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CONTROLLING THE CONTAMINATING EXOGENOUS OR “NUISANCE”VARIABLES 147

CONTROLLING THE CONTAMINATING EXOGENOUS
OR “NUISANCE” VARIABLES

Matching Groups
One way of controlling the contaminating or “nuisance” variables is to match the
various groups by picking the confounding characteristics and deliberately
spreading them across groups. For instance, if there are 20 women among the
60 members, then each group will be assigned 5 women, so that the effects of
gender are distributed across the four groups. Likewise, age and experience fac-
tors can be matched across the four groups, such that each group has a similar
mix of individuals in terms of gender, age, and experience. Because the sus-
pected contaminating factors are matched across the groups, we may take com-
fort in saying that variable X alone causes variable Y, if such is the result of the
study. But here, we are not sure that we have controlled all the nuisance factors,
since we may not be aware of them all. A safer bet is to randomize.

Randomization
Another way of controlling the contaminating variables is to assign the 60 mem-
bers randomly (i.e., with no predetermination) to the four groups. That is, every
member would have a known and equal chance of being assigned to any of these
four groups. For instance, we might throw the names of all the 60 members into
a hat, and draw their names. The first 15 names drawn may be assigned to the
first group, the second 15 to the second group, and so on, or the first person
drawn might be assigned to the first group, the second person drawn to the sec-
ond group, and so on. Thus, in randomization, the process by which individuals
are drawn (i.e., everybody has a known and equal chance of being drawn) and
their assignment to any particular group (each individual could be assigned to any
one of the groups set up) are both random. By thus randomly assigning members
to the groups we would be distributing the confounding variables among the
groups equally. That is, the variables of age, sex, and previous experience—the
controlled variables—will have an equal probability of being distributed among
the groups. The process of randomization would ideally ensure that each group
is comparable to the other, and that all variables, including the effects of age, sex
and previous experience are controlled. In other words, each of the groups will
have some members who have more experience mingled with those who have
less or no experience. All groups will have members of different age and sex com-
position. Thus randomization would ensure that if these variables do indeed have
a contributory or confounding effect, we would have controlled their confound-
ing effects (along with those of other unknown factors) by distributing them
across groups. This is achieved because when we manipulate the independent
variable of piece rates by having no piece rate system at all for one group (con-
trol) and having different piece rates for the other three groups (experimental),
we can determine the causal effects of the piece rates on production levels. Any
errors or biases caused by age, sex, and previous experience are now distributed