Russel-Research-Method-in-Anthropology

562 Chapter 19
Measures of Central Tendency
Once we have the data laid out and have a feel for what’s in there, we can
start describing the variables. The first thing to do is get some overall measure
of the ‘‘typical’’ value for each variable. This is called a measure of central
tendency.
The three most widely used measures of central tendency are the mode, the
median, and the mean. All these get packaged together in everyday speech
as some kind of ‘‘average,’’ but we have to be more precise in data analysis.
Each measure of central tendency carries important information about the values
of a variable.
Here are the definitions for each of these measures of central tendency:
1. The mode is the attribute of a variable that occurs most frequently. The mode
can be found for nominal-, ordinal-, and interval-level variables, but it is the only
measure of central tendency available for nominal variables.
2. The median is the midpoint in a distribution above and below which there are
an equal number of scores in a distribution. The median can be found for ordinal-
and interval-level variables.
3. The mean, or the average, is the sum of the individual scores in a distribution,
divided by the number of scores. The mean can be found for ordinal- and interval-level
variables.
Central Tendency: The Mode
The mode is the attribute of a variable that occurs most frequently. Technically,
the mode is not calculated; it is observed. You find it by simply looking
at the data and seeing which attribute of a variable occurs the most. In table
19.3b, we see that the modal value for education is 12 years (there are 8 out
of 30 cases). This tells us that finishing high school is the most common level
of education in our sample of 30 respondents.
All variables (nominal, ordinal, and interval) have modal values, but nominal
variables can only have modal values. In table 19.3a, for example, we see
that there are 18 men (GENDER 1) and 12 women (GENDER 2). The
mode, then, is male for this sample of 30. (The mode, by the way, was female
for the full survey of 609 respondents. When you work with small samples,
fluctuations of this magnitude are normal.)
Many distributions have more than one mode, and bimodal distributions are
quite common. In a rural community that has experienced a lot of out-migration,
for example, the age structure is likely to be bimodal: There are young