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A random sample of \(n=347\) students was selected, and each one was asked to complete several questionnaires, from which a Coping Humor Scale value \(x\) and a Depression Scale value \(y\) were determined. The resulting value of the sample correlation coefficient was \(-.18\). a. The investigators reported that \(P\) -value \(<.05 .\) Do you agree? b. Is the sign of \(r\) consistent with your intuition? Explain. (Higher scale values correspond to more developed sense of humor and greater extent of depression.) c. Would the simple linear regression model give accurate predictions? Why or why not?

Short Answer

Expert verified
a. Yes, agreement with the reported P-value is plausible. b. Yes, the negative sign of 'r' is consistent with the assumption that a better sense of humor is associated with a lower extent of depression. c. No, the simple linear regression model may not give accurate predictions due to the weak relationship (-.18) between the variables.

Step by step solution

01

Understanding P-value

The P-value is a statistical term that represents the statistical significance of the obtained results. It basically tells us if the result we got is due to chance or not. In this case, if P-value < .05, it means there exists a significant relationship between the two variables (Coping Humor Scale and Depression Scale), even though it's weak (as indicated by the correlation coefficient of -.18). Or in other words, the likelihood that the observed correlation occurred by chance is less than 5%. So, yes, as per definition, agreement with the investigator's report is plausible.
02

Understanding the correlation coefficient sign

The sign of the correlation coefficient ('r') can be positive or negative, and this indicates the direction of the relationship between the two variables. In this case, a negative correlation coefficient suggests that as the coping humor scale value increases (better sense of humor), the depression scale decreases (lesser extent of depression). This is consistent with intuition as it is generally expected that people with a better sense of humor are less likely to be depressed.
03

Assessing the applicability of simple linear regression

Simple linear regression is often used to make predictions for the dependent variable based on the independent variable. However, the strength and consistency of the relationship between the two variables influence the accuracy of these predictions. Given that the correlation coefficient is -.18 (indicating a weak negative relationship), the simple linear regression model may not provide accurate predictions in this case. However, it is important to remember that correlation does not inform of causality. Additional studies need to be conducted to determine causation.

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Key Concepts

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

Correlation Coefficient
The correlation coefficient, commonly denoted by the letter \(r\), is a statistic that measures the strength and direction of a linear relationship between two variables. It ranges from -1 to +1. An \(r\) value of +1 indicates a perfect positive correlation, while -1 indicates a perfect negative correlation. An \(r\) of 0 suggests no correlation.
In educational research, this measure helps determine how variables like coping mechanisms and mental health indicators, such as the Coping Humor Scale and Depression Scale, relate to each other. In this exercise, a correlation coefficient of \(-0.18\) was found, indicating a weak negative relationship. This suggests that an increase in one variable generally comes with a decrease in the other, albeit not strongly. Such weak correlations require careful interpretation, as they might not hold universally across different samples.
P-Value
The P-value is a crucial concept when testing hypotheses in statistics. It tells us about the probability of observing the results we have, given that there is actually no effect or relationship between the variables. In simple terms, it tests the null hypothesis.
For instance, a P-value less than 0.05, as reported in the exercise, suggests that the observed correlation (\(r = -0.18\)) is statistically significant. This means there is less than a 5% chance that this result is due to random variation. In educational studies, achieving statistical significance indicates that the findings are less likely caused by sampling error and more likely represent a true relationship.
  • A P-value < 0.05 usually means rejecting the null hypothesis (that there is no relationship).
  • It signifies that results are reliable but not necessarily strong, especially with a low \(r\).
It is a tool for understanding whether to be cautious about acting on observed data, especially when correlation is weak.
Simple Linear Regression
Simple linear regression is a method for predicting the value of a dependent variable based on the value of an independent variable. It establishes a straight-line equation that best predicts outcomes from input data.
In the context of the exercise, we would use simple linear regression to predict depression scores from the humor coping scores. The validity of such predictions heavily depends on the correlation strength between the two variables. Here, with a correlation of \(-0.18\), any predictions made using a linear regression model would likely be inaccurate.
  • Simple linear regression assumes a linear relationship.
  • With weak correlation, predictions may have high error rates.
  • Consider exploring additional variables or using more complex models for better prediction.
Although this method is straightforward, the weak relationship in this example suggests that other factors beyond just a direct relationship between the two scales need careful exploration.
Statistical Significance
Statistical significance is a determination that the relationships observed in data are unlikely to be due to chance. It helps in differentiating valid findings from those that could have happened randomly.
In educational research, determining statistical significance helps verify findings before drawing conclusions or making decisions. The P-value is commonly used to determine this significance. This exercise's P-value suggests that the negative correlation between the coping humor and depression scores is significant, despite being weak. This operationally means our results aren't just a fluke resulting from the sampling process.
  • Significance doesn't imply strong or important; it just notes likelihood beyond chance.
  • Helps in verifying whether a relationship is worth exploring further.
  • It's vital to consider other factors influencing significance to avoid false implications.
Therefore, even when the correlation is weak, statistical significance ensures that it's noted and explored appropriately, instead of being dismissed outright.

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Most popular questions from this chapter

The authors of the article used a simple linear regression model to describe the relationship between \(y=\) vigor (average width in centimeters of the last two annual rings) and \(x=\) stem density (stems/ \(\mathrm{m}^{2}\) ). The estimated model was based on the following data. Also given are the standardized residuals. \(\begin{array}{lrrrrr}x & 4 & 5 & 6 & 9 & 14 \\ y & 0.75 & 1.20 & 0.55 & 0.60 & 0.65 \\ \text { St. resid. } & -0.28 & 1.92 & -0.90 & -0.28 & 0.54 \\ x & 15 & 15 & 19 & 21 & 22 \\ y & 0.55 & 0.00 & 0.35 & 0.45 & 0.40 \\ \text { St. resid. } & 0.24 & -2.05 & -0.12 & 0.60 & 0.52\end{array}\) a. What assumptions are required for the simple linear regression model to be appropriate? b. Construct a normal probability plot of the standardized residuals. Does the assumption that the random deviation distribution is normal appear to be reasonable? Explain. c. Construct a standardized residual plot. Are there any unusually large residuals? d. Is there anything about the standardized residual plot that would cause you to question the use of the simple linear regression model to describe the relationship between \(x\) and \(y\) ?

Explain the difference between a confidence interval and a prediction interval. How can a prediction level of \(95 \%\) be interpreted?

Television is regarded by many as a prime culprit for the difficulty many students have in performing well in school. The article reported that for a random sample of \(n=528\) college students, the sample correlation coefficient between time spent watching television \((x)\) and grade point average \((y)\) was \(r=-.26\). a. Does this suggest that there is a negative correlation between these two variables in the population from which the 528 students were selected? Use a test with significance level \(.01\). b. Would the simple linear regression model explain a substantial percentage of the observed variation in grade point average? Explain your reasoning.

\(13.26\) In anthropological studies, an important characteristic of fossils is cranial capacity. Frequently skulls are at least partially decomposed, so it is necessary to use other characteristics to obtain information about capacity. One such measure that has been used is the length of the lambda- opisthion chord. The article reported the accompanying data for \(n=7\) Homo erectus fossils. \(\begin{array}{llllllll}x \text { (chord } & 78 & 75 & 78 & 81 & 84 & 86 & 87\end{array}\) length in \(\mathrm{mm}\) ) \(\begin{array}{llllllll}\text { (capacity } & 850 & 775 & 750 & 975 & 915 & 1015 & 1030\end{array}\) in \(\mathrm{cm}^{3}\) ) Suppose that from previous evidence, anthropologists had believed that for each \(1-\mathrm{mm}\) increase in chord length, cranial capacity would be expected to increase by \(20 \mathrm{~cm}^{3}\). Do these new experimental data strongly contradict prior belief?

Carbon aerosols have been identified as a contributing factor in a number of air quality problems. In a chemical analysis of diesel engine exhaust, \(x=\) mass \(\left(\mu \mathrm{g} / \mathrm{cm}^{2}\right)\) and \(y=\) elemental carbon \(\left(\mu \mathrm{g} / \mathrm{cm}^{2}\right)\) were recorded. The estimated regression line for this data set is \(\hat{y}=31+.737 x\). The accompanying table gives the observed \(x\) and \(y\) values and the corresponding standardized residuals. \(\begin{array}{lrrrrr}x & 164.2 & 156.9 & 109.8 & 111.4 & 87.0 \\\ y & 181 & 156 & 115 & 132 & 96 \\ \text { St. resid. } & 2.52 & 0.82 & 0.27 & 1.64 & 0.08 \\ x & 161.8 & 230.9 & 106.5 & 97.6 & 79.7 \\ y & 170 & 193 & 110 & 94 & 77 \\ \text { St. resid. } & 1.72 & -0.73 & 0.05 & -0.77 & -1.11 \\\ x & 118.7 & 248.8 & 102.4 & 64.2 & 89.4 \\ y & 106 & 204 & 98 & 76 & 89 \\\ \text { St. resid. } & -1.07 & -0.95 & -0.73 & -0.20 & -0.68 \\ x & 108.1 & 89.4 & 76.4 & 131.7 & 100.8 \\ y & 102 & 91 & 97 & 128 & 88 \\ \text { St. resid. } & -0.75 & -0.51 & 0.85 & 0.00 & -1.49\end{array}\) \(\begin{array}{lllll}78.9 & 387.8 & 135.0 & 82.9 & 117.9\end{array}\) a. Construct a standardized residual plot. Are there any unusually large residuals? Do you think that there are any influential observations? b. Is there any pattern in the standardized residual plot that would indicate that the simple linear regression model is not appropriate? c. Based on your plot in Part (a), do you think that it is reasonable to assume that the variance of \(y\) is the same at each \(x\) value? Explain.

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