Question
The following data report total, monthly U.S. gasoline sales in millions of dollars from January 2017 to December 2018. (To find the data, go to
The following data report total, monthly U.S. gasoline sales in millions of dollars from January 2017 to December 2018. (To find the data, go to the site https://www.census.gov/retail/index.html#mrts, find "Monthly Retail Trade Report," then select "Time Series/Trend Charts.")
d. Evaluate a seasonally adjusted trend forecasting model. What is the MAD? (Round your answers to 3 decimal places.)
Period | Month-Year | Month | Sales ($ Million) | Trend | Index | Forecast | Absolute Error |
1 | Jan-2017 | 1 | 35,030 | 36,409.800 | 0.960 | ||
2 | Feb-2017 | 2 | 33,372 | 36,828.600 | 0.906 | ||
3 | Mar-2017 | 3 | 38,022 | 37,247.400 | 1.020 | ||
4 | Apr-2017 | 4 | 38,373 | 37,666.200 | 1.019 | ||
5 | May-2017 | 5 | 40,139 | 38,085.000 | 1.054 | ||
6 | Jun-2017 | 6 | 39,409 | 38,503.800 | 1.024 | ||
7 | Jul-2017 | 7 | 39,197 | 38,922.600 | 1.007 | ||
8 | Aug-2017 | 8 | 40,617 | 39,341.400 | 1.032 | ||
9 | Sep-2017 | 9 | 40,746 | 39,760.200 | 1.025 | ||
10 | Oct-2017 | 10 | 41,117 | 40,179.000 | 1.023 | ||
11 | Nov-2017 | 11 | 39,586 | 40,597.800 | 0.975 | ||
12 | Dec-2017 | 12 | 39,446 | 41,016.600 | 0.962 | ||
13 | Jan-2018 | 1 | 38,623 | 41,435.400 | 0.932 | ||
14 | Feb-2018 | 2 | 36,777 | 41,854.200 | 0.879 | ||
15 | Mar-2018 | 3 | 42,048 | 42,273.000 | 0.995 | ||
16 | Apr-2018 | 4 | 42,509 | 42,691.800 | 0.996 | ||
17 | May-2018 | 5 | 47,449 | 43,110.600 | 1.101 | ||
18 | Jun-2018 | 6 | 46,946 | 43,529.400 | 1.078 | ||
19 | Jul-2018 | 7 | 47,391 | 43,948.200 | 1.078 | ||
20 | Aug-2018 | 8 | 48,233 | 44,367.000 | 1.087 | ||
21 | Sep-2018 | 9 | 44,985 | 44,785.800 | 1.004 | ||
22 | Oct-2018 | 10 | 47,742 | 45,204.600 | 1.056 | ||
23 | Nov-2018 | 11 | 42,639 | 45,623.400 | 0.935 | ||
24 | Dec-2018 | 12 | 39,026 | 46,042.200 | 0.848 | ||
MAD= |
I am struggling to find the correct formula/process to find the seasonally adjusted forecast and Absolute Error, I did fine with the trend and index on the chart above.
The next question is
e. What are the monthly indexes for months 1-12, I put the numbers I got in the chart above but it shows up as incorrect.
The last question is
f. Forecast sales for January, February, March, and April of 2019.
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