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Math Help - Help with Regression

  1. #1
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    Help with Regression

    I'm doing a regression project inn Excel for my statistics class. One of the questions I'm supposed to solve for doesn't make any sense to me. I was hoping that someone could help clarify what exactly I'm supposed to do in this situation.

    "Run a regression of the variable on a polynomial function on time and analyze the relationship. Fit the best model and decide on the degree of the polynomial."

    I know how to run a regression of my variable on time but I don't understand where the polynomial function is supposed to come from or how I'm supposed to implement it into the regression. I don't think the polynomial function is my estimate y function from computing the regression of just my variable on time because I tried adding that to my regression in Excel and its t value was 0 so it's useless.
    Last edited by haen; December 6th 2007 at 12:03 PM.
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  2. #2
    MHF Contributor
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    You'll have to do better than that. Exactly what are you doing?

    What sort of data have you?
    Are your data evenly spaced? (Every month or week?)
    Do you know how to chart the regression function?
    What is your experience level with Excel?
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  3. #3
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    Quote Originally Posted by TKHunny View Post
    What sort of data have you? Are your data evenly spaced? (Every month or week?)
    closing friday stock value of Google for 148 weeks.

    Quote Originally Posted by TKHunny View Post
    Do you know how to chart the regression function?
    What is your experience level with Excel?
    I'm not entirely sure what you mean by chart the regression function but I'm able to get a linear function that runs through my data. I would say that my experience level with Excel is novice given the capabilities of the program.
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  4. #4
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    Good start. How did yo get that linear function? Did you use the "Add Trendline" feature? If you created the trendline yourself, and just put it on the same chart, it's a little trickier.

    If it were me, I'd do this:

    1) Enter the 148 weeks of data in one column.
    2) Select all the data.
    3) Draw a super quick chart [alt]-I-H-F (Or from the menu Insert-cHart-Finish)

    My default chart is set to "Line". If your's isn't, you will want to pick "line" before hitting the "Finish" button.

    4) Once you get the chart with the lovely jagged line, Right Click the line and pick "Add Trendline"

    5) There should be a "Type" tab. Pick "Polynomial" and leave the degree set to 2.

    6) Click the Options Tab
    7) Click "Display Equation on Chart" and "Display R-Squared Value on Chart"
    8) Click "OK"

    Now you get to play with it.

    9) Look at the R-Squared value. Write it down.
    10) Right click the trend quadratic, Pick "Format TrendLine"
    11) Click the "Type" tab and change the degree to 3.
    12) Click "OK"

    Repeat steps 9-12 until you find what you seek. It goes only to degree 6, so don't worry about being there all day.

    Show us what you get.
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