Study Notes
Histograms are specialised graphs used to show the distribution of continuous or grouped data, where the area of the bars represents the frequency. They are similar to bar charts but have no spaces between the bars because the horizontal scale is continuous.
- Histogram — a graph showing the distribution of continuous data with bars touching each other. Example: A histogram showing the heights of plants with class intervals on the x-axis and frequency density on the y-axis.
- Frequency Density — a measure used when class intervals are unequal, calculated as frequency divided by class width. Example: For a class interval of 5 ≤ h < 15 with 4 plants, frequency density is 0.4.
- Class Interval — a range of values in a histogram that each bar represents. Example: The interval 20 ≤ h < 25 represents plant heights between 20 and 25 cm.
Exam Tips
Key Definitions to Remember
- Histogram: A graph for continuous data where the area of each bar represents frequency.
- Frequency Density: Used when class intervals are unequal, calculated as frequency divided by class width.
Common Confusions
- Mistaking histograms for bar charts due to their similar appearance.
- Using bar height instead of area to determine frequency in histograms.
Typical Exam Questions
- How do you calculate frequency density? Frequency density = frequency / class width
- What is the difference between a histogram and a bar chart? Histograms show continuous data with touching bars; bar charts show categorical data with spaces between bars.
- How do you interpret a histogram with unequal class intervals? Use frequency density to compare frequencies accurately.
What Examiners Usually Test
- Ability to draw and interpret histograms correctly.
- Understanding the concept of frequency density and its application.
- Differentiating between histograms and bar charts.