Histogram
Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 4 "Presentation of Data"; Class 11, Ch 8 "Use of Statistical Tools"
Meaning
A histogram is a set of rectangles drawn side by side with no gaps, one on each class interval. The area of each rectangle matches the class frequency. This makes it a two-dimensional diagram: both width and height matter. When classes have equal widths, height can simply be the frequency. When the widths differ, height must be the frequency density (class frequency ÷ class width). A histogram is drawn only for continuous data, meaning data that can take any value, such as wages or height. It is also used to find the mode (the most common value) on a graph.
Example
NCERT draws a histogram of the daily wages of 85 earners. The tallest rectangle marks the modal class. Lines drawn from the corners of this rectangle to the corners of its neighbours cross at the mode.
Don't confuse with
- Bar diagram: this is one-dimensional, so only height matters. Its bars have equal gaps between them, and it suits discrete data and attributes.
- Ogive: the median is read from an ogive, not from a histogram.
Related concepts
- Raw data
- Classification
- Chronological classification
- Spatial classification
- Qualitative classification
- Quantitative classification
- Attribute
- Continuous variable
- Discrete variable
- Frequency