LESSON 2 - PSYCHOLOGY AS A SCIENCE (PART 2)

DESCRIPTIVE STATISTICS

Describe, organize, and summarize data

FREQUENCY STATISTICS

# of times a specific data point appears

MEASURES OF CENTRAL TENDENCY

• Mean (average)

• Median (midpoint)

• Mode (most common)

NEGATIVELY SKEWED

Tail is found in the beginning

SYMMETRIC SKEWED

Tails are found on the same ends

POSITIVELY SKEWED

Tail is found in the end

SKEW

Name for its tail

MEASURES OF VARIABILITY

Ways of describing how far scores are spread from the mean

STANDARD DEVIATION

A numeric indicator of how far the scores are spread from the mean

FAR SPREAD

A lot of people are scoring way above and below the mean = high standard deviation

CLOSE SPREAD

Few people are scoring away from mean/scores are clustered around the mean = low standard deviation

INFERENTIAL STATISTICS

Results that are from smaller groups to make predictions of larger groups

SAMPLE VS POPULATION =

Subset vs All

CORRELATION

The relationship between two variables

CORRELATION COEFFICIENT

The numeric indicator of that relationship

POSITIVE CORRELATION

Both variables change in the same direction (whether that’s an increase or decrease)

NEGATIVE/INVERSE CORRELATION

Both variables change in opposite directions

STRENGTH

The closer to absolute 1, the stronger the correlation; the closer to zero, the weaker

0 - |1.2|

Weak

|.3| - |.5/.6|

Moderate

>|.6|

Strong

P-VALUE

The probability our result is due to chance (is the result statistically significant)

p < .05

LESS than 5 times in 100 in our results are due to chance = statistical significance

p > .05

MORE than 5 times in 100 our results are due to chance = non-significant