Math Problem Statement

The table below gives the list price and the number of bids received for five randomly selected items sold through online auctions. Using this data, consider the equation of the regression line, yˆ=b0+b1x , for predicting the number of bids an item will receive based on the list price. Keep in mind, the correlation coefficient may or may not be statistically significant for the data given. Remember, in practice, it would not be appropriate to use the regression line to make a prediction if the correlation coefficient is not statistically significant.

Price in Dollars 23 34 44 46 50 Number of Bids 1 2 4 9 10 Table

Step 6 of 6 : Find the value of the coefficient of determination. Round your answer to three decimal places.

Solution

To find the coefficient of determination (R2R^2), we first need to calculate the correlation coefficient (rr), and then square it to obtain R2R^2. The coefficient of determination indicates how well the regression line explains the variability in the number of bids based on the list price.

Given Data:

  • Prices (xx): 23, 34, 44, 46, 50
  • Number of bids (yy): 1, 2, 4, 9, 10

Steps to Calculate the Coefficient of Determination:

  1. Calculate the Mean of xx and yy: xˉ=23+34+44+46+505=1975=39.4\bar{x} = \frac{23 + 34 + 44 + 46 + 50}{5} = \frac{197}{5} = 39.4 yˉ=1+2+4+9+105=265=5.2\bar{y} = \frac{1 + 2 + 4 + 9 + 10}{5} = \frac{26}{5} = 5.2

  2. Calculate the Covariance of xx and yy: Cov(x,y)=(xixˉ)(yiyˉ)n\text{Cov}(x, y) = \frac{\sum (x_i - \bar{x})(y_i - \bar{y})}{n} Where n=5n = 5 is the number of data points.

  3. Calculate the Standard Deviations of xx and yy: σx=(xixˉ)2n\sigma_x = \sqrt{\frac{\sum (x_i - \bar{x})^2}{n}} σy=(yiyˉ)2n\sigma_y = \sqrt{\frac{\sum (y_i - \bar{y})^2}{n}}

  4. Find the Correlation Coefficient rr: r=Cov(x,y)σxσyr = \frac{\text{Cov}(x, y)}{\sigma_x \sigma_y}

  5. Calculate the Coefficient of Determination R2R^2: R2=r2R^2 = r^2

Let me now calculate each of these steps to find the R2R^2 value. numpy as np

Given data

x = np.array([23, 34, 44, 46, 50]) y = np.array([1, 2, 4, 9, 10])

Step 1: Calculate the means of x and y

x_bar = np.mean(x) y_bar = np.mean(y)

Step 2: Calculate Covariance

cov_xy = np.mean((x - x_bar) * (y - y_bar))

Step 3: Calculate Standard Deviations of x and y

sigma_x = np.std(x, ddof=0) sigma_y = np.std(y, ddof=0)

Step 4: Calculate the correlation coefficient

r = cov_xy / (sigma_x * sigma_y)

Step 5: Calculate the coefficient of determination

R_squared = r**2

R_squaredThe value of the coefficient of determination (R2R^2) is approximately 0.773.

This means that about 77.3% of the variability in the number of bids can be explained by the list price according to the regression model.

Would you like any further details on the calculation or the interpretation of the result?

Here are 5 related questions you might find helpful:

  1. What does a high value of R2R^2 imply in terms of prediction accuracy?
  2. How do we interpret the correlation coefficient rr in this context?
  3. What are the conditions for using linear regression in predicting outcomes like this?
  4. How do you calculate the regression line equation for this data?
  5. How can we test the statistical significance of the correlation coefficient?

Tip: When interpreting R2R^2, remember that a higher value indicates that the regression model explains a greater proportion of the variance in the dependent variable.

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Math Problem Analysis

Mathematical Concepts

Linear Regression
Statistics
Correlation
Coefficient of Determination

Formulas

yˆ = b0 + b1x
R^2 = r^2
r = Cov(x, y) / (σx * σy)
Cov(x, y) = Σ(xi - x̄)(yi - ȳ) / n
σx = √(Σ(xi - x̄)^2 / n)
σy = √(Σ(yi - ȳ)^2 / n)

Theorems

Coefficient of Determination
Correlation Coefficient

Suitable Grade Level

Grades 11-12