Page 62 - Statistics for Dummies

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Part I: Vital Statistics about Statistics
data they gave me are the following: 0, 2, 1, 4, 18. (The fifth friend counted
each of her aquarium fish as a separate pet.) Not all data are numbers; I also
recorded the gender of each of my friends, giving me the following data:
male, male, female, male, female.
Most data fall into one of two groups: numerical or categorical. (I present the
main ideas about these variables here; see Chapter 5 for more details.)
✓ Numerical data: These data have meaning as a measurement, such as a
person’s height, weight, IQ, or blood pressure; or they’re a count, such
as the number of stock shares a person owns, how many teeth a dog
has, or how many pages you can read of your favorite book before you
fall asleep. (Statisticians also call numerical data quantitative data.)

Numerical data can be further broken into two types: discrete and
continuous.
• Discrete data represent items that can be counted; they take on
possible values that can be listed out. The list of possible values
may be fixed (also called finite); or it may go from 0, 1, 2, on to
infinity (making it countably infinite). For example, the number of
heads in 100 coin flips takes on values from 0 through 100 (finite
case), but the number of flips needed to get 100 heads takes on
values from 100 (the fastest scenario) on up to infinity. Its possible
values are listed as 100, 101, 102, 103, . . . (representing the count-
ably infinite case).
• Continuous data represent measurements; their possible values
cannot be counted and can only be described using intervals on
the real number line. For example, the exact amount of gas pur-
chased at the pump for cars with 20-gallon tanks represents nearly-
continuous data from 0.00 gallons to 20.00 gallons, represented by
the interval [0, 20], inclusive. (Okay, you can count all these values,
but why would you want to? In cases like these, statisticians bend
the definition of continuous a wee bit.) The lifetime of a C battery
can be anywhere from 0 to infinity, technically, with all possible
values in between. Granted, you don’t expect a battery to last more
than a few hundred hours, but no one can put a cap on how long it
can go (remember the Energizer Bunny?).
✓ Categorical data: Categorical data represent characteristics such as a
person’s gender, marital status, hometown, or the types of movies they
like. Categorical data can take on numerical values (such as “1” indicating
male and “2” indicating female), but those numbers don’t have meaning.
You couldn’t add them together, for example. (Other names for categori-
cal data are qualitative data, or Yes/No data.)

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