Russel-Research-Method-in-Anthropology

48 Chapter 2
between 70 and 80, and the difference between an IQ score of 90 and 100 is
(assumed to be) the same as the difference between one of 130 and 140. On
the other hand, 80 Fahrenheit is not twice as hot as 40, and a person who has
an IQ of 150 is not 50% smarter than a person who has an IQ of 100.
Ratio variables are interval variables that have a true zero point—that is,
a 0 that measures the absence of the phenomenon being measured. The Kelvin
scale of temperature has a true zero: It identifies the absence of molecular
movement, or heat.
The consequence of a true zero point is that measures have ratio properties.
A person who is 40 years old is 10 years older than a person who is 30, and a
person who is 20 is 10 years older than a person who is 10. The 10-year intervals
between the attributes (years are the attributes of age) are identical. That
much is true of an interval variable. In addition, however, a person who is 20
is twice as old as a person who is 10; and a person who is 40 is twice as old
as a person who is 20. These, then, are true ratios.
While temperature (in Fahrenheit or Celsius) and IQ are nonratio interval
variables, most interval-level variables in the social sciences are also ratio variables.
In fact, it has become common practice in the social sciences to refer
to ratio-level variables as interval variables and vice versa. This is not technically
pure, but the confusion of the terms ‘‘interval’’ and ‘‘ratio’’ doesn’t cause
much real damage.
Some examples of ratio variables include: age, number of times a person
has changed residence, income in dollars or other currency, years married,
years spent migrating, population size, distance in meters from a house to a
well, number of hospital beds per million population, number of months since
last employment, number of kilograms of fish caught per week, number of
hours per week spent in food preparation activities. Number of years of education
is usually treated as a ratio variable, even though a year of grade school
is hardly worth the same as a year of graduate school.
In general, concepts (like alienation, political orientation, level of assimilation)
are measured at the ordinal level. People get a high score for being ‘‘very
assimilated,’’ a low score for being ‘‘unassimilated,’’ and a medium score for
being ‘‘somewhat assimilated.’’ When a concept variable like intelligence is
measured at the interval level, it is likely to be the focus of a lot of controversy
regarding the validity of the measuring instrument.
Concrete observables—things you can actually see—are often measured at
the interval level. But not always. Observing whether a woman has a job outside
her home is nominal, qualitative measurement based on direct observation.