Russel-Research-Method-in-Anthropology

54 Chapter 2
Reliability
Reliability refers to whether or not you get the same answer by using an
instrument to measure something more than once. If you insert a thermometer
into boiling water at sea level, it should register 212 Fahrenheit each and every
time. ‘‘Instruments’’ can be things like thermometers and scales, or they can
be questions that you ask people.
Like all other kinds of instruments, some questions are more reliable for
retrieving information than others. If you ask 10 people ‘‘Do the ancestors
take revenge on people who don’t worship them?’’ don’t expect to get the
same answer from everyone. ‘‘How many brothers and sisters do you have?’’
is a pretty reliable instrument (you almost always get the same response when
you ask a person that question a second time as you get the first time), but
‘‘How much is your parents’ house worth?’’ is much less reliable. And ‘‘How
old were you when you were toilet trained?’’ is just futile.
Precision
Precision is about the number of decimal points in a measurement. Suppose
your bathroom scale works on an old-fashioned spring mechanism. When you
stand on the scale, the spring is compressed. As the spring compresses, it
moves a pointer to a number that signifies how much weight is being put on
the scale. Let’s say that you really, truly weigh 156.625 pounds, to the nearest
thousandth of a pound.
If you have an old analog bathroom scale like mine, there are five little
marks between each pound reading; that is, the scale registers weight in fifths
of a pound. In terms of precision, then, your scale is somewhat limited. The
best it could possibly do would be to announce that you weigh ‘‘somewhere
between 156.6 and 156.8 pounds, and closer to the former figure than to the
latter.’’ In this case, you might not be too concerned about the error introduced
by lack of precision.
Whether you care or not depends on the needs you have for the data. If you
are concerned about losing weight, then you’re probably not going to worry
too much about the fact that your scale is only precise to the nearest fifth of a
pound. But if you’re measuring the weights of pharmaceuticals, and someone’s
life depends on your getting the precise amounts into a compound, well,
that’s another matter.
Accuracy
Finally, accuracy. Assume that you are satisfied with the level of precision
of the scale. What if the spring were not calibrated correctly (there was an