Descriptive Statistics

Question 1

Central tendency

Answer 1

Summarizes where data is clustered around

Mean, median, mode

Question 2

Mode

Answer 2

Most frequently occurring value (best for categorical data; only choice for nominal data)

Question 3

Median

Answer 3

Middle value when data are sorted

Used mainly for numeric data that is skewed

Question 4

Mean

Answer 4

Average of values

Only for numeric data that isn’t skewed

Question 5

Variance

Answer 5

Explains for entire spread of data how far it is from the mean
s^2
Reason for squaring: further penalizes for being far away from mean and further rewards for being close to the mean

Question 6

Standard deviation

Answer 6

s (square root of variance)

Question 7

Empirical rule for normally distributed data

Answer 7

68% of data lie within 1 standard deviation of mean
95% of data lie within 2 standard deviations of mean
99.7% of data lie within 3 standard deviations of mean

Question 8

Z score

Answer 8

(value - mean)/ standard deviation

Measures how far value is from the mean (how many standard deviations)

Question 9

5 number summary for box plots

Answer 9

Minimum (lower whisker), Q1 (first part of box to line), median (line), Q3 (line to end of box), maximum (higher whisker)

Question 10

Q1

Answer 10

Bottom 25% of data

Question 11

Q3

Answer 11

Top 25% of data

Question 12

Interquartile range

Answer 12

IQR= Q3 - Q1

Middle 50% of data

Question 13

IQR method

Answer 13

Outliers: behind Q1 - 1.5(IQR) or beyond Q3 + 1.5(IQR)