Central tendency plots

Such a plot identifies the nature of our data, visually classifying them into those that will not influence our analysis (in the set shown, clearly scores of 0 fit into this category) and those that will critically influence the outcome of an analysis. In so doing, the position of control (normal) observations is readily revealed as a central tendency in the data (hence the name for this technique). 

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Figure 4.4. Plotting central tendency. Possible individual scores for righting reflexes may range from 0 to 8 (Gad, 1982a). Group total scores would thus range from 0 to 40. (Shown are the number of groups that contain individual scores in the individual categories.)...

Box Plot This plot is useful when analyzing the pattern of the data. It displays several important features of data such as central tendency, variability, departure from symmetry, and presence of outliers. 

Alternative approaches using box and whisker plots, pie charts and different types of visualizations of density functions are discussed in Ibrekk Morgan (1987) and Morgan Henrion (1990). Each has advantages for specific tasks, but the performance of a display depends upon the information that a subject is trying to extract (central tendency or variation). 

Ward and Loftis (1986) recommend the calculation of measures of central tendency, such as arithmetic means, or geometric means if data are highly skewed, and the plotting of these on charts or graphs as the easiest method for communicating differences in environmental quality to the public and environmental managers. Confidence limits should be reported always with measures of central tendency, such as means and lethal concentration (LC)/effective concentration... 

Using the histogram in Figure 5.1 and the stem-and-leaf plot in Figure 5.2, comment on the appropriateness of each of the following measures of central tendency ... 

In Figure A2 wiien size is plotted against fiequency a skewed distribution (positive, ri t-hand ew in figure) usually results. Frequency distributions are characterised by the parameters which measure the central tendency in terms of the mean, median or mode and the dispersion about the central tendency which is the standard deviation. 

For readers who may not be familiar with a box plot, it can be interpreted as follows The top and bottom faces of the box correspond to the 25% and 75% percentiles of the data (e.g., 0.5 nun and 1.5 mm of wear, respectively). The median (50% percentile) is the horizontal line inside the box (at l.Onun of wear). Thus, the box itself represents the interquartile range, or the central tendency of the distribution corresponding to the middle half of the population. The median is the center of the distribution, with half the population lying to either side. Note that the median for the... 

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