Page 56 - Statistics for Dummies

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Part I: Vital Statistics about Statistics
Many surveys are based on large numbers of participants, but that isn’t
always true for other types of research, such as carefully controlled experi-
ments. Because of the high cost of some types of research in terms of time
and money, some studies are based on a small number of participants or
products. Researchers have to find the appropriate balance when determin-
ing sample size.
The most unreliable results are those based on anecdotes, stories that talk
about a single incident in an attempt to sway opinion. Have you ever told some-
one not to buy a product because you had a bad experience with it? Remember
that an anecdote (or story) is really a nonrandom sample whose size is only one.
Considering cause and effect
Headlines often simplify or skew the “real” information, especially when the
stories involve statistics and the studies that generated the statistics.
A study conducted a few years back evaluated videotaped sessions of 1,265
patient appointments with 59 primary-care physicians and 6 surgeons in
Colorado and Oregon. This study found that physicians who had not been
sued for malpractice spent an average of 18 minutes with each patient,
compared to 16 minutes for physicians who had been sued for malpractice.
The study was reported by the media with the headline, “Bedside manner
fends off malpractice suits.” However, this study seemed to say that if you
are a doctor who gets sued, all you have to do is spend more time with your
patients, and you’re off the hook. (Now when did bedside manner get charac-
terized as time spent?)
Beyond that, are we supposed to believe that a doctor who has been sued
needs only add a couple more minutes of time with each patient to avoid
being sued in the future? Maybe what the doctor does during that time
counts much more than how much time the doctor actually spends with
each patient. You tackle the issues of cause-and-effect relationships between
variables in Chapter 18.
Finding what you wanted to find
You may wonder how two political candidates can discuss the same topic
and get two opposing conclusions, both based on “scientific surveys.” Even
small differences in a survey can create big differences in results. (See
Chapter 16 for the full scoop on surveys.)
One common source of skewed survey results comes from question wording.
Here are three different questions that are trying to get at the same issue —
public opinion regarding the line-item veto option available to the president:

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