A recent article in the Business section of the New York Times referenced a chart which compared recommended nutrition servings to federal subsidies.
http://economix.blogs.nytimes.com/2010/03/09/why-a-big-mac-costs-less-than-a-salad/
(PCRM)
At first glance this chart appears to show a severe imbalance between nutritional needs and federal subsidies of the food industry. But upon closer examination, I found numerous issues with the way information was presented in the chart.
1. The pyramid on the left is an attempt to represent a percentage of food subsidy dollars. The largest percentage of food subsidy dollars go to meat and dairy, claiming 73.8% of the subsidy Assuming these numbers are accurate, the use of a three-dimensional pyramid leads to a skewed representation of the data. The meat/dairy slice, for example, is approximately 73.8% of the height of the pyramid. However, since a pyramid is three-dimensional, the reader is drawn to the height of each slice, but the overall volume (size) of each slice. A slice which is 73.8% of the height of the pyramid (starting from the bottom) actually takes up over 95% of the volume of the pyramid, thus lending the visual impression that the meat/dairy subsidy is significantly larger than it actually is.
The pyramid on the right side of the chart (recommended servings) puts the protein category near the top of the pyramid, thus reversing the effect. The two pyramids, each with their own exaggerations, combine to create a highly distorted message.
2) The pyramid shape also conveys a relationship beyond that of simple size differences. Pyramids are most often used to indicate some level of dependency - that things on the top of the pyramid are somehow dependent on the things at the bottom. That is why we tend to
resort to construction terms and refer to the bottom as the foundation. (I never liked the old "food pyramid" for this same reason. You need all those foods).
3) Finally, in the chart on the left, what does a "percent" actually mean? Does it mean that 73.8% of the cost of meat is subsidized, or does it mean that 73.8% of the subsidy dollars go to meat (as I suggested above)? The difference is important because the cost of producing meat is not the same as the cost of producing grains. Since grains are actually used to feed cattle, it is possible that some of the meat subsidy dollars actually ends up subsidizing grains (ranchers need to purchase grain to feed the cows).
By putting those two pyramids side by side, the suggestion is that one serving of meat or dairy is somehow equivalent to one serving of say, vegetables, and also that the cost of producing a serving of each is roughly the same. Of course, that is not true - meats and vegetables
provide for different nutritional needs, the cost of producing them is different, and both are important to your health.
To do a true comparison, you would first need to choose a format that did not imply dependencies. Then, to be truly fair, you would need to somehow normalize the subsidy side to deal with factors such as differences in cost to produce, nutrition density (you get all the
protein you need in only 6 servings, but it takes 11 servings of grains to give you what you need, etc.)
It's tempting to enhance the appearance of your charts through effects such as 3-D models, but you have to be careful that the use of such effects does not distort the information you are attempting to display.
