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

Continuous data NO GAPS between Bars

Bars are different in width Determined by Grouped Frequency Distribution

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

Grouped Frequency Distribution Speed, kph0< v ≤4040< v ≤5050< v ≤6060< v ≤9090< v ≤110 Frequency Classes

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

Speed, kph0< v ≤4040< v ≤5050< v ≤6060< v ≤9090< v ≤110 Frequency Frequency Density Class width Frequency Densities

Freq Dens Speed (kph) Frequency = Width x Height Frequency = 40 x 2.0 = 80

How do we treat ages? Age, Years15 – 1920 – 2425 – 3435 – Frequency Consider this frequency distribution of the ages of visitors to a department store Class width Freq Dens ‘15 – 19’ has an UPPER LIMIT of the 20 th birthday