Start your bar charts from zero – Excel geeks screaming at you from mountain top

Posted on May 15th, 2017 in Charts and Graphs - 22 comments

Here is a simple but vital charting rule.

Start your bar (or column) charts from zero.

To illustrate why you should do this, let me share a personal example.

Over the weekend, the Jon Peltier visited Wellington. He is staying with Jeff (who occasionally guest blogs on Chandoo.org). On Sunday, we all decided to hike up a small mountain near my house for a leisurely family picnic.

While on the top of the mountain, Jo (my wife) took a few pics of us three Excel geeks.  As we were standing on a sloping mountain face this is how the pictures look:

start-your-axis-at-zero-bar-charts

Looking at the picture on left, you would confidently say that I am way shorter than other two. But picture on right tells a different story.

Of course, the reality is somewhere between two pictures. It is difficult to conclude who is tall, who is short just looking at the pics simply because the baseline is sloping. 

But we can’t have sloping baselines in Excel charts

You are right we can’t. But we can still confuse people with an arbitrary axis start. Like below:

bar-chart-with-arbitrary-axis

The fix? always start your axis at zero for bar (or column) charts:

Simple. Set the axis start point to zero (Select axis, press Ctrl+1, and from Axis options set minimum to 0).

bar-chart-with-zero-axis

So there you go. The shortest Excel charting tip ever, but still stands tall when it comes to telling great stories.

More charting principles:

If you are in the mood for some more charting theory and elegant methods, check out below links.

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22 Responses to “Start your bar charts from zero – Excel geeks screaming at you from mountain top”

  1. Chris Chua says:

    Great illustration to drive home the point. Makes me lmao.

    Then again coming from a math/statistic background, statisticians sometimes do purposely start with a non-zero axis or log axis to "provide" a visual trend to what they want to convey.

  2. Jeff Weir says:

    Haha. I'm like two times louder than you, but you have two times the amount of hair on your head than I do!

  3. Jon Peltier says:

    How many Excel geeks does it take to teach a simple lesson?
    I had aa awesome stay in Wellington, and it was great meeting Chandoo for the first time and catching up with Jeff.

  4. GraH says:

    Too much Excel power on that hill for sure! But what a view it is.

  5. Ken says:

    Like many things in life...it depends. The example given is to show differences in height. So the non-zero base causes a misleading visual. However, if you are tracking the growth rate of secured loan pools across years by month and want to show a rolling 13 month view, then a non-zero base would work just fine. Specifically if the loan pools are growing by a positive rate over time. Some would say use a line. Except it is useful to also compare the month to month growth rate using the same chart. This allows the differences in rate to 'pop out' for the viewer (considering the y axis in tens of thousands of units).

    • Themistocles says:

      That.

      What is the purpose of charts? Why, to convey information, of course. If they don't do their job then they are wrong.

      I read Darrell Huff almost 25 years ago and of course I always look for the axis when I see a chart, so naturally I have an aversion for non-zero starts.

      However, there are many, many variables where a miniscule change has a great significance - think blood values, perhaps, or financial figures. If I'm presenting to our board of directors and use a zero-start axis all I'm showing them is a series of very long, equal bars. Amount and value of information given: zero, like the beginning of the axis.

      So: in essence, I agree. But the technique absolutely does have its purpose.

      • Jon Peltier says:

        Did you notice the title of the article? "Start your BAR charts from zero". So chart type is an important aspect of this discussion.

        The value of a bar is encoded by the length of the bar, and a comparison of the bar's length to other bars' lengths. If you cut off the bottom of the bar, then the encoding is incorrect, and no amount of conscious thought about the axis scale will overcome the eye's and brain's precognitive judgement of the value of the bar.

        The value of a marker is encoded by the position of the marker along a scale, and a comparison of the marker's position to other markers' positions. If you need to show small differences, either plot actual deltas, or plot the values in a marker-containing chart (line or scatter).

        • Themistocles says:

          While I agree with what you say, the point remains that such extreme bars convey no information whatsoever. So something must be done. Bias, sure, but it cuts both way - perceiving them the same when the difference is huge in significance is also a bias.

          Now deltas is a great idea indeed and much closer to the spirit as it should be - you could even add labels for absolute values. However, this is not foolproof either.

          Consider this: my corporate site may load at, say, five seconds. Flutter may indicate a problem, though that flutter is small. Plotting deltas, if a small scale is used, provides the information needed. However, for various reasons, a much bigger delta may be introduced, pushing all the other data points much closer together. So back at square one, hacking away at it trying to make it show something real...

  6. Amar says:

    very nice… i really like your blog…
    Really I'm Very Thankful to You, n I like The Posts in The way You Write/ Compose Keep Going On All The Best !!!

  7. John says:

    The Excel version of Mount Rushmore?

  8. Neil Hoskins says:

    This is a really nice illustration. We have a very popular nature show on TV here called "Springwatch" and the other day the presenter showed a graph that seemed to show that British Isles farmland birds were totally extinct. They have actually decreased by about 42% IIRC, but it's a bit naughty to start the y-axis at 58%

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