|This page in a nutshell: While some charts may contain accurate data, if not done to scale they may present readers with the wrong impression.|
Interval scale charts
Examine the following interval scale chart. By examining the height of the bars, there seems to be as twice as many cats that are pets compared to dogs. Note the scale of the Y axis starts at 74 million.
Ratio scale charts
Now look at the following ratio scale chart, where the scale starts at zero. The visual difference between the bars representing cats and dogs is much less noticeable. This because the ratio scale chart shows the entire range of data.
Using interval charts to deceive
Though each chart uses the same data, the ratio scale chart presents a visual that accurately presents the data. In the above examples, the interval chart shows a magnified subsection of the ratio chart. A common example of this type of interval magnification is used in charting stocks. A chart may indicate severe price swings because the chart only shows a portion of the range. When the entire price range is shown, the volatility is much less noticeable. A stock broker who earns fees from commissions can take advantage of interval ratio charts by using perceived volatility to encourage their customers to place more orders.
When using charts and graphs in articles, make sure the visual representation of the data is not deceptive.