Descriptive Statistics: Measures of Variability

Question 1

measures of variability

Answer 1

numbers which describe how “spread out” a set of data is

Question 2

what are the measures of variability?

Answer 2

range (interquartile range), deviation, variance, standard deviation

Question 3

range

Answer 3

length of the smallest interval that contains all the data

=largest value-smallest value

Question 4

range is sensitive to:

Answer 4

artificial sample size, if small samples, the range is smaller, extreme scores

Question 5

interquartile range (IQR)

Answer 5

measure of distance between the first and third quartiles, which are the splitting points that contain 50% of the middle scores
=(Q3-Q1)

Question 6

how to calculate interquartile range:

Answer 6

1. find median

2. find quartile location (half of median)

Question 7

outliers

Answer 7

extreme values that don’t fit with the rest of the data

Question 8

how to determine if points are outlier:

Answer 8

if score is greater than (Q3 + (1.5IQR)), then it is a high end outlier
if scores is smaller than (Q1+(1.5IQR)), then it is a low end outlier

Question 9

deviation

Answer 9

the difference between each score and the mean of the data set (find mean score and calculate deviation for each entry

Question 10

variance

Answer 10

single number representing the average amount of variation in a set of scores = s^2

Question 11

standard deviation

Answer 11

measure of the spread of scores out from the mean of the sample, the most common way of describing spread of values = s, the square root of variance

Question 12

to interpret standard deviation:

Answer 12

use the empirical rule (68-95-99.7 Rule)

Question 13

how to use the Empirical Rule:

Answer 13

only use if data has normal distribution:

• 68% of data lies within 1SD of mean
• 95% of data lies within 2SD of mean
• 99.7% of data lies within 3SD of mean