Descriptive Statistics

Question 1

What is a histogram?

Answer 1

A diagram with rectangles whose area is proportional to the frequency of a variable and whos consist of bins (x-axis) and its y-axis is the frequency (number of observations).

Question 2

What are descriptive statistics?

Answer 2

A visual descriptor of a data set.

Question 3

What are inferential statistics?

Answer 3

Using your data to infer something about the general population

Making predictions about a broader set of people, situations or events

Question 4

What is the R command for histograms?

Answer 4

hist()

Question 5

What is the mean?

Answer 5

The average of the results of the data.

Question 6

How do you calculate the mean?

Answer 6

Add up each of the data points and divide by the number of data points total (N)

Question 7

What is the median?

Answer 7

The middle observation

Question 8

What is the mode?

Answer 8

The most frequently observed value in the data

Question 9

What are the measures of central tendency?

Answer 9

Mean

Median

Mode

Question 10

What are the measures of spread?

Answer 10

Range

Interquartile Range

Standard Deviation

Question 11

What is the range?

Answer 11

The full range of values in the data set.

(0%-100%)

Question 12

How do you calculate the range?

Answer 12

Maximum - Minimum

Question 13

What is the interquartile range?

Answer 13

The middle half of the data set

(25%-75%)

Question 14

What is the standard deviation?

Answer 14

How far each point is from the centre of mass.

Question 15

If your data is normal, what percentage of the population is within 1 standard deviation of the mean?

Answer 15

68%

Question 16

If your data is normal, what percentage of the population is within 2 standard deviations of the mean?

Answer 16

95%

Question 17

If your data is normal, what percentage of the population is within 3 standard deviations of the mean?

Answer 17

99%

Question 18

What is the R command for calculating standard deviations?

Answer 18

sd()

Question 19

The symbol s refers to?

Answer 19

The standard deviation of a sample

Question 20

The letter σ represents?

Answer 20

The standard deviation of a population.

Question 21

What is the formula for standard deviations?

Answer 21

The square root of the variance.

Question 22

What is variance?

Answer 22

The average of the squared differences from the Mean.

Question 23

What are the four steps for calculating the variance?

Answer 23

1. Work out the Mean (average)
2. For each number: subtract the Mean and square the result (the squared difference - to avoid negatives and positives cancelling each other out)
3. Calculate the average of those squared differences
4. Divide the average of the squared differences by N for population data or N-1 for sample data

Question 24

What is the difference between calculating variance when using population data or sample data?

Answer 24

Population data = divide by N when calculating Variance

Sample data = divide by N-1 when calculating variance

Question 25

Why can SD’s help determine clinical significance?

Answer 25

Tell us what is normal or abnormal.

Question 26

What descriptive statistics should you use to describe nominal scale variables?

Answer 26

Frequency Tables

Question 27

What are frequency tables?

Answer 27

A table consisting of the number of times you see each observation.

Question 28

When do you use ‘cross tabulation’?

Answer 28

When you want to look at nominal variable relationships.

(e.g. males with brown eyes, females with green eyes etc.)