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Measurement Error. Rating Sheet. 1 Manage time effectively. 2 Manage resources effectively. 3 Scan a multitude of information and decide what is important. 1 2 3 4 5. 4 Decide how to manage multiple tasks. 5 Organize the work when directions are not specific. 1 2 3 4 5. 1 2 3 4 5.
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Rating Sheet 1 Manage time effectively 2 Manage resources effectively. 3 Scan a multitude of information and decide what is important. 1 2 3 4 5 4 Decide how to manage multiple tasks. 5 Organize the work when directions are not specific. 1 2 3 4 5 1 2 3 4 5 3 Scan a multitude of information and decide what is important. 1 Manage time effectively 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 True Score Theory Observed score True ability Random error + = X e + T
The Error Component X e + T Two components:
The Error Component X e + T Two components: er
The Error Component X e + T Two components: er • Random error
The Error Component X e + T Two components: er • Random error es
The Error Component X e + T Two components: er • Random error es • Systematic error
The Revised True Score Model X er es + + T
What Is Random Error? • Any factors that randomly affect measurement of the variable across the sample. • For instance, each person’s mood can inflate or deflate performance on any occasion. • Random error adds variability to the data but does not affect average performance for the group.
Random Error Frequency The distribution of X with no random error X
Random Error The distribution of X with random error Frequency The distribution of X with no random error X
Random Error The distribution of X with random error Frequency The distribution of X with no random error Notice that random error doesn’t affect the average, only the variability around the average. X
Any factors that systematically affect measurement of the variable across the sample. • Systematic error = bias. • For instance, asking questions that start “do you agree with right-wing fascists that...” will tend to yield a systematic lower agreement rate. • Systematic error does affect average performance for the group.
Systematic Error Frequency The distribution of X with no systematic error X
Systematic Error The distribution of X with systematic error Frequency The distribution of X with no systematic error X
Systematic Error The distribution of X with systematic error Frequency The distribution of X with no systematic error Notice that systematic error does affect the average; we call this a bias. X
Reducing Measurement Error • Pilot test your instruments -- get feedback from respondents. • Train your interviewers or observers • Make observation/measurement as unobtrusive as possible. • Double-check your data. • Triangulate across several measures that might have different biases.
