MathBench > Statistics

Bar Graphs and Standard Error

How to make a fancier bar chart

We're not even going to practice making bar charts, but we'll go right on to adding bells and whistles.

Remember that your boss wants you to show that Fish2Whale is better than the competitor brands (Budget Fude, Ballmart, and Fish-O-Matic). On the first screen, I showed one possible graph:

bar chart comparing Fish2Whale to 3 competitors

To make this graph, your boss started with 4 equal-size fish and fed one type of food to each fish. Although the results are certainly promising (the Fish2Whale fish ended up considerably bigger than the other 3 fish) it is far from being a slam-dunk.

Most importantly, your boss only tested each food on a single fish. As we discussed in the module on the Normal Distribution, virtually all scientific experiments involve some level of natural variability. Some fish are naturally larger, stronger, happier, whatever... and they grow faster.

So what you need to do is repeat -- or more impressively, to "replicate" -- your treatements using several similar fish.

lots of fish

Time passes.

Fish grow.

Finally the results of your experiment are ready... good news for the company. Here is your datatable, and a possible graph:

Fish # 1 2 3 4 5 6 7 8 9 10 11 12
Brand BF BF BF Bmart Bmart Bmart F-O-M F-O-M F-O-M F2W F2W F2W
Final Length (mm) 16 17 18 14 17 20 12 17 22 19 22 25



bar chart with 12 bars

Hmm, this graph is kinda funny looking. Other than a criminal use of gradient fills, what did your boss do wrong?

Drawing 12 bars seems like a little bit of overkill. Maybe there is a way to summarize the data?

What we really want to know is, what was the AVERAGE growth for each type of fishfood, right? So let's try taking some averages. Now our datatable looks like this:

Fish # 1 to 3 4 to 6 7 to 9 10 to 12
Brand BF BMart F-O-M F2W !!
AVERAGE Final Length (mm) 17 17 17 22


And your new, improved graph looks like this:

bar chart with 4 bars