We now know that numbers can perform multiple jobs. Numbers can stand for
names or categories, or they can measure something, but something remarkable
happens when we put a lot of numbers together in a group. When you group
related numbers together, they become a variable. Variables are anything that can
vary or produce two or more different values. So if you think about any quality
of the human experience, it's probably a variable. How about age? If we ask a
randomly selected group of human beings about their age, would we get different
numbers or will they all be the same? Because age can take on more than one
value in a group, because age can vary, age is a variable. Well what else could
be a variable among human beings? Age, race, hair color, intelligence, gender,
anxiety, aggression, personality type, all of those can be measured, and all of them
would be variables. Now on the other hand, some groups of numbers can only assume
one value, they do not vary, and those are called constants. Now some values are
constant because they theoretically cannot vary. For instance, a cup of liquid
is eight ounces. The curb weight of a 1976 Ford Pinto is 2,595 pounds. The earth
goes around the Sun once every 24 hours. Other variables are constants because we
make them constants. For instance, I helped some researchers who were
studying post-operative outcomes in a maternity ward, so all of their patients
were female. In that study, gender was a constant. Or if you were studying the
income differences between men and women, we know that income is closely tied to
education. So if we were looking for income differences
based on gender, we should make sure that we are comparing men and women with
similar levels of education. In that case, we would hold education constant to
control for differences. Another way to describe variables is as quantitative or
qualitative. A quantitative variable indicates an amount. Quantitative
variables are expressed as a number, such as height in inches, test scores in point
totals, or weight in pounds. Quantitative variables quantify an amount. Qualitative
variables indicate a characteristic or quality of an individual. They cannot
convey an amount. Linguistic studies focus on word usage, such as positive or
negative content. Gender is a quality of an individual. You have a Type A or type
B personality, or maybe you are an ISTJ on the Myers-Briggs personality profile
or an "influencer" on the DiSC personality profile, or according to that personality
test on Facebook, your personality is most like Sheldon on the Big Bang Theory.
By the way those Facebook personality tests like what kind of dog are you? Are
all bogus and they only exist to collect personal information about you without
paying you so they can then use it to more effectively market stuff to you.
Just saying. Another way to describe variables is as categorical versus
continuous variables. A continuous variable allows for fractional amounts
or at least theoretically. Continuous variables would be scale variables,
interval or ratio level data, such as the passage of time, 6.4435 years, or
temperature, 98.6 degrees Fahrenheit, or IQ. Even though you can't get a 98.6
IQ, meaning that technically it is a discrete variable, theoretically IQ is
still continuous. A continuous scale is like a ramp. You can be any height from
the ground. If we have a ramp, I could say to you go stand so that you are 9 inches
above the sidewalk and you could scoot up and down the ramp to find the one
spot where your right foot was 9 inches off of the ground. A categorical variable
on the other hand can measure only whole number amounts. There cannot be partials
or fractions. Categorical variables are also called discrete variables. How many
cars do you own? How many children do you have? How many songs are on your iPod? How
many ipods do you own? Categorical scales are like a staircase. Unlike the ramp,
when you're standing on the stairs, you can only be six inches, 12 inches, 18
inches etc from the ground. There is no place on the stairs where you could
stand 9 inches off the ground, because the stairs are in categories of 6 inches
each. There's also a special case of categorical variable called dichotomous
variables. A dichotomous variable is a discrete variable that can have only two
values, no more no less. You can only be in one category. You can't be in both; you
can't be in neither. For instance, pass/fail on a test - you either passed or
you failed. You can't both pass and fail, you can't neither past nor fail. Or
living/dead. You're either one or the other. There's no such thing as being
mostly dead, versus all dead, even if miracle max said so in the princess
bride. Although if you were all dead, there was really only one thing we could
do, go through your pockets and look for loose change. Or pregnant not pregnant.
Again, it's a dichotomy. One or the other not
both, not neither, there is no such thing as being a little bit pregnant.