Averages And Measures Of Spread

Question 1

What is a median

Answer 1

Middle observation in set of ordered data

Question 2

What is a mode

Answer 2

Most frequently occurring numbers

Question 3

How do you calculate the median

Answer 3

N+1 divided by 2

This number along in the list

Question 4

What is a positive and negative skew

Answer 4

Positive = curve peaks left of the middle

Positive = mean greater that median

Question 5

What is a normal distribution

Answer 5

Mean and median approx equal

Question 6

What should you do if both variables are categorical

Answer 6

Use a contingency table

Question 7

What is a percentile

Answer 7

Value at or below which a specified percentage of the scores in the distribution fall

Question 8

How do you calculate percentiles

Answer 8

Percentile / 100

X n+1

(N is number of digits in data set)

This answer, this number in array

Question 9

What is a quintile

Answer 9

5 equal groups that the population can be divided into (20%s)

Question 10

What is a tertile

Answer 10

Thirds

Question 11

What is the range

Answer 11

Difference between highest and lowest values

Question 12

What is the interquartile range

Answer 12

Difference between upper and lower quartile

Question 13

What is the sd

Answer 13

Measures average deviation from the mean

Question 14

What is variance

Answer 14

SD squared

Question 15

What is a box plot

Answer 15

Graph of median, inter quartile range and outliers

Question 16

When is SD used

Answer 16

When the mean is a good measure of average

Question 17

What do larger/ smaller SDs mean

Answer 17

Larger - more spread from mean

Question 18

When is sd used

Answer 18

When the data is not too skewed or when mean is being used as measure of average

Question 19

What is a residual

Answer 19

Difference between particular observation and the mean

Question 20

What happens if we add or subtract by a constant number in a data set

Answer 20

Changes the mean by the amount added or subtracted

SD remains the same

Question 21

What is the variance

Answer 21

Standard deviation squared

Question 22

What happens when you multiply or divide by a constant

Answer 22

Changes mean by an amount equal to multiplying or dividing by the mean

Does the same to SD

Question 23

What happens to range if distribution when you multiply or divide by a constant

Answer 23

Shrink if less than 1, decreased range

Increase if constant more than 1, increased range

Question 24

What is it called when the observations have been converted into z scores

Answer 24

Standardised data

Question 25

What is the z score equation

Answer 25

Z = observation - mean / SD

Question 26

What do positive and negative z scores mean

Answer 26

Positive = above the mean
Negative = below the mean

Question 27

What does a Z score measure

Answer 27

The number of standard deviations an observation is from the mean

Question 28

What does the mean of the z scores always equal

Answer 28

0

Question 29

What does the sd of all the z scores always equal

Answer 29

1

Question 30

What are z scores used for

Answer 30

To rank data

Can create ranking scales on several variables

Can then compare z scores for these indicators by creating an index of all variables