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\(\mathbf{P}\) (Type II error) large when \(p\) close to \(\mathbf{H}_{0}\) For testing \(\mathrm{H}_{0}: p=1 / 3\) (astrologers randomly guessing) against \(\mathrm{H}_{a}: p>1 / 3\) with \(n=116,\) Example 13 showed that \(\mathrm{P}(\) Type II error \()=0.02\) when \(p=0.50 .\) Now suppose that \(p=0.35\). Recall that \(\mathrm{P}\) (Type I error) \(=0.05\). a. Show that \(\mathrm{P}\) (Type II error) \(=0.89\). b. Explain intuitively why P(Type II error) is large when the parameter value is close to the value in \(\mathrm{H}_{0}\) and decreases as it moves farther from that value.

Short Answer

Expert verified
a. \(\mathrm{P}( ext{Type II error}) = 0.89\). b. Type II error is large when \(p\) is close to \(H_0\) because the difference is subtler, making it harder to detect.

Step by step solution

01

Understand the Hypotheses

We are testing the null hypothesis \(H_0: p = \frac{1}{3}\) against the alternative hypothesis \(H_a: p > \frac{1}{3}\). Here, \(p\) is the true probability we are trying to estimate.
02

Define Type I and Type II Errors

A Type I error occurs when we reject \(H_0\) when it is true, and its probability is given as \(\alpha = 0.05\). A Type II error occurs when we accept \(H_0\) when \(H_a\) is true; this probability is denoted as \(\beta\).
03

Set the Significance Level and Test Statistic

The significance level \(\alpha = 0.05\) suggests the critical value for the test statistic. We use a normal approximation since \(n=116\) is large enough. The critical region compares sample proportions to a critical value from the standard normal distribution.
04

Calculate the Test Statistic for \(p = 0.35\)

Find the z-value for the given test stat. Given \(H_0\), calculate the standard deviation of the sampling distribution, \(\sigma = \sqrt{\frac{1}{3}(1-\frac{1}{3})/116}\). The z-value when \(p=0.35\) is found by \((0.35 - \frac{1}{3})/\sigma\).
05

Find \(\mathrm{P}( ext{Type II error})\) using \(\beta\) Calculation

The probability of making a Type II error is the probability that the calculated test statistic is less than the critical z-value of 1.645 for \(p = 0.35\). Use the standard normal distribution to find this probability.
06

Explain Intuition Behind Type II Error Probability

The closer \(p\) is to \(H_0\), the tougher it is to detect a difference, making \(\beta\) (Type II error) higher. As \(p\) deviates further from \(H_0\), this difference becomes easier to detect, reducing \(\beta\).

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Key Concepts

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

Type II Error
A Type II error occurs when we fail to reject the null hypothesis when the alternative hypothesis is actually true. In simpler terms, it's like sounding the all-clear when there's still a risk. Imagine a doctor telling a patient they are completely healthy when they're not; that's akin to a Type II error in statistical testing. This error is represented by the symbol \( \beta \).

The probability of a Type II error increases when the actual value of \( p \) is close to the null hypothesis value. Thus, if \( p = 0.35 \) and our null hypothesis \( H_0 \) asserts \( p = 1/3 \), it's challenging to distinguish between these close values, leading to a higher chance of making a Type II error. However, as the true value of \( p \) moves away from \( H_0 \), it becomes simpler to detect this deviation, and thus the probability of making this error declines.

In this context, finding \( \beta = 0.89 \) when \( p = 0.35 \) means there's an 89% chance of a Type II error, indicating how tough it is to spot the slight difference when \( p \) is close to \( H_0 \).
Significance Level
The significance level, denoted as \( \alpha \), is the threshold at which we decide whether to reject the null hypothesis. In hypothesis testing, it reflects the probability of making a Type I error, which occurs when we reject the null hypothesis \( H_0 \) when it is actually true—like believing a false alarm.

For the given exercise, \( \alpha \) is set at 0.05. This means we accept a 5% risk of incorrectly rejecting \( H_0 \). It acts as the cut-off point in deciding if our test results are statistically significant. If the calculated test statistic falls into the critical region determined by this significance level, we reject \( H_0 \). Otherwise, we fail to reject it.

Choosing a smaller \( \alpha \) reduces the chances of a Type I error but potentially increases the probability of a Type II error, and vice versa. Researchers must carefully determine the significance level based on the context of their study and the consequences of making errors.
Normal Approximation
When conducting hypothesis tests, especially with a large sample size, it is common to use a normal approximation to model the sampling distribution of a proportion. This is due to the Central Limit Theorem, which suggests that, for large enough \( n \), the distribution of sample means will be approximately normal, regardless of the distribution of the population.

In the given exercise, the sample size \( n = 116 \) is sufficiently large, allowing us to apply this approximation effectively. This aids in converting the discrete distribution of sample proportions into a continuous normal distribution, making it easier to calculate probabilities and critical values using standard normal tables.

The standard deviation of the sampling distribution is computed using the formula \( \sigma = \sqrt{\frac{p(1-p)}{n}} \), which helps in defining the z-value or test statistic. This transformation enables the use of a standard normal distribution (or z-distribution) to assess the test statistics derived from the sample data.
Test Statistic
A test statistic is a standardized value calculated from sample data during a hypothesis test. It enables us to decide between the null and alternative hypotheses. Essentially, it measures how far the sample data diverges from what is expected under the null hypothesis.

In this exercise, we compute a z-value as the test statistic. The z-value is calculated using the formula: \[ z = \frac{\hat{p} - p_0}{\sigma} \] where \( \hat{p} \) is the sample proportion, \( p_0 \) is the hypothesized proportion under \( H_0 \), and \( \sigma \) is the standard deviation of the sampling distribution.

The test statistic is then compared to a critical value from the standard normal distribution. For a significance level \( \alpha = 0.05 \), a one-tailed test would use a critical value of approximately 1.645. If the test statistic exceeds this critical value, we reject the null hypothesis. This methodology helps determine whether the observed effect is significant or could have occurred by random chance, guiding decision-making in statistics.

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Most popular questions from this chapter

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