Threats to PPMCC (Factors affecting
correlation):
1.
Outliers:
the data that stands out in the scatterplot does not contribute to the
relationship and must be omitted. (for small group outlier has large effects).
Outliers does not go with the linear relationship (must have performed poor in
exam 3 and outstanding in exam 4). Value of r will increase if the outliers
are removed and more accurate
depiction of the relationship between the predictor and the outcome measures because outliers
are the threats to the PPMCC and results decrease in r value. So, on removing
outliers data shows better liner relationship thus increase in r value.
2.
Combined groups: Two
groups separately may not show any relationship individually but together may
show a strong relationship.
3.
Extreme groups: There
is no relationship (r = 0) between
two variables for low performing groups
and high performing groups individually, but together they show the
relationship.
4.
Range restriction (truncated range): If we restrict the range (means accept only high SAT
scorers we will not be able to see the relationship on how low SAT scores are
going to do in college so) relationship is going to be lower. Truncated range
lowers the correlation.
5.
Nonlinear relationship (curvilinear
relationship): is not explained by PPMCC.
No comments:
Post a Comment