Vocabulary
Quantitative measure of how spread-out or clustered scores are
Variability
What are some factors that can affect variability?
Extreme scores, open-ended distributions, sample size
σ 2 = SS/N
Population variance
In a distribution of z- scores the mean is always ___ and the standard deviation is always ___.
0 and 1
Distance between largest and smallest score
Range
What measure of variability is reported with the median?
Semi-Interquartile Range
What measure of variability is reported with the mean?
Standard deviation and variance
S2= SS/n-1
Sample Variance
What happens to the shape, mean, and standard deviation of the z- distribution?
Shape stays the same, mean is always 0, and standard deviation is always 1.
True/False
Z-scores that are above the mean are always positive
True
Number of scores free to vary?
Degrees of freedom
Variability describes distribution in terms of ?
distance
How do you find standard deviation?
Square root of the variance
Every raw score has a corresponding z-score
True
True or false
The population uses degrees of freedom in an attempt to get unbiased.
False
sample
Distance between first and third quartile
Interquartile
What is a disadvantage of the range?
Provides an incomplete picture of variability
n-1
degrees of freedom
If our treatment is ______, then we have evidence that the treatment had an _______?
noticeably different, effect
Quartile 2 (Q2) is also know as
50th percentile
Each individual in the population has an equal chance of being selected.
Random Sampling
Measure of variability should be
Stable and reliable
x= μ + z σ
and
(x- μ) / σ
Raw score formula and Z score formula
What information can a z score give?
Provides an objective method for determining how well a sample represents a population
True/False
Z-scores that are below the mean are always negative
False