Descriptive Statistics

Question 1

What are descriptive statistics?

Answer 1

Describe the data you have

Question 2

What is the population?

Answer 2

Entire group of people you are interested in

Question 3

What is a sample?

Answer 3

Subset of population

Usually represented with n (also known as sample size)

Question 4

What is categorical data?

Answer 4

Usually nominal or ordinal

Two or more categories with no ordering to them

Question 5

What are examples of categorical data?

Answer 5

Hair colour

Marital status

Question 6

What is discrete data?

Answer 6

Usually ordinal, ratio or interval variables

Fixed value with logical order

Question 7

What are examples of discrete data?

Answer 7

Shoe size

Score out of 10

Question 8

What is continuous data?

Answer 8

Usually ratio or interval variables

Can take any fractional value

Question 9

What are examples of continuous data?

Answer 9

Reaction times

Question 10

How can categorical data be presented in a frequency distribution?

Answer 10

As its raw frequency or as a percentage frequency

Question 11

How can discrete data be presented in a frequency distribution?

Answer 11

As raw frequency or percentage

As cumulative frequency or percentage

If loads of values, use frequency ranges instead (grouped in meaningful way)

Question 12

What are measures of central tendency?

Answer 12

Sometimes want to condense entire frequency distribution into single number

Where might want to calculate tendency of data

Question 13

What are three types of measures of central tendency?

Answer 13

Mode

Median

Mean

Question 14

What is the mode?

Answer 14

Score occurring most often in dataset

Sometimes takes more than one value (bimodal and multimodal distributions)

Question 15

What data is the mode used for?

Answer 15

Nominal data

Question 16

What is the median?

Answer 16

Middle score in dataset

Middle value in dataset or mean of middle two values

Question 17

How do you work out the median for odd value datasets?

Answer 17

(n+1) / 2

Question 18

How do you work out the median for even value datasets?

Answer 18

(middle two values) / 2

Question 19

What are the pros of the median?

Answer 19

Insensitive to outliers

Often gives real, meaningful data value

Question 20

What data is the median used for?

Answer 20

Ordinal data

Skewed interval/ratio data

Question 21

What are the cons of the median?

Answer 21

Ignores a lot of data

Difficult to calculate without a computer

Can’t use with nominal data

Question 22

What is the mean?

Answer 22

Sum of data points divided by number of data points

Question 23

What are the pros of the mean?

Answer 23

Uses all of the data

Most effective for normally distribution datasets

Question 24

What are the cons of the mean?

Answer 24

Sensitive to outliers

Values not always meaningful

Only meaningful for ratio and interval data

Question 25

What measure of spread is used for the mode?

Answer 25

None

Question 26

What measure of spread is used for the median?

Answer 26

"Distance based" measures Range, IQR

Question 27

What measures of spread are used for the mean?

Answer 27

"Centre-based" measures Variance, standard deviation

Question 28

What is the interquartile range?

Answer 28

Similar to range but ignores most extreme values Range of scores within middle 50% of scores UQ - LQ

Question 29

What is the lower quartile?

Answer 29

Median of lower half of data

Question 30

What is the upper quartile?

Answer 30

Median of upper half of data

Question 31

What are the pros of the IQR?

Answer 31

Insensitive to outliers Often gives real, meaningful data value Useful for ordinal data and skewed interval/ratio data

Question 32

What are the cons of the IQR?

Answer 32

Ignores lot of data Difficult to calculate without a computer Can't use with nominal data

Question 33

What is the deviance?

Answer 33

Each score subtracted from mean Could see deviance of "0" How far score is away from the mean

Question 34

What is the sum of squared errors (SS)?

Answer 34

Deviance is squared and all deviances are summed More data points = bigger SS

Question 35

What is the variance?

Answer 35

"Average" of sum of squared errors

Question 36

What are the pros of the variance?

Answer 36

Uses all data Forms basis of several other tests/statistics

Question 37

What are the cons of the variance?

Answer 37

Requires normal distribution Sensitive to outliers Units not sensitive

Question 38

What is the standard deviation?

Answer 38

Measure of spread that's equal to the unit of measurement of DV Square root of the variance Can measure s of population or an estimated s of population based on sample Allows us to get unbiased estimate of population's s if only have access to sample of data