A.P. Psychology Statistics Notes

Correlation

The way 2 factors vary together and how well one predicts the other

Positive Correlation- direct relationship where factors increase or decrease together

Negative Correlation – Inverse relationship where one factor goes up while one goes down

Continued…

Illusory Correlation

-perceiving correlation when none exists

-we notice random coincidences as not random, rather as correlated

Statistical Reasoning

Mode – the most frequently occurring score in a distribution

Mean – the arithmetic average of a distribution

Median – the middle score in a distribution

Measures of Variation

Range – the difference between the highest and lowest scores in a distribution

Standard Deviation – A computed measure of how much scores vary around the mean score

Statistical Significance – A statistical statement of how likely it is that an obtained result occurred by chance

68-95-99.7 Rule

In practice, one often assumes that the data are from an approximately normally distributed population.

If that assumption is justified, then about:– 68% of the values are within 1 standard deviation of

the mean

– about 95% of the values are within two standard deviations

– and about 99.7% lie within 3 standard deviations.

68-95-99.7 Rule

Skew

A distribution is skewed if one of its tails is longer than the other. – Positive Skew - long tail in the positive direction.

– Negative Skew - long tail in the negative direction.

– No Skew – symmetric, normal distribution.

Distributions with positive skew are sometimes called "skewed to the right" whereas distributions with negative skew are called "skewed to the left."

Positive Skew

Negative Skew

No Skew (Normal Distribution)