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Exercise 11.32 showed the association between recreation and happiness. The table shown here gives the standardized residuals for those data in parentheses. a. Explain what a relatively small standardized residual such as -0.5 in the second cell represents. b. Identify the cells in which you would infer that the population has more cases than would occur if recreation and happiness were independent. Pick one of these cells and explain the association relative to independence.

Short Answer

Expert verified
A standardized residual of -0.5 indicates a minor deviation from expected frequency. Cells with large positive residuals indicate more cases than expected under independence, showing a strong association.

Step by step solution

01

Understand the Role of Standardized Residuals

Standardized residuals are used in a chi-square test to measure the degree to which observed frequencies differ from expected frequencies for each cell. A standardized residual close to 0 indicates little difference between observed and expected counts, suggesting the observed data roughly fit the expected model of independence. Conversely, large positive or negative residuals indicate significant deviations.
02

Interpret a Small Standardized Residual

A small standardized residual like -0.5 suggests that there is not much difference between the observed frequency and the expected frequency under the assumption of independence. Specifically, the cell with a residual of -0.5 shows that the observed frequency is slightly less than expected, but it's not a significant deviation from independence.
03

Identify Cells with Higher Observed Cases

Look for cells with large positive standardized residuals, as these indicate cells where the observed frequency is higher than expected. More than one standard deviation from zero typically suggests that there's more going on than pure chance, indicating a significant association.
04

Choose a Cell and Explain

Suppose we identify a cell with a standardized residual of, say, +2. This indicates more participants in that category than would be expected if recreation and happiness were independent, suggesting a positive association between recreation in that category and happiness levels. The deviation implies that the relationship between recreation and happiness for that group is stronger than expected.

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Key Concepts

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

Standardized Residuals
In a chi-square test, standardized residuals help us understand the relationship between observed frequencies and expected frequencies in a dataset. They show how much an observation in a cell deviates from what we would expect if there was no association. Standardized residuals can be thought of as measurements of how unusual a cell's data is, compared to what the model of no interaction predicts.

When a residual is close to 0, it means the data is pretty much what you'd expect if the variables were independent. This implies there's little to no evidence for any association. If the cell's data fits well with the independence model, we won't see many red flags in our standardized residual analysis for that spot.

However, when these residuals are larger either positively or negatively, they suggest that there might be more at play than merely random chance. A large positive residual indicates that there are more occurrences than expected, whereas a large negative residual shows fewer occurrences than expected. This difference can help identify the particular cells contributing most to any detected association, leading us to further hypothesis testing.
Association Analysis
Association analysis in statistics is a significant tool used to examine the relationship between two categorical variables. In the scenario of recreation and happiness, for instance, it aims to understand how these two aspects affect one another. The chi-square test is often utilized for association analysis.

In practice, association analysis involves looking at the chi-square statistic to evaluate the likelihood that any observed relationship is due to chance. If the chi-square statistic is significant, this suggests that there is a meaningful connection between the two measured factors.

A crucial part of association analysis is interpreting standardized residuals which offer a deeper insight into specific areas of the dataset. They identify where exactly the deviations from expected independence are occurring by highlighting those cells that have more or fewer cases than anticipated. This method pinpoints the strength and direction of an association in the context of a bigger picture.
Independence in Statistics
The concept of independence in statistics refers to the idea that two variables are independent if the occurrence or change in one does not affect the occurrence or change in the other. For instance, if recreation and happiness are independent, then knowing someone's level of recreation doesn't help you predict their happiness level, and vice versa.

In statistical testing, especially with chi-square tests, independence serves as the null hypothesis. We gauge whether we should reject this hypothesis by comparing observed data with what we would expect if the variables were independent.

Evaluating independence often employs calculations of expected frequencies, which are then compared against the actual observed data within contingencies. If significant differences are noticed, with standardized residuals flagging certain cells for their deviation, independence might be discounted in favor of a model suggesting some degree of association.

Understanding independence is crucial as it lays the groundwork for testing hypotheses about the relationships between variables, helping us discern whether the linkages are statistically significant or just a product of random variation.

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Most popular questions from this chapter

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A study used 1496 patients suffering from low levels of anxiety. The study randomly assigned each subject to a cognitive behavioral therapy (CBT) treatment or a placebo treatment. In this study, increased anxiety levels were observed for 45 of the 729 subjects taking a placebo and for 29 of the 767 subjects taking CBT. a. Report the data in the form of a \(2 \times 2\) contingency table. b. Show how to carry out all five steps of the null hypothesis that having an anxiety attack is not associated with whether one is taking a placebo or CBT. (You should get a chi-squared statistic equal to \(4.5 .\) ) Interpret.

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