POLI 110 Lecture 12: Poli 110 (Mar 5)

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8 Feb 2016
Measurement Error
Poor validity or reliability  measurement error
Two kinds of measurement error
- Bias (systematic error)
oError produced when our measurement procedure
produces scores that are, on average, either too high or too
low relative to the truth
oUpward bias vs. downward bias
oMay also be too high or too low for everyone or just for
certain subgroups
oNot the same as political or ideological bias
Concept: Exposure to political advertising
A possible Measure: ask people the following question:
How many campaign advertisements have you seen in the last
Measurement Error
- Random Error
oError that derives from random features of the
measurement process or the phenomenon
oOn average, random error cancels out over lots of
iterations (but bias does not)
- Looking speci2c source for discrepancy
Random Error
Source of random error
- Imperfect memory (for survey/interview measures)
- Variability in top-of=mind considerations
- Calculation/counting errors (eg., national statistics)
- Sampling error
Random error
- Random error cancel out over lots of iterations, so to minimize
random error you can:
oRepeat measures for lots of cases/individuals
oRepeat measure for some case at many points in time
- The full set of cases (countries, individuals, wars, etc) that we’re
interested in learning about
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