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Stat Tutor

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0:48

Correct. We have evidence against the null hypothesis whenever *P*-value is smaller than α.

Incorrect. We have evidence against the null hypothesis whenever *P*-value is smaller than α.

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1:54

Correct. A skeptical doctor wants strong evidence for St. John’s Wort so would set α very small, like 0.01.

Incorrect. A skeptical doctor wants strong evidence for St. John’s Wort so would set α very small, like 0.01.

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2:58

Correct. If the consequences of rejecting a correct null hypothesis are very serious, set α very small, like 0.01.

Incorrect. If the consequences of rejecting a correct null hypothesis are very serious, set α very small, like 0.01.

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Correct. If the consequences of failing to reject an incorrect null hypothesis are very serious, set α on the large side, like 0.10.

Incorrect. If the consequences of failing to reject an incorrect null hypothesis are very serious, set α on the large side, like 0.10.

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3:56

Correct. If chlorine is not added when it should be, you increase the risk of spreading disease.

Incorrect. If chlorine is not added when it should be, you increase the risk of spreading disease.

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Correct. If chlorine is added when it shouldn't be, you increase the risk of skin irritation.

Incorrect. If chlorine is added when it shouldn't be, you increase the risk of skin irritation.

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Correct. This is a subjective question. Most would agree that “not adding chlorine when you should” is the most serious consequence.

Incorrect. This is a subjective question. Most would agree that “not adding chlorine when you should” is the most serious consequence.

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4:38

Correct. Selecting α of 0.01 leads us to reject H_{0} less often which lessens the risk of skin irritation, but increases the risk of disease. Selecting α of 0.10 leads us to reject H_{0} more often and add chlorine more often than perhaps we need to. This lessens the risk of disease, but increases the risk of skin irritation.

Incorrect. Selecting α of 0.01 leads us to reject H_{0} less often which lessens the risk of skin irritation, but increases the risk of disease. Selecting α of 0.10 leads us to reject H_{0} more often and add chlorine more often than perhaps we need to. This lessens the risk of disease, but increases the risk of skin irritation.

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6:32

Correct. Since *P*-value = 0.049 < α = 0.05, we reject H_{0}.

Incorrect. Since *P*-value = 0.049 < α = 0.05, we reject H_{0}.

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Correct. Since *P*-value = 0.051 < α = 0.05, we fail to reject H_{0}.

Incorrect. Since *P*-value = 0.051 < α = 0.05, we fail to reject H_{0}.

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Correct. α should be used as a guide for rejecting and failing to reject H_{0}.

Incorrect. α should be used as a guide for rejecting and failing to reject H_{0}.

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7:28

Correct. This is true because *P*-value for a two-sided test is the area in both tails whereas *P*-value for a one-sided test is the area in only one tail.

Incorrect. This is true because *P*-value for a two-sided test is the area in both tails whereas *P*-value for a one-sided test is the area in only one tail.

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9:16

Correct. As \(\overline{x}\) gets farther and farther from \(\mu _{0} \), *P*-value gets smaller and smaller because the tail area gets smaller and smaller.

Incorrect. As \(\overline{x}\) gets farther and farther from \(\mu _{0} \), *P*-value gets smaller and smaller because the tail area gets smaller and smaller.

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Correct. If sample size is too small, \( \frac{ \sigma }{ \sqrt{n} } \) may be so large that the difference \(\overline{x} - \mu _{0} \) does not have a small *P*-value when H_{0} is incorrect and thus is not declared to be statistically significant.

Incorrect. If sample size is too small, \( \frac{ \sigma }{ \sqrt{n} } \) may be so large that the difference \(\overline{x} - \mu _{0} \) does not have a small *P*-value when H_{0} is incorrect and thus is not declared to be statistically significant.

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9:46

Correct. Check for practical significance whenever sample size is really large.

Incorrect. Check for practical significance whenever sample size is really large.

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10:39

Correct. Since *P*-value = 0.0004 < α = 0.05, these results are statistically significant.

Incorrect. Since *P*-value = 0.0004 < α = 0.05, these results are statistically significant.

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11:02

Correct. Statistical significance and practical significance are not the same.

Incorrect. Statistical significance and practical significance are not the same.

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11:34

Correct. A one point difference is not worth investing time and money to improve the average score of rural students.

Incorrect. A one point difference is not worth investing time and money to improve the average score of rural students.

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13:32

Correct. A difference that is not big enough to matter is not practically significant.

Incorrect. A difference that is not big enough to matter is not practically significant.

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14:30

Correct. For statistical significance, check to see if *P*-value is smaller than α.

Incorrect. For statistical significance, check to see if *P*-value is smaller than α.

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Correct. For practical significance, check to see if the difference \(\overline{x} - \mu _{0} \) is big enough to matter.

Incorrect. For practical significance, check to see if the difference \(\overline{x} - \mu _{0} \) is big enough to matter.

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15:34

Correct. This is exactly what we mean by “multiple analyses.”

Incorrect. This is exactly what we mean by “multiple analyses.”

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19:55

Correct. When performing multiple analyses, more than one null hypothesis is tested using the same data. Since they are all tested using the same data, more of these get rejected than should be.

Incorrect. When performing multiple analyses, more than one null hypothesis is tested using the same data. Since they are all tested using the same data, more of these get rejected than should be.

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22:06

Correct. When the sample size is very large, a difference may be declared as statistically significant when it is not practically significant.

Incorrect. When the sample size is very large, a difference may be declared as statistically significant when it is not practically significant.

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Correct. The sample size may be too small to detect real differences.

Incorrect. The sample size may be too small to detect real differences.

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