Variability

Question 1

Deviation

Answer 1

distance between a raw score and the mean

population:
deviation = X - μ

sample:
deviation = X - x̄

Question 2

Sum of squares

Answer 2

statistical measure of deviation from the mean

square the distance between each raw score and the mean, then add them together
(∑X)2 / N

dividing SS by the sample size N gives the variance

Question 3

Variance

Answer 3

expresses the “average” squared deviation from the mean
unsquared = standard deviation

population:
σ2 = SS/N

sample:
s2 = SS/N-1

Question 4

Standard deviation

Answer 4

measure of how dispersed the data is in relation to the mean
ie, low sd –> scores are clustered around mean
high sd –> scores are spread out

s = √ SS / N-1

population:
σ = √σ2

sample:
s = √s2

Question 5

Normal curve

Answer 5

theoretical distribution of population scores

Question 6

Normal curve distribution

Answer 6

Question 7

z-score

Answer 7

how many standard deviations above or below the mean a raw score is