# 20.5 Column & Bar Graphs

## This activity is from the Sourcebook for Teaching Science.

Spreadsheet programs allow users to plot data in columns. This is particularly useful when the dependent variable is neither continuous nor evenly spaced, or when the researcher wants to highlight specific divisions of data. Column and bar graphs include the following forms: columns, stacked columns, Pareto, bar and clustered bar, each of which has advantages for displaying certain types of data. The following activities demonstrate the usefulness of column and bar graphs in science.

Activity 20.5.1 – Column chart: Comparing between different items

A column graph allows for comparisons between different items. Categories are organized horizontally and values vertically. Figure 20.15B shows the population profiles of the United States and Afghanistan in 2000. The vertical axis represents the percentage of the population in a particular age bracket. Note that Afghanistan had a much younger population than the United States, with a very small older population. Such differences result from the high birth rates and low life expectancies characteristic of many developing nations.

(1) Biology: Population profiles: Plot the population age profile for Germany using data from figure 20.15A. Does this profile more closely resemble that of the United States or Afghanistan? Explain. Obtain population profile data of three countries of your choice from the United States Census Bureau website or other reputable source, [sciencesourcebook.com, or www.census.gov] create column graphs, and determine if their population profiles more closely resemble those of developed or developing nations.

(2) Ecology: Wolf repopulation in Yellowstone: In the 19th century, ranchers, farmers and hunters made a concerted effort to eradicate wolves from the western United States. Wolves are a predatory animal that travel in packs and were seen as a nuisance for ranchers and farmers because they prey on livestock and other animals. Removing wolves upset the food web and allowed for the excessive growth of elk and deer populations, which subsequently overgrazed rangelands and woodlands. In 1995 the National Park Service reintroduced wolves into Yellowstone National Park in order to re-establish the natural balance. The wolves were originally introduced in the northern range of the park, but have now spread to other regions. Produce a column graph of the wolf population of the northern range compared to the park as a whole using the data in Figure 20.15C[i]. Describe the growth and distribution of the wolf population between 1995 and 2003.

Activity 20.5.2 – Stacked column charts: Comparing within and between groups

A stacked column chart allows for comparison between items in a group, as well as between groups. Figure 20.16B is a stacked column plot of the snowfall by month at Mammoth Mountain, California, one of America’s premier ski resorts. One can compare snowfall in the same month in subsequent years by examining a single column. Alternatively, one can compare the average snowfall from month to month by comparing the heights of columns.

(1) Environmental Science: Rechargeable batteries: Batteries have become an essential commodity in developed societies, powering a wide array of portable electronic devices. People use rechargeable batteries because they seem more environmentally friendly than disposable ones. Unfortunately, one of the most popular rechargeable varieties, the nickel-cadmium, contains a toxic heavy metal (cadmium) that has been found in aquifers, probably as a result of leaching from batteries dumped in landfills. Recognizing the need to produce more environmentally friendly rechargeable batteries, chemists developed the nickel-metal-hydride, and eventually the lithium battery. Table 20.3[ii] shows the transition in rechargeable battery sales from 1992 to 1997. Plot this data in stacked columns, so that each column shows percent market share of each battery type each year.

Activity 20.5.3 – Pareto charts: Ranking data graphically

A Pareto chart is a specialized form of a column chart in which the categories are arranged so that the tallest bar is on the left, descending to the shortest bar on the right. Generally, the space between subsequent columns is removed. By arranging the bars in order of height, attention is given to the more important categories. Figure 20.17A illustrates the elemental composition of the human body in descending percent from hydrogen to sulfur, clearly showing that the body is made up mostly of hydrogen, oxygen and carbon.

(1) Earth science: Seawater composition: Seawater is uniformly saline, meaning that the relative concentration of ions is similar throughout the world. Minerals and ions enter the ocean via rivers, thermal vents, volcanoes, and the leaching of rocks on the ocean floor. Water evaporates from the surface of the ocean, leaving behind minerals and ions that make ocean water “salty”. Create a Pareto chart of the main ions found in seawater using the data in figure 20.17B.

(2) Ecology: Threatened and endangered species. In 1973, the United States passed the Endangered Species Act, regulating a wide range of activities that might affect species threatened with extinction. An organism is classified as “endangered” if it is in immediate danger of extinction, and “threatened” if it is likely to become endangered in the foreseeable future. The law protects threatened and endangered species and requires the protection of habitat necessary for their survival and recovery. Using data from figure 20.17C, create a Pareto graph showing the states with the most rare and endangered species. Offer an explanation for the large numbers of endangered species in the top two states.

Activity 20.5.4 – Bar charts: Graphing qualitative independent variables

A bar chart is similar to a column chart, but the axes are reversed. Bar charts are best suited for qualitative independent variables. Figure 20.18 shows the mineral composition of the Earth and Earth’s crust. The independent variable is mineral type, which is a qualitative, discrete variable.

(1) What is the universe made of? Create a bar graph showing the elemental composition of the universe.

(2) What is the atmosphere made of? Create a bar graph showing the elemental composition of the atmosphere.

(3) What is the ocean made of? Create a bar graph showing the elemental composition of the oceans.

(4) What are humans made of? Create a bar graph showing the elemental composition of the human body. Is the composition of the human body more similar to the Sun, the atmosphere, or the oceans?

Activity 20.5.5 – Clustered bar charts: comparing composition of various items

A clustered bar cart allows for rapid comparison of the composition of different items. For example, figure 20.19 shows the comparative composition of vegetable oils. A quick glance reveals that coconut oil has a very high percentage of saturated fats, while safflower oil has a very low percentage. Nutritionists advise diets low in saturated fats since they have been shown to stimulate blood cholesterol and contribute to cardiovascular diseases. The clustered bar chart allows consumers to make a quick comparison between different oils.

(1) Physiology: Is blood type distribution the same for all ethnicities? Human blood is classified as A, B, AB or O, depending upon whether it contains the A-antigen, B-antigen, both the A and B-antigens, or neither. Although blood transfusions may be necessary to sustain life following accidents or surgery, the wrong mixture of blood types may be fatal. For this reason, blood specialists must classify all donor blood according to type. Construct a clustered bar chart from the data in table 20.4 and summarize any significant differences in the distribution of blood types between these groups.

[i] Smith, D., Stahler, D., and Guernsey, D. (2004). Yellowstone Wolf Project: Annual Report, 2003. Yellowstone National Park, WY: National Park Service.

[ii] California Department of Water Resources. (2007). Snow Course Data. Retrieved May 1, 2007 from http://cdec.water.ca.gov.