Transcript Statistical Reasoning

Statistical Reasoning
for everyday life
Intro to Probability and
Statistics
Mr. Spering – Room 113
7.2 Interpreting Correlations

Correlation…
Correlation exists between two variables when higher values
of one variable consistently go with higher values of another
or when higher values of one variable consistently go with
lower values of another.
CHOOSE THE CORRELATION

The number of miles traveled and the amount of gas in your tank.
NEGATIVE
The number of shots taken and the number of shots made.
POSITIVE
The number of hours worked and amount of money earned.
POSITIVE
The breed of dog purchased and age of consumer.
NO CORRELATION
7.2 Interpreting Correlations
Scatter Plots…Scatter Plot is a graph in which
each point corresponds to the values of two
variables…{ not necessarily independent and dependent}
…BEWARE OF OUTLIERS
Outliers can cause “fake” correlations, or mask real
correlations. Always, should examine outliers carefully, they
might tell you something about a relationship that would
otherwise go unnoticed. Also, you should not remove them
unless you have a strong reason to believe that they do not
belong in the data set.
7.2 Interpreting Correlations
Scatter Plots…Scatter Plot is a graph in which
each point corresponds to the values of two
variables…{ not necessarily independent and dependent}
…BEWARE OF INAPPROPRIATE GROUPING
Correlations can be misinterpreted when data are grouped
inappropriately. Sometimes grouping data carelessly can
hide correlations.
What would you expect the correlation to be between hours of
TV watched and High School GPA?
NEGATIVE??? Confounding???
SEE PAGE 301 AND 302: TV and GPA, Tables 7.3, & 7.4
7.2 Interpreting Correlations
• Correlation does not imply causality.
• Possible Explanation for a Correlation
1. The correlation may be a coincidence
2. Both correlation variables might be directly influenced
by some come underlying cause
3. One of the correlated variables may actually be a cause
of the other. Note that even in this case, it may not
necessarily be the cause, but just one of several causes
that work together.
7.2 Interpreting Correlations


HOMEWORK :
pg 304 # 1-19 all