◦ Ratio Scales
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Evaluate my bathroom scale:
Is it ACCURATE?
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
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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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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• 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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• 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 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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