5. Bias Flashcards
What are two types of graphs used for detecting outliers?
- Scatterplots (less helpful with several predictors)
- Histograms
In an average sample, 95% of standardised residuals should lie between…
+-2 SD
In an average sample, 95% of standardised residuals should lie between…
+-2.5SD
Any case for which the absolute value of the standardised residual is 3 or more, is likely to be…
An outlier
What does Cook’s distance measure?
Measures the influence of a single case on the model as a whole
In Cook’s distance, values greater than __ may be cause for concern
1
DF beta statistics tell us…
The change in b when a case is removed
With DF beta statistics, be wary of standardised values with absolute values…
> 1
The population model should have what two errors?
- Homoscedastic errors
- Independent errors
The relationship between predictor(s) and outcome is…
Linear
The combined effect of predictors is…
Additive
A model’s errors refer to what?
The differences between predicted values and observed values of the outcome variable in the population model
These values cannot be observed
A model’s residuals refer to what?
The differences between predicted values and observed values of the outcome variable in the sample model
These values can be observed and are representative of the population model errors
What does “Errors should be independent” mean?
The population error in prediction for one case should not be related to the error in prediction for another case
What does “errors should be homoscedastic” mean?
Variance of population errors (residuals) should be consistent at different values of the predictor variable
