Module 3: Data Visualization

Question 1

Data visualization

Answer 1

A distribution of a variable is a description of the values it can take on, & a count of how often each value occurs

Question 2

Sample distributions

Answer 2

The distribution of a sample we obtain from a population - lists the possible outcomes & the number of times each occurs in this sample

Question 3

One observation

Answer 3

One unit in the sample (or single coin flip result)

Question 4

Assess the distribution

Answer 4

We want to describe the distribution in a useful way to enable subsequent analysis - shape, extreme values, centre, & spread

Question 5

Shape of distribution

Answer 5

Left/negatively skewed: the mean is less than the median Right/positively skewed: the mean is greater than the median symmetric: the mean & the median are equal

Question 6

Centre of the distribution

Answer 6

Use a measure of central tendency: the mean, median or mode. Report the median if you have a skewed distribution - report the mean if you have a symmetric distribution

Question 7

Spread of distribution

Answer 7

Use a measure of variation: the range, mean absolute deviation(MAD), variance, & standard deviation - for boxplot use the interquartile range (IQR)

Question 8

Spread (visually)

Answer 8

Evaluated visually by looking at the relative heights of the bars

Question 9

The 5 number summary

Answer 9

-the minimum (min) -Q1(the 25th percentile) -the median (Q2, the 50th percentile -Q3 (the 75th percentile) -the maximum (max)

Question 10

EXCEL percentiles

Answer 10

Q1=percentile.exc(values, 0.25) - Q2=percentile.exc(values, 0.50) - Q3=percentile.exc(values, 0.75)

Question 11

Percentiles

Answer 11

The pth percentile of a data set is the value such that p percent of the observations are less than or equal to the value

Question 12

Quartile

Answer 12

A quartile of a data set is the 25th percentile (Q1, Q2, Q3)

Question 13

The interquartile range (IQR)

Answer 13

A measure of spread of a data set, & is the difference between Q3 & Q1 - IQR= Q3-Q1

Question 14

The inner fence

Answer 14

1.5 x IQR. - if a sample value is greater than Q3 + inner fence, or less than Q1 - inner fence it is extreme

Question 15

Lower whisker

Answer 15

(Q1 - IF, Q1)

Question 16

Upper whisker

Answer 16

Q3, Q3 + IF)

Question 17

Histogram

Answer 17

Used to portray the frequency of sample values: the number of times a value within a certain interval occurs on the data set

Question 18

Table of relative frequency

Answer 18

A numerical summary of a data set, related to a histogram

Question 19

Class

Answer 19

Refers to each bin in the corresponding histogram

Question 20

Frequency

Answer 20

The number of occurrences of a class in a data set

Question 21

Relative frequency

Answer 21

The fraction of the number of occurrences of a class in a data set, out of the total number of elements on the data set, expressed as a decimal

Question 22

Cumulative relative frequency

Answer 22

The relative frequency of each class, added to the relative frequency of all previous classes in the table

Question 23

Contingency table

Answer 23

Used to compare the distributions of 2 or more categorical variables