Section 4.2 How Can We Define the Relationship between two

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Section 4.2 How Can We Define the Relationship between two sets of Quantitative Data?

Consider the Relationship Between Length and Weight in some Lengths of Channel Iron:

Scatter Plot

Find an Equation by Hand: Pick two points that define a line of best fit (the points do not have to be part of the data) … how about (19,160) & (56,518) y = mx + b ( slope = m = 𝑦 2 − 𝑦 1 𝑥 2 − 𝑥 1 ) … so m = 518−160 56−19 ≈9.68 Find b by plugging in the slope and one of the two points … 160 = 9.68(19) + b … so b = -23.92 So y = 9.68x – 23.92 models the relation ship between length (x) and weight (y) What do m & b represent in the data beyond slope and y-intercept?

Use the Equation: How much will a 72 length of channel weigh? y = 9.68(72) – 23.92 ≈ 673 lbs. How long would a length of channel be weighing 250 lbs.? 250 = 9.68x – 23.92, x ≈ 28.3 ft.

Least Squares Regression: A least squares regression line minimizes the sum of the squared vertical distance between the observed and predicted value. We name it 𝑦 , pronounced (y – hat) 𝑦 = mx + b … where m = r ∙ 𝑠 𝑦 𝑠 𝑥 & b = 𝑦 −𝑚 𝑥 𝑥 = 35.8 & Sx = 15.1888 𝑦 = 319.6 & Sy = 151.4754 r = .998 𝑦 = mx + b … where m = 9.953 & b = -36.72

Three Cheers for Technology: Stat … Calc … LinReg ( ax + b ) Shazaam! … 𝑦 = 9.956x – 36.833 Why is there a difference in the values from doing it by hand? What is the correlation coefficient (r – value)? r ≈ .998 Web link to a good graphing calculator regression tutorial youtube: http://www.youtube.com/watch?v=nw6GOUtC2jY

Temp/Elevation Correlation: Temperature 1542 ft 74 F 2238 ft 73 F 5426 ft 70 F 8634 ft 58 F Find 𝑦 and its correlation coefficient Graph the data and the line of best fit ( 𝑦 ) on your calculator Estimate the temperature on the top of Mt. Shasta … elevation 14,179 ft. Estimate the elevation if the temperature is 40 degrees.