RM8 Correlation

What is correlation?

an association between 2 measures

What does correlation show?

the strength of an association

• not a slope

What is effect size?

strength of a relationship between 2 variables

What is statistical significance?

chance of obtaining the finding if no effect exists

• the chance a finding is real rather than being a coincidence

What are the 3 warnings about correlations?

1) curvilinear relationships

2) Outliers

3) Restricted Range

What is a curvlinear relationship?

pearson r=0, but there may still be a relationship that just isn’t linear

• curve, linear then plateaus, etc.

What is an outlier?

a data point that is outside of a correlated set and affects data

When are outliers more significant?

smaller data sets are far more affected by outliers

What is restricted range?

strength of correlation may shrink if either measure is reduced

what is an example of reduced range?

childs grade level v knowledge of geography.

• they dont start learning until 4th grade so itd be pretty flat up until 3

Correlation does not prove causation. Why?

A third variable may be present

What is a spurious variable?

a correlation due to a third variable or coincidence?

What is an example of a spurious variable?

ice cream sales and shark attacks went up. Hot weather is the third variable, those are not connected at all