Representing Data OCR Module 9 HISTOGRAMS Representing Data OCR Module 9

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

NO GAPS between Bars Continuous data

Bars are different in width Determined by Grouped Frequency Distribution

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

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

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

Frequency Densities Speed, kph 0< v ≤40 40< v ≤50 50< v ≤60 80 15 25 90 30 Frequency Density Class width 40 10 10 30 20 2.0 1.5 2.5 3.0 1.5

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)