1. Representing Data OCR Module 9
HISTOGRAMS
Representing Data
OCR Module 9

2. Why use a Histogram When there is a lot of data When data is
Continuous
a mass, height, volume, time etc
Presented in a Grouped Frequency Distribution
usually in groups or classes that are UNEQUAL

3. NO GAPS between Bars
Continuous data

4. Bars are different in width
Determined by Grouped Frequency Distribution

5. = Frequency Class width So we use FREQUENCY DENSITY
AREA is proportional to FREQUENCY
NOT height, because of
UNEQUAL classes!

6. Grouped Frequency Distribution
Classes
Speed, kph
0< v ≤40
40< v ≤50
50< v ≤60
60< v ≤90
90< v ≤110
Frequency 80 15 25 90 30

7. Drawing Sensible Scales Bases correctly aligned Heights correct
Plot the Class Boundaries
Heights correct
Frequency Density

8. Frequency Densities Speed, kph 0< v ≤40 40< v ≤50 50< v ≤6080 15 25 90 30
Frequency Density
Class width 40 10 10 30 20
2.0
1.5
2.5
3.0
1.5

9. Frequency = Width x Height
Freq Dens
Frequency = 40 x 2.0 = 80
3.0
2.0
1.0 40 20 60 80
100
120
Speed (kph)