From overcomplicating or overdressing our charts, to conveying an entirely inaccurate message, there are common design pitfalls that can easily be avoided. We’ve put together these pointers to help you create simpler charts that effectively get across the meaning of your data.

In a world where data really matters, we all want to create effective charts. But data visualization is rarely taught in schools, or covered in on-the-job training. Most of us learn as we go along, and therefore we often make choices or mistakes that confuse and disorient our audience.

“Most people will believe whatever you tell them as long as a chart is involved,” researchers found in a 2014 study “Blinded with science.” Given the persuasive power of charts, it’s important we use them correctly and put our audience’s best interests at the heart of our design. There are many different ways a chart can accidentally communicate the wrong message, distort the truth, or make the data difficult, if not impossible, to decipher and consume quickly.

Many charts have sophisticated and intelligent underlying information, but their presentation fails to convey the intended message

Bar charts are great for comparisons. To judge their end points, the bars should begin at a zero baseline. For people to draw meaningful conclusions from a bar graph, the bars have to be presented in full. To do this, you need to start your vertical axis at zero. Bar charts are generally easy to read because they “ask” our eyes to do a simple thing: compare the relative heights of the bars. But if we show just the tips of the bars to exaggerate differences in the data, our audience loses the ability to make useful visual comparisons. “Truncation equals misrepresentation,” writes Dona M. Wong. So people are either misled and take away the wrong message, or end up having to read the numbers, which defeats the purpose of the chart.

Line charts often show a trend. Stretching the height of the graph can create fake drama, while stretching the width can underplay it. Similar to a stretched or squished photo, a chart’s dimensions — or its aspect ratio — can change the image that we’re presenting. But while you usually can’t get away with a wrong aspect ratio in a photo, a distorted one in a chart can easily go unnoticed. Whether this results in an overblown or understated message, it just misleads your audience. “There is no single rule to follow in terms of how high or wide to make the graph, but a useful notion involves ‘banking to 45°,’ whereby the average slope angle across your chart heads towards 45°,” writes data visualization specialist Andy Kirk. This is probably impractical to measure, but judging by eye tends to do the trick.

Pie charts seem friendly, but in reality they’re hard to read. In most cases, you can find a better alternative. Pie charts are part of the larger family of area graphs, which are all difficult to interpret. Nevertheless, pie charts are widely used and abused in almost every professional and educational setting. The reason why pie charts are best avoided is straightforward: our brains can’t make accurate estimates or comparisons of angles. If the slices are fairly close in size, it’s difficult — if not impossible — to tell which is bigger, and when they’re not close in size, the best you can do is determine that one is bigger than the other, but you can’t judge by how much, explains data visualization expert Cole Nussbaumer Knaflic. Delivering precise numbers with a pie chart requires a lot of effort, such as relying on direct slice labels that might not fit, or legends that make our eyes jump back and forth between the pie and the legend.