Math Problem Statement

A computer, while calculating the correlation coefficient between two variables x and y, found an error in two pairs of observations. The task is to compute the correct value of the correlation coefficient after correcting these observations.

Solution

We are given that some observations were recorded incorrectly, and the task is to find the correct correlation coefficient between xx and yy.

Given Data:

  • n=25n = 25
  • Σx=125\Sigma x = 125
  • Σy=100\Sigma y = 100
  • Σx2=650\Sigma x^2 = 650
  • Σy2=460\Sigma y^2 = 460
  • Σxy=508\Sigma xy = 508

Incorrect observations:

  • For x=6,y=14x = 6, y = 14 and x=8,y=6x = 8, y = 6

Correct observations:

  • Corrected values are x=8,y=12x = 8, y = 12 and x=6,y=8x = 6, y = 8

Step-by-step process:

  1. Adjustment to sums due to incorrect observations:

    First, calculate the incorrect contributions to the sums from the incorrect values: Incorrect sum of x=6+8=14\text{Incorrect sum of } x = 6 + 8 = 14 Incorrect sum of y=14+6=20\text{Incorrect sum of } y = 14 + 6 = 20 Incorrect x2=62+82=36+64=100\text{Incorrect } x^2 = 6^2 + 8^2 = 36 + 64 = 100 Incorrect y2=142+62=196+36=232\text{Incorrect } y^2 = 14^2 + 6^2 = 196 + 36 = 232 Incorrect xy=(6×14)+(8×6)=84+48=132\text{Incorrect } xy = (6 \times 14) + (8 \times 6) = 84 + 48 = 132

  2. Correct sums for the correct pairs of observations: Correct sum of x=8+6=14\text{Correct sum of } x = 8 + 6 = 14 Correct sum of y=12+8=20\text{Correct sum of } y = 12 + 8 = 20 Correct x2=82+62=64+36=100\text{Correct } x^2 = 8^2 + 6^2 = 64 + 36 = 100 Correct y2=122+82=144+64=208\text{Correct } y^2 = 12^2 + 8^2 = 144 + 64 = 208 Correct xy=(8×12)+(6×8)=96+48=144\text{Correct } xy = (8 \times 12) + (6 \times 8) = 96 + 48 = 144

  3. Adjust the original sums: Σxcorrected=12514+14=125\Sigma x_{\text{corrected}} = 125 - 14 + 14 = 125 Σycorrected=10020+20=100\Sigma y_{\text{corrected}} = 100 - 20 + 20 = 100 Σxcorrected2=650100+100=650\Sigma x^2_{\text{corrected}} = 650 - 100 + 100 = 650 Σycorrected2=460232+208=436\Sigma y^2_{\text{corrected}} = 460 - 232 + 208 = 436 Σxycorrected=508132+144=520\Sigma xy_{\text{corrected}} = 508 - 132 + 144 = 520

  4. Now, use the formula for the correlation coefficient rr: [ r = \frac{n \Sigma xy - (\Sigma x)(\Sigma y)}{\sqrt{[n \Sigma x^2 - (\Sigma x)^2][n \Sigma y^2 - (\Sigma y)^2]}} ] Plugging in the corrected values: [ r = \frac{25 \times 520 - (125 \times 100)}{\sqrt{[25 \times 650 - (125)^2][25 \times 436 - (100)^2]}} ] Let's compute this step by step.The correct correlation coefficient rr between xx and yy after making the necessary corrections is approximately 0.6670.667.

Would you like further clarification on any part of the process or detailed steps on how we reached this result?

Here are some related questions for further understanding:

  1. How would the correlation coefficient change if the incorrect observations were more extreme?
  2. What is the significance of the correlation coefficient being positive in this case?
  3. How can the correlation coefficient be interpreted in real-life situations involving two variables?
  4. What is the impact of having incorrect observations on the calculation of correlation coefficients?
  5. Can we determine if the relationship between xx and yy is linear or nonlinear from the correlation coefficient alone?

Tip: Always double-check observations and data before performing any statistical analysis, as incorrect entries can significantly affect the results.

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Math Problem Analysis

Mathematical Concepts

Statistics
Correlation Coefficient
Data Correction

Formulas

Sum of x (Σx), Sum of y (Σy), Sum of squares of x (Σx²), Sum of squares of y (Σy²), Sum of products of x and y (Σxy)
Correlation Coefficient: r = [nΣxy - (Σx)(Σy)] / sqrt{[nΣx² - (Σx)²][nΣy² - (Σy)²]}

Theorems

Pearson Correlation Coefficient

Suitable Grade Level

Grades 10-12