Choosing the right graph matters. Use a line graph when both variables are continuous, a bar chart when the independent variable is categoric, and a pie chart to show parts of a whole. Label both axes with the quantity and unit, and use a scale that fills most of the grid.
A line of best fit passes through the middle of the points, with roughly as many above as below. Reading values between measured points is called interpolation and is usually reliable. Extending the line beyond the data is extrapolation, and it is risky because the pattern may change.
Worked example
Pulse rates were measured after 1 and 2 minutes of exercise: 85 and 95. Predict the rate after 1.5 minutes.
- 1.5 minutes is between 1 and 2 minutes.
- So the rate should be between 85 and 95.
Answer:About 90 beats per minute.
Key words
- line of best fit
- a line through the middle of the points
- interpolation
- reading between measured values
- extrapolation
- extending beyond the data
- axis
- a labelled scale on a graph
Practise this
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