Russel-Research-Method-in-Anthropology

580 Chapter 19
Figure 19.8. Frequency polygon for LEXFEM in Table 19.8.
This is no sampling artifact, either. The big leptokurtic (tall, thin) bulge on
the right covers countries in which women can expect to live, on average,
about 77 years. The platykurtic (wide, flat) bulge on the left covers countries
in which women can expect to live, on average, just 55 years.
The moral is: Examine the frequency distribution for each of your variables.
For interval and ordinal variables, find out if the distributions around the mean
or median are symmetrical. If the distributions are symmetrical, then the mean
is the measure of choice for central tendency. If the distributions are skewed,
then the median is the measure of choice. And if the distributions are bimodal
(or multimodal), then do a much closer examination and find out what’s going
on.
Measures of Dispersion I: Range and Interquartile Range
After central tendency and shape, the next thing we want to know about
data is something about how homogeneous or heterogeneous they are—that
is, something about their dispersion or variation The concept of dispersion is
easily seen in the following example. Here are the ages of two groups of five
people:
Group 1: 35 35 35 35 35
Group 2: 35 75 15 15 35