A logarithmic graph has a series of open and grouped vertical lines in which the top and bottom of each group, called a cycle, is a decimal or multiple of ten. It is
Number of Flowering Plant Species in West Suffolk County
Fig. 3.5. In this effective pictograph, the length of the flower stems corresponds to the number of plant species.
ยป -10 cases of heal disease
1971 -1960 1981-1990 1991-2000
Increase in heart disease reported to the We 11 hear) Clinic during the past thirty years
Fig. 3.6. A pictograph that uses heart symbols to show disease incidence effectively reflects the subject of the graph.
commonly but not exclusively used to compare data in which rate of change is more important than quantity of change. (An exception sometimes encountered in medical writing is the dose-response curve. Dose is logarithmically related to response in terms of number of receptors stimulated.) A logarithmic graph also is frequently used when the vertical range is so large that it is difficult to fit on a normal graph. However, because nonscientific readers may not be familiar with a logarithmic scale, they can find such graphs confusing.
Scatter graphs, which sometimes are charted logarithmically, use single unconnected dots to plot instances where two variables (one on each axis) meet (Fig. 3.7). The pattern of the dots expresses the relationship (a diagonal trend, which is sometimes approximated by a line on the chart) or lack of a relationship (random scatter) between the variables. Interpreting scatter graphs also can be difficult for nonscientific readers.
60 cases 80 cases 220 cases
Fig. 3.7. This scattergraph shows that larger male wasps, as measured by head width, have greater mating success.
Head width (mm)
Fig. 3.7. This scattergraph shows that larger male wasps, as measured by head width, have greater mating success.
If you choose to use either of these graphing techniques, it is imperative that their significance be explained and discussed clearly in the text.
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