MEASUREMENT

1
MEASUREMENT

• An attempt to provide an objective estimate of a
  natural phenomenon
• e.g. measuring height
• or weight

2
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.

3
Measurement scales Example

• How could you measure height using the following
  levels of measurement?
• Nominal Scales
• Ordinal Scales
• Interval Scales
• Ratio Scales

4
Measurement error

• Evaluate my bathroom scale
• Is it ACCURATE?

5
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.

6
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?
• JUST using the same scale
• Using ANOTHER scale.

7
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.

8
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

9
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

10
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