DATA TABLES…

KINDS OF VARIABLES…

Qualitative vs. Quantitative

Discrete vs. Continuous

DISPLAYING a QUALITATIVE VARIABLE

MORE about HISTOGRAMS

DATA TABLE

parties politics salary singer

5 mod. 80000 1.5

1 liberal 35000 3

3 liberal 3

2 mod. 40000 4

2 liberal 40000 0

DATA TABLE

parties politics salary singer

5 mod. 80000 4.5

1 liberal 35000 3

3 liberal 3

2 mod. 40000 4

2 liberal 40000 0

Rows

Columns

CASES

INDIVIDUALS

whatever

VARIABLES

Kinds of Variables

QUALITATIVE —

Nominal — Just labels

Ordinal — Order matters

QUANTITATIVE —

Discrete — Only certain values(for example, whole numbers)

Continuous — Any value is possible

(at least in some range)

DISPLAYING ONE QUALITATIVE VARIABLE

Frequency table…

Bar chart…

Pie chart…

Frequency table - politics

VALUE COUNT

Liberal 20

Moderate 3

Conservative 2

TOTAL 25

Frequency table - politics

VALUE COUNT PERCENT(of column)

Liberal 20 80 %

Moderate 3 12 %

Conservative 2 8 %

TOTAL 25 100%

Frequency table – politics (Swarthmore)

VALUE COUNT PERCENT(of column)

Liberal 46 64%

Moderate 22 31%

Conservative 4 6%

TOTAL 72 100%

Frequency table – singing

VALUE COUNT PERCENT

1 10 39 %

2 6 23 %

3 6 23 %

4 2 8 %

5 2 8 %

TOTAL 26 100 %

Frequency table – singing

VALUE COUNT PERCENT

1 10 39 %

2 6 23 %

3 6 23 %

4 2 8 %

5 2 8 %

TOTAL 26 101 %

Frequency table – singing

VALUE COUNT PERCENT

1 10 38 %

2 6 23 %

3 6 23 %

4 2 8 %

5 2 8 %

TOTAL 26 100 %

Frequency table – singing (Swarthmore)

VALUE COUNT PERCENT

1 16 22%

2 16 22%

3 23 32%

4 12 17%

5 5 7%

TOTAL 72 100%

12345

Singing

0

2

4

6

8

10

12

1 2 3 4 5

EQUAL-AREA PRINCIPLE

Areas are in proportion to data values.

Salaries (Swarthmore)

600000 60000 50000 60000 50000 30000

50000 50000 30000 very small 250000

75000 30000 70000 60000

70000 80000 125000 50000

35000 65000 50000 70000 80000

200000 30000 400000 72500 60000

80000 40000 30000 150000 75000 40000

120000 40000 40000 20000 60000

500000 75000 30000 60000 45000

40000 85000 35000 90000 150000

150000 50000 100000 45000 30000 80000

100000 50000 1000000 100000 50000

Salaries - $20,000 bin sizes

$50,000 bin sizes

$100000 bin sizes

Constructing a histogram…

Define binsAll the same size ? Easier if they are, but…Boundaries – ENDPOINT RULE

Make a frequency table for your chosen bins…

Construct histogram…

Shape of a distribution…

Symmetrical ?Skew – right or left

UnimodalBimodal Multimodal

Outliers