Transcript Correlation vs. Causation

Statistics 101
Measures of Central Tendency
• Mean
-
Average
• Median -
Middle
• Mode
Most Common
-
How many cookies did you eat last week?
22
6
Mean
100
15
18
1
30
6
22+6+100+15+18+1+30+6+6 = 204
204/9 = 22.66
Median 1 6 6 6 15 18 22 30 100
Mode 1 - one instance
6 - three instances
15 - one instance
18 - one instance
22 - one instance
30 - one instance
6
The Normal Curve
• Standard Deviation
• Variation from the mean (or another point)
• % of scores in a distribution that fall
above/below a given score.
Standard Deviation
To calculate the Variance, take each difference, square it, and then average the result
And the Standard Deviation is just the square root of Variance, so:
Standard Deviation lets us know
what’s normal or average.
Scatterplots
Perfect positive
correlation (+1.00)
Scatterplot is a graph that comprises of points
generated by values of two variables.
The slope of points depicts the direction,
The amount of scatter shows the strength of
relationship.
Scatterplots
Perfect negative
correlation (-1.00)
No relationship (0.00)
Scatterplot on the left shows a relation between the
variables, and the one on the right shows no relationship
between the two variables.
Correlation Coefficient
Value of r
Strength of Relationship
-1.0 to -0.5 or 1.0 to 0.5
STRONG
-0.5 to –0.3 or 0.3 to 0.5
Moderate
-0.3 to –0.1 or 0.1 to 0.3
Weak
–0.1 to 0.1
None or very weak
Percentile Rank