Presentation Skills - The Right Graph
Microsoft does not know a heckuva lot about presentation design,
but one thing they do correctly in PowerPoint is to make
available different types of graph so that you can match the
graph type to the point you're trying to make with your data.
There are twelve different graph types available with PowerPoint
2000, but few of those styles work well in the low-resolution
world of computer-based presentations. With few exceptions, here
is how you want to use the following types:
* Pie Graphs for Share * Bar Graphs for Comparative Amounts *
Line Graphs for Trends, Time
Pie Graphs
Pie graphs (commonly misnomered pie charts) are one of the more
overused, and hence misused, types of graphs, primarily because
they are so easy to make, and easy to make look good. They are
misused when chosen to show amounts rather than share. The
beauty of pie graphs is that they show so clearly what they are
supposed to show, i.e., how much of the whole each element
contributes. In most cases the actual amounts - in this case
percentages - are actually secondary to the area of the slices
in terms of telling the story.
When you look at a pie graph with five or fewer slices, your
brain can quickly ascertain which groups dominate. We often see
pie graphs with more than 5 elements, but they then become more
difficult to comprehend in short order. In most cases, consider
whether your story needs to include details about all the
players, or whether a group of insignificant contributors can be
grouped as "others".
If you want to show how much volume each element contributes,
rather than what fraction, you'll want to use a bar graph.
Bar Graphs
To show relative sizes of different segments as well as the
actual amounts, you'll want to use a bar graph. Bar graphs are
designed to show volumes against a y-axis that clearly
delineates the units of measure. By having a series of bars next
to each other, we can see how each element compares with the
others as well as what absolute volume the element represents.
There are variations on the bar graph, such as a stacked bar,
where different elements are stacked on top of each other to
form a series, or a 100% bar graph, where all the bars are the
same height but are split to show what percent of the whole the
volume reflects. In a presentation environment, esoteric options
are best to be avoided.
Line Graphs
Line graphs have the unique advantage of speaking to inherent
right-brain prejudices about information. That is, when
typically conditioned western minds see a graph with no
labeling, they automatically assign "volume" to the y-axis, with
"up" meaning "more", and a time-line to the x-axis, with the
left side meaning most recent. Just as we read from
left-to-right, rightward motion subconsciously means positive
motion. You would want to use a line graph, then, to show a
progression in amount from one point in time to another. The
elevation of the line at any one point represents the quantity
of the tracked data at that moment. Audiences, wanting to be the
first-to-know, will automatically make assumptions about the
types of values x-axes and y-axes represent. Don't disappoint
them.
Data labels
Graphs are a great way of making complex information easily
understood. But graphs work best only when you properly
integrate words, numbers and images. Whenever possible, label
the elements of your graph directly on the elements themselves,
rather than relying on the ever-popular clarity killer, the
legend. Legends require too much effort on the part of listeners
to discern exactly what each data point is. Just be certain your
labels don't clutter up the otherwise clear "picture" a good
graph can make.
If you have a number of graphs in your presentation, you'll want
to avoid dumping a data overload on your audience by
over-labeling each one. In fact, in many cases you can tell your
story forcibly enough by only the size of your data elements,
without burdening their minds with numbers that they're likely
to forget by the end of the presentation. However, it's also not
a bad idea to have what we call "reference slides" that do
contain all the data attached to the end of your main slide
deck. To really impress your crowd, install hyperlinks to these
slides from the ones in your main show, and when some
vice-president makes a stink about wanting to know the whole
story, zap to your total-info slide and give him what he wants.
He probably won't ask again.