# Answers to the checkpoints of chapter 6

Checkpoint 1

• If there are differences between the sample and test value, and if the sample has a normal distribution.
• The hypothesis is that the age is lower, so the hypothesis has a direction.
• The null hypothesis is not rejected (p value = 0.0668; conclusion p > 0.005).

Checkpoint 2

• You would use a t test if the population variance is not known and (in some cases) for small samples.
• From 120 onwards, the shape of the t distribution is the same as a normal distribution.
• A critical value is the t value or the z value associated with the chosen significance level.

Checkpoint 3

• If you have two dependent groups and the population variance is unknown.
• Because there is an association in the data that has been collected.
• No.

Checkpoint 4

• In terms of whether the population variance is known or not known.
• From n = 120 onwards.
• That is a test in which the groups being compared have the same variance.
• At df = 199, the critical t value is 1.96; if you perform a z test, the critical value is also 1.96, because the sample for this is sufficiently large.

Checkpoint 5

• No, you don’t reject it; p = 0.06.
• Yes, at 5% with a one-tailed test, you would.

Checkpoint 6

• You could adjust the degrees of freedom.
• You have made a Type I error.
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