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#1
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Predicting new Ys given new Xs using known relationship for X and
Hello. I know people have posted similar questions about using an existing
relationship between X and Y to predict new Ys given new Xs but I think mine has a slightly different twist. I would appreciate any help that could be offered. I have 20 data points for both X and Y. Each X point represents the number of workers on a farm for a particular year over a 20-year period. Each Y point represents the amount of crop harvest each year over that same period. The data is from 1901 to 1920. When I plot the points and fit an exponential trend line I get a high R-square of .9 . I would like to assume that the number of workers for that same 20-year period was actually 20% lower than the actual number of workers. Using this new population of workers I would like to predict the new amount of crop that could be harvested. When I do this using the function: Growth(known_y's,known_x's,new_x's,const) I get results that do not seem to be intuitively correct. For example, the new population in 1916 is approximately equal to the actual population in 1908 but the amount of crop that is expected to be harvested differs widely. Thanks in advance for any help. I would be happy to send the actual numbers I'm working with if that would be helpful in clarifying my question. |
#2
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malwatson -
From your description I don't see anything obviously wrong. Please post the X and Y historical data. Also, post the values of the arguments of GROWTH you're using and the results you're getting. - Mike www.mikemiddleton.com ++++++++++++++++++++++++++++ "malwatson" wrote in message ... Hello. I know people have posted similar questions about using an existing relationship between X and Y to predict new Ys given new Xs but I think mine has a slightly different twist. I would appreciate any help that could be offered. I have 20 data points for both X and Y. Each X point represents the number of workers on a farm for a particular year over a 20-year period. Each Y point represents the amount of crop harvest each year over that same period. The data is from 1901 to 1920. When I plot the points and fit an exponential trend line I get a high R-square of .9 . I would like to assume that the number of workers for that same 20-year period was actually 20% lower than the actual number of workers. Using this new population of workers I would like to predict the new amount of crop that could be harvested. When I do this using the function: Growth(known_y's,known_x's,new_x's,const) I get results that do not seem to be intuitively correct. For example, the new population in 1916 is approximately equal to the actual population in 1908 but the amount of crop that is expected to be harvested differs widely. Thanks in advance for any help. I would be happy to send the actual numbers I'm working with if that would be helpful in clarifying my question. |
#3
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Dear Mike,
Thanks for your quick response. Here is the data I'm analyzing: Year Actual pop. Act. Produc. New Pop. New Production 1907 58,073 1,810,000 51,115 2,038,541 1908 57,070 2,804,000 48,869 1,922,837 1909 77,524 5,396,000 65,866 2,992,151 1910 128,446 10,878,000 113,123 10,231,406 1911 166,015 17,584,000 146,535 24,403,674 1912 188,050 31,276,000 166,935 41,490,691 1913 188,250 47,440,000 165,613 40,087,515 1914 161,379 62,024,000 136,951 19,017,921 1915 170,741 113,564,000 144,563 23,182,750 1916 196,123 125,626,000 168,172 42,847,677 1917 220,758 160,044,000 191,015 77,628,495 1918 201,964 156,778,000 170,719 45,783,112 1919 237,134 212,906,000 205,197 112,269,217 1920 216,588 202,660,000 184,062 64,782,937 I'm trying to use the new population numbers in the 4th column to project the new production amount in the last column. I used the following excel command to generate the numbers in the last column: =GROWTH(C44:C57,B44:B57,D44:D57,TRUE) Based on juse eyeballing the new numbers they do not seem to be correct. The 'actual production' numbers increase every year excep for 2 years but the 'new production' numbers seem to fluctuate widely. The production numbers represent pounds of product. If I compare the pound of product produced per person for the actual and new they are also widely divergent. I'm not sure if it would be more correct to just take the pounds produced per person for the actual numbers and multiply it by the new population to get the new production. There are other things happening over this 20-year period besides simply the labor force though that affect production and that is why I thought using the 'Growth' command made sense. Other factors affecting production would include price changes in the product and the lag between planting the crop and when it is ready to harvest. I thought using the 'Growth' command would be a more objective way of generating a trend most similar to the actual one. Thanks again. "Michael R Middleton" wrote: malwatson - From your description I don't see anything obviously wrong. Please post the X and Y historical data. Also, post the values of the arguments of GROWTH you're using and the results you're getting. - Mike www.mikemiddleton.com ++++++++++++++++++++++++++++ "malwatson" wrote in message ... Hello. I know people have posted similar questions about using an existing relationship between X and Y to predict new Ys given new Xs but I think mine has a slightly different twist. I would appreciate any help that could be offered. I have 20 data points for both X and Y. Each X point represents the number of workers on a farm for a particular year over a 20-year period. Each Y point represents the amount of crop harvest each year over that same period. The data is from 1901 to 1920. When I plot the points and fit an exponential trend line I get a high R-square of .9 . I would like to assume that the number of workers for that same 20-year period was actually 20% lower than the actual number of workers. Using this new population of workers I would like to predict the new amount of crop that could be harvested. When I do this using the function: Growth(known_y's,known_x's,new_x's,const) I get results that do not seem to be intuitively correct. For example, the new population in 1916 is approximately equal to the actual population in 1908 but the amount of crop that is expected to be harvested differs widely. Thanks in advance for any help. I would be happy to send the actual numbers I'm working with if that would be helpful in clarifying my question. |
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