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91Ó°ÊÓ

Rolling Dice You roll a die 60 times and record the sample proportion of fives, and you want to test whether the die is biased to give more fives than a fair die would ordinarily give. To find the p-value for your sample data, you create a randomization distribution of proportions of fives in many simulated samples of size 60 with a fair die. (a) State the null and alternative hypotheses. (b) Where will the center of the distribution be? Why? (c) Give an example of a sample proportion for which the number of 5 's obtained is less than what you would expect in a fair die. (d) Will your answer to part (c) lie on the left or the right of the center of the randomization distribution? (e) To find the p-value for your answer to part (c), would you look at the left, right, or both tails? (f) For your answer in part (c), can you say anything about the size of the p-value?

Short Answer

Expert verified
The null hypothesis is that probability of rolling a 5 is 1/6 and the alternative hypothesis is that the probability is more than 1/6. A fair die roll should result in center of the distribution being 1/6. A sample proportion may be 7/60, which is to the left of the center. The p-value is looked using the right tail, and likely will be rather large given the sample data not supporting strongly the alternative hypothesis.

Step by step solution

01

Formulate Hypotheses

The null hypothesis \(H_0\) is that the die is fair, meaning the probability of rolling a 5 is 1/6. The alternative hypothesis \(H_{a}\) is that the die is biased, meaning the probability of rolling a 5 is greater than 1/6.
02

Identify Center of the Distribution

The center of the distribution is expected to be at the proportion of 1/6 since the die is assumed fair under the null hypothesis. In 60 rolls, a fair die would produce 10 fives in average. Thus, the center of the distribution should be 10/60 = 1/6.
03

Sample Proportion Less than Expected

An example would be if we rolled a 5 seven times out of 60 rolls. The proportion is then 7/60 which is less than 1/6 (~0.167). This proportion is an example of a result less than that expected from a fair die.
04

Determine Position in Distribution

Since 7/60 is less than the center 1/6, this proportion would lie to the left of the center of the distribution.
05

Identify p-value Tail

Since we're testing if the die is biased to give more 5's (not less), therefore the p-value is found by looking at the right tail of the distribution.
06

Estimate Size of p-value

Given the alternative hypothesis and the location of our sample, we're likely to get a large p-value because getting 7/60 when the null hypothesis suggests 10/60 does not provide strong evidence against the null hypothesis.Technically speaking, p-value will depend on the standard deviation of the distribution, but it's reasonable to say the p-value will not be small considering our data is not in the extreme right tail - we do not have clear evidence against the null hypothesis.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Randomization Distribution
Understanding randomization distribution is key to hypothesis testing. It helps us visualize what sample results would look like under the assumption that the null hypothesis is true.
For the dice-rolling scenario, consider conducting numerous similar experiments: rolling a die 60 times and counting the number of fives.
- **Simulated Samples**: By simulating this process repeatedly, we can build a picture, or distribution, of possible results if the die were fair. - **Assumptions**: Each simulated sample assumes that the die is fair, producing what we expect to see naturally when we roll a fair die 60 times. - **Purpose**: Randomization distribution gives us a benchmark for comparison. We compare our actual results to see how likely they are under these fair-die assumptions.
In practical terms, this is like creating a histogram of results from fair die rolls. The center of this distribution will naturally sit around 1/6, since that's what we expect for a fair six-sided die.
P-value
The concept of a p-value is central to making decisions in hypothesis testing.
It helps to measure the evidence against the null hypothesis. - **Definition**: A p-value represents the probability of observing a result as extreme, or more extreme, than what we actually observed, assuming that the null hypothesis is true. - **Interpretation**: A small p-value indicates that the observed result is unlikely under the null hypothesis, suggesting that perhaps the null hypothesis should be reconsidered. - **Current Example**: When testing whether the die is biased, if our result was a sample of 5s more frequent than expected, the p-value would tell us how probable such a result is under the assumption of a fair die. In our dice rolling example, looking at a right tail helps us see how often we would get the actual or even more extreme results, thus guiding us to understand if our p-value is significant.
Null Hypothesis
The null hypothesis is a statement that there is no effect or no difference; it's our starting assumption.
In this case, the null hypothesis argues that the die is fair.- **Symbol**: It's denoted as \(H_0\).- **Example Statement**: For this scenario, that would mean the probability of rolling a 5 on the die is exactly \(\frac{1}{6}\).- **Goal**: It's what we're testing against. In this dice example, we're performing the experiment to see if we can gather enough evidence to reject \(H_0\).Most of the time, the null hypothesis is embraced unless the evidence strongly suggests otherwise. It serves as a contrast to our alternative hypothesis.
Alternative Hypothesis
The alternative hypothesis is the claim that we're testing for, typically suggesting some measured effect or difference.
In this exercise, it hints that the die may be biased.- **Symbol**: It's usually referred to as \(H_a\) or \(H_1\).- **Example Statement**: Here, the alternative hypothesis posits that the probability of rolling a 5 is greater than \(\frac{1}{6}\).- **Relevance**: It gives direction to our hypothesis test. Particularly in the dice rolling example, we're checking if there are significantly more fives than a fair die would produce.The alternative hypothesis directly contrasts with the null hypothesis and is embraced if the evidence strongly suggests the null hypothesis is unlikely. Therefore, finding enough evidence to support \(H_a\) is key in hypothesis testing.

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