The Professor's Response

Hi Professor,

I am reviewing the examples on Chapter 8 and got stuck on something.

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Example 122: In a 2007 study of different popular diets, 77 people used a modified* version of the

Atkins Diet for one year. Their mean weight change was -10.34 lbs.

Assume that the population standard deviation for all such weight

changes is known to be 15.51 pounds. Use a significance level of

0.05 to test the claim that the mean weight change is equal to zero.

Does the diet seem to be effective? Does the mean weight change

seem substantial enough to justify the diet? What assumptions are

necessary for the test we just conducted to be valid?

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The claim is: m=0 but why is it the null hypothesis and not the alternative hypothesis? I assumed when we test a claim it's going to be the alternative hypothesis and the opposite would be the null.

See the professor's answer below.

Hi Lina,

The claim can be either the null or the alternative hypothesis. It all depends what symbol is used in the claim. If the claim features any kind of an equal sign (≥ , ≤, or =), it is the null hypothesis.

Professor McGuckian