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Part IV: Guesstimating and Hypothesizing with Confidence
2. Collect good data using a well-designed study (see Chapters 16 and 17).

3. Calculate the test statistic based on your data.

4. Find the p-value for your test statistic.

5. Decide whether or not to reject H based on your p-value.
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6. Understand that your conclusion may be wrong, just by chance.
Setting Up the Hypotheses
Typically in a hypothesis test, the claim being made is about a population
parameter (one number that characterizes the entire population). Because
parameters tend to be unknown quantities, everyone wants to make claims
about what their values may be. For example, the claim that 25% (or 0.25)
of all women have varicose veins is a claim about the proportion (that’s the
parameter) of all women (that’s the population) who have varicose veins
(that’s the variable — having or not having varicose veins).
Researchers often challenge claims about population parameters. You may
hypothesize, for example, that the actual proportion of women who have
varicose veins is lower than 0.25, based on your observations. Or you may
hypothesize that due to the popularity of high heeled shoes, the proportion
may be higher than 0.25. Or if you’re simply questioning whether the actual
proportion is 0.25, your alternative hypothesis is: “No, it isn’t 0.25.”
Defining the null
Every hypothesis test contains a set of two opposing statements, or hypoth-
eses, about a population parameter. The first hypothesis is called the null
hypothesis, denoted H . The null hypothesis always states that the population
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parameter is equal to the claimed value. For example, if the claim is that the
average time to make a name-brand ready-mix pie is five minutes, the statisti-
cal shorthand notation for the null hypothesis in this case would be as fol-
lows: H : μ = 5. (That is, the population mean is 5 minutes.)
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All null hypotheses include an equal sign in them; there are no ≤ or ≥ signs in
H . Not to cop out or anything, but the reason it’s always equal is beyond the
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scope of this book; let’s just say you wouldn’t pay me to explain it to you.

What’s the alternative?
Before actually conducting a hypothesis test, you have to put two possible
hypotheses on the table — the null hypothesis is one of them. But, if the

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