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Midterm-final correlation For students who take Statistics 101 at Lake Wobegon College in Minnesota, both the midterm and final exams have mean \(=75\) and standard deviation \(=10 .\) The professor explores using the midterm exam score to predict the final exam score. The regression equation relating \(y=\) final exam score to \(x=\) midterm exam score is \(\hat{y}=30+0.60 x\). a. Find the predicted final exam score for a student who has (i) midterm score \(=100,\) (ii) midterm score \(=50\). Note that in each case the predicted final exam score regresses toward the mean of \(75 .\) (This is a property of the regression equation that is the origin of its name, as Chapter 12 will explain.) b. Show that the correlation equals 0.60 and interpret it. (Hint: Use the relation between the slope and correlation.)

Short Answer

Expert verified
Predicted scores are 90 (midterm 100) and 60 (midterm 50). Correlation is 0.60, showing a moderate positive relationship.

Step by step solution

01

Calculate Predicted Final Exam Score for Midterm Score 100

Use the regression equation \( \hat{y} = 30 + 0.60x \) where \( x = 100 \). Substitute \( x = 100 \) into the equation:\[\hat{y} = 30 + 0.60 \times 100 = 30 + 60 = 90\]The predicted final exam score for a midterm score of 100 is 90.
02

Calculate Predicted Final Exam Score for Midterm Score 50

Use the same regression equation \( \hat{y} = 30 + 0.60x \) and substitute \( x = 50 \) into it:\[\hat{y} = 30 + 0.60 \times 50 = 30 + 30 = 60\]The predicted final exam score for a midterm score of 50 is 60.
03

Verify the Correlation Using the Slope

The regression slope \( b = 0.60 \) is related to the correlation coefficient \( r \) through the formula: \[ b = r \left(\frac{s_y}{s_x}\right) \]Given \( s_y = 10 \) and \( s_x = 10 \), substitute these into the formula:\[ 0.60 = r \left(\frac{10}{10}\right) \Rightarrow 0.60 = r\]Thus, the correlation coefficient is 0.60. This indicates a moderate positive linear relationship between the midterm and final exam scores.

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Key Concepts

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

Understanding Regression Analysis
Regression analysis is a critical concept in educational statistics that helps us understand relationships between two variables. It's like a mathematical tool that allows us to predict the outcome of one variable based on the value of another. Here, in our exercise, we use regression analysis to predict final exam scores using midterm scores.

The equation given is a simple linear regression: \[\hat{y} = 30 + 0.60x\]where \( \hat{y} \) is the predicted final score, and \( x \) is the midterm score. The number 30 is the intercept; it tells us where the line crosses the y-axis when the midterm score is zero. The 0.60 is the slope of the line, indicating how much the final score is expected to increase for each additional point scored on the midterm.

In simpler terms, if a student scores higher on the midterm, the regression analysis suggests they will likely score better on the final. The intercept and slope provide specific guidance on how scores are transformed from one phase to another.
Exploring the Correlation Coefficient
The correlation coefficient is a crucial part of regression analysis and statistics in general. This statistic tells us about the strength and direction of the linear relationship between two variables. In the context of our exercise, the correlation coefficient is 0.60.

- **Value Range:** Correlation coefficients range from -1 to 1. - **Positive Correlation:** A positive number means that as one variable increases, the other also increases. Here, both exam scores tend to rise together. - **Strength Indicator:** Our value of 0.60 suggests a moderate positive relationship. It isn't perfect but indicates a trend where higher midterm performance is associated with higher final exam scores.

This moderate correlation means that while midterm scores are a good predictor of final scores, they aren't the only factor. Other variables could affect a student's performance, such as study habits or test material difficulty.
Introduction to Predictive Modeling
Predictive modeling in statistics utilizes various algorithms to predict future outcomes based on historical data. In educational settings, it helps forecast student performances, like in our exercise with exam scores.

Our regression equation is a basic example of predictive modeling where past performances (midterm scores) aim to predict future outcomes (final scores). By analyzing patterns and relationships within the data, predictive modeling provides insights that can guide educational strategies and improve student outcomes.

Predictive models can grow in complexity. Here, we used a linear model with a single predictor (the midterm scores). More advanced models might include multiple variables, such as homework scores or attendance, and use different types of regression to get more accurate predictions and insights.

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