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If a \(90 \%\) confidence interval for the difference of means \(\mu_{1}-\mu_{2}\) contains all positive values, what can we conclude about the relationship between \(\mu_{1}\) and \(\mu_{2}\) at the \(90 \%\) confidence level?

Short Answer

Expert verified
At the 90% confidence level, \( \mu_{1} \) is likely greater than \( \mu_{2} \).

Step by step solution

01

Understanding Confidence Interval

A confidence interval provides a range of values which is likely to contain the parameter of interest. A 90% confidence interval means that we are 90% confident that the true parameter lies within this interval.
02

Analyzing the Given Interval

The problem states that the 90% confidence interval for the difference of means \( \mu_{1} - \mu_{2} \) contains all positive values. This indicates that when you subtract \( \mu_{2} \) from \( \mu_{1} \), the results are always greater than zero.
03

Interpreting Positive Differences

If \( \mu_{1} - \mu_{2} \) is always positive within the interval, this suggests that \( \mu_{1} \) is greater than \( \mu_{2} \) for the entire confidence interval range.
04

Conclusion About Means

Since the entire interval for \( \mu_{1} - \mu_{2} \) is positive, at a 90% confidence level we can conclude that \( \mu_{1} \) is likely greater than \( \mu_{2} \).

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Key Concepts

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

Statistical Inference
Statistical inference is like a detective's tool for understanding data. It's about making educated guesses or conclusions from data samples, telling you more about larger populations. This process involves using some probability to draw conclusions, which means these conclusions aren't always 100% certain but are based on evidence.

Confidence intervals are a key aspect of statistical inference. They give a way of marking out a range where we believe our true parameter likely lies. For example, when we talk about a 90% confidence interval, we're saying that if we repeated the sampling process numerous times, around 90% of those intervals would capture the actual parameter. This doesn't mean that there's a 90% chance the parameter is in the interval; rather, it describes the process's reliability.
  • Helps make predictions or decisions based on data.
  • Allows for the estimation of population parameters.
  • Utilizes sampling to infer characteristics of a larger group.
Understanding statistical inference means embracing uncertainty, but using probability to make valid conclusions nonetheless. It's a way of making informed decisions based on what the data indicates.
Difference of Means
The difference of means refers to the subtraction of one population mean from another. It's an essential statistical concept when comparing two groups. Imagine you want to compare the average heights of plants grown in sunlight vs. shade; the difference of means allows you to see this difference in a numerical way.

In statistical analysis, we often use confidence intervals to understand this difference better. If a confidence interval for the difference of means contains only positive values, it suggests one group mean (let's say sunlight) is consistently higher than the other (shade).
  • Helps in comparing two different groups.
  • Can show if one group is genuinely different from another in terms of a specific measure.
  • Used widely in hypothesis testing to understand contrasts between groups.
Knowing about the difference of means can help us determine relationships and effects between different populations.
Parameter Estimation
Parameter estimation involves deducing the values of parameters (like means, variances) in a statistical model. It's essentially guesswork but informed and mathematical. Using sample data, we estimate the parameters of a larger population. This is where confidence intervals play a critical role.

When we estimate the parameters using confidence intervals, we don’t point to one exact number but rather a range of plausible values. For example, when assessing the difference between two means, parameter estimation helps not just to estimate the difference but to say with a certain level of confidence how big that difference really is.
  • It’s the process of determining the values of population parameters.
  • Helps provide a range within which we expect the true parameter to fall.
  • Gives a measure of reliability to statistical results.
Understanding parameter estimation is crucial as it allows us to translate our data into practical insights and decisions.

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Most popular questions from this chapter

Confidence Interval for \(\mu_{1}-\mu_{2}\) Consider two independent normal distributions. A random sample of size \(n_{1}=20\) from the first distribution showed \(\bar{x}_{1}=12\) and a random sample of size \(n_{2}=25\) from the second distribution showed \(\bar{x}_{2}=14\). (a) Check Requirements If \(\sigma_{1}\) and \(\sigma_{2}\) are known, what distribution does \(\bar{x}_{1}-\bar{x}_{2}\) follow? Explain. (b) Given \(\sigma_{1}=3\) and \(\sigma_{2}=4\), find a \(90 \%\) confidence interval for \(\mu_{1}-\mu_{2}\) (c) Check Requirements Suppose \(\sigma_{1}\) and \(\sigma_{2}\) are both unknown, but from the random samples, you know \(s_{1}=3\) and \(s_{2}=4 .\) What distribution approximates the \(\bar{x}_{1}-\bar{x}_{2}\) distribution? What are the degrees of freedom? Explain. (d) With \(s_{1}=3\) and \(s_{2}=4\), find a \(90 \%\) confidence interval for \(\mu_{1}-\mu_{2} .\) (e) If you have an appropriate calculator or computer software, find a \(90 \%\) confidence interval for \(\mu_{1}-\mu_{2}\) using degrees of freedom based on Satterthwaite's approximation. (f) Interpretation Based on the confidence intervals you computed, can you be \(90 \%\) confident that \(\mu_{1}\) is smaller than \(\mu_{2}\) ? Explain.

Assume that the population of \(x\) values has an approximately normal distribution. Camping: Cost of a Sleeping Bag How much does a sleeping bag cost? Let's say you want a sleeping bag that should keep you warm in temperatures from \(20^{\circ} \mathrm{F}\) to \(45^{\circ} \mathrm{F}\). A random sample of prices (\$) for sleeping bags in this temperature range was taken from Backpacker Magazine: Gear Guide (Vol. 25, Issue 157 , No. 2). Brand names include American Camper, Cabela's, Camp 7, Caribou, Cascade, and Coleman. $$ \begin{array}{rrrrrrrrrr} 80 & 90 & 100 & 120 & 75 & 37 & 30 & 23 & 100 & 110 \\ 105 & 95 & 105 & 60 & 110 & 120 & 95 & 90 & 60 & 70 \end{array} $$ (a) Use a calculator with mean and sample standard deviation keys to verify that \(\bar{x} \approx \$ 83.75\) and \(s \approx \$ 28.97\). (b) Using the given data as representative of the population of prices of all summer sleeping bags, find a \(90 \%\) confidence interval for the mean price \(\mu\) of all summer sleeping bags. (c) Interpretation What does the confidence interval mean in the context of this problem?

Sam computed a \(90 \%\) confidence interval for \(\mu\) from a specific random sample of size \(n .\) He claims that at the \(90 \%\) confidence level, his confidence interval contains \(\mu\). Is his claim correct? Explain.

Myers-Briggs: Marriage Counseling Isabel Myers was a pioneer in the study of personality types. She identified four basic personality preferences, which are described at length in the book A Guide to the Development and Use of the Myers-Briggs Type Indicator by Myers and McCaulley (Consulting Psychologists Press). Marriage counselors know that couples who have none of the four preferences in common may have a stormy marriage. Myers took a random sample of 375 married couples and found that 289 had two or more personality preferences in common. In another random sample of 571 married couples, it was found that only 23 had no preferences in common. Let \(p_{1}\) be the population proportion of all married couples who have two or more personality preferences in common. Let \(p_{2}\) be the population proportion of all married couples who have no personality perferences in common. (a) Check Requirements Can a normal distribution be used to approximate the \(\hat{p}_{1}-\hat{p}_{2}\) distribution? Explain. (b) Find a \(99 \%\) confidence interval for \(p_{1}-p_{2}\). (c) Interpretation Explain the meaning of the confidence interval in part (a) in the context of this problem. Does the confidence interval contain all positive, all negative, or both positive and negative numbers? What does this tell you (at the \(99 \%\) confidence level) about the proportion of married couples with two or more personality preferences in common compared with the proportion of married couples sharing no personality preferences in common?

Ballooning: Air Temperature How hot is the air in the top (crown) of a hot air balloon? Information from Ballooning: The Complete Guide to Riding the Winds by Wirth and Young (Random House) claims that the air in the crown should be an average of \(100^{\circ} \mathrm{C}\) for a balloon to be in a state of equilibrium. However, the temperature does not need to be exactly \(100^{\circ} \mathrm{C}\). What is a reasonable and safe range of temperatures? This range may vary with the size and \((\mathrm{dec}-\) orative) shape of the balloon. All balloons have a temperature gauge in the crown. Suppose that 56 readings (for a balloon in equilibrium) gave a mean temperature of \(\bar{x}=97^{\circ} \mathrm{C}\). For this balloon, \(\sigma \approx 17^{\circ} \mathrm{C}\). (a) Compute a \(95 \%\) confidence interval for the average temperature at which this balloon will be in a steady-state equilibrium. (b) Interpretation If the average temperature in the crown of the balloon goes above the high end of your confidence interval, do you expect that the balloon will go up or down? Explain.

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