Table of contents

  1. Choosing the correct chart
  2. Choice of data
  3. Comparing data sets – shared horizons
  4. Comparisons of magnitude (size)
  5. Time series
  6. Bar charts for time series
  7. Line charts for time series
  8. Dot plot with line for time series
  9. Multiple time series
  10. Small changes over time, not starting the y-axis at zero
  11. Ranking
  12. Part-to-whole
  13. Deviation
  14. Distribution
  15. Correlation

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Small changes over time, not starting the y-axis at zero

Time series charts do not have to begin at zero, if a chart does not start at zero this must be indicated by breaking the y-axis in an obvious way.

Scale of the axes

A chart can tell a very different story depending on the scale of the axes.

This chart gives the impression that the measles, mumps and rubella (MMR) vaccination level has remained high and fairly stable.

Example of chart with the y-axis at zero showing a fairly stable trend

An overview

MMR vaccination uptake at age 1 year
UK, 1992 to 2012

A line chart with the y axis starting at zero, suggesting that the vaccination level for measles, mumps and rubella has remained fairly high and stable.

When the y-axis is altered a different picture emerges showing that the measles, mumps and rubella vaccination has dropped considerably since 1997.

Example of chart with the y-axis altered showing a more dramatic trend

A more focused view

MMR and Diphtheria vaccination uptake at age 1 year
UK, 1992 to 2012

A line chart with a break in the axis at 75% showing that the measles, mumps and rubella vaccination has dropped considerably since 1997

You can use two charts with different axes scales to ensure that the data are represented without bias whilst highlighting the important message.