In: Statistics and Probability
Date |
Sales |
Jan-13 |
40,358 |
Feb-13 |
45,002 |
Mar-13 |
63,165 |
Apr-13 |
57,479 |
May-13 |
52,308 |
Jun-13 |
60,062 |
Jul-13 |
51,694 |
Aug-13 |
54,469 |
Sep-13 |
48,284 |
Oct-13 |
45,239 |
Nov-13 |
40,665 |
Dec-13 |
47,968 |
Jan-14 |
37,255 |
Feb-14 |
38,521 |
Mar-14 |
55,110 |
Apr-14 |
51,389 |
May-14 |
58,068 |
Jun-14 |
64,028 |
Jul-14 |
52,873 |
Aug-14 |
62,584 |
Sep-14 |
53,373 |
Oct-14 |
52,060 |
Nov-14 |
51,727 |
Dec-14 |
51,455 |
Jan-15 |
47,906 |
Feb-15 |
53,570 |
Mar-15 |
69,189 |
Apr-15 |
64,346 |
May-15 |
77,267 |
Jun-15 |
75,787 |
Jul-15 |
74,052 |
Aug-15 |
79,756 |
Sep-15 |
73,292 |
Oct-15 |
77,207 |
Nov-15 |
68,423 |
Dec-15 |
67,274 |
Jan-16 |
65,711 |
Feb-16 |
68,005 |
Mar-16 |
78,029 |
Apr-16 |
92,764 |
May-16 |
97,175 |
Jun-16 |
86,255 |
Jul-16 |
90,496 |
Aug-16 |
87,602 |
Sep-16 |
83,577 |
Oct-16 |
92,610 |
Nov-16 |
73,949 |
Dec-16 |
77,711 |
Page 277
(c5p12)
It seems that the sales are the lowest in November, December, January, and February than in other months. Therefore, I agree with this statement.
The trend model given with this equation is 45518.48+927.7418*t-15281.1*x2-12738.8*x2-13645*x11-12158.7*x12. They support Ronnie’s observations because
Jan-2017 |
87327 |
Feb-2017 |
84772 |
Mar-2017 |
112499 |
Apr-2017 |
102633 |
May-2017 |
112996 |
Jun-2017 |
119807 |
Solution:
The time-series plot is:
Yes, sales data for the four-year period indicates that sales are slowest in November, December, January, and February than in other months.
The output is:
Regression Statistics | ||||||||
Multiple R | 0.93343 | |||||||
R Square | 0.871291 | |||||||
Adjusted R Square | 0.822079 | |||||||
Standard Error | 6688.479 | |||||||
Observations | 48 | |||||||
ANOVA | ||||||||
df | SS | MS | F | Significance F | ||||
Regression | 13 | 1.03E+10 | 7.92E+08 | 17.70482 | 1.88E-11 | |||
Residual | 34 | 1.52E+09 | 44735747 | |||||
Total | 47 | 1.18E+10 | ||||||
Coefficients | Standard Error | t Stat | P-value | Lower 95% | Upper 95% | Lower 95.0% | Upper 95.0% | |
Intercept | 45518.48 | 2108.71 | 21.58594 | 2E-21 | 41233.07 | 49803.9 | 41233.07 | 49803.9 |
t | 924.7418 | 71.26704 | 12.97573 | 1E-14 | 779.9097 | 1069.574 | 779.9097 | 1069.574 |
x1 | -15281.1 | 3568.693 | -4.28198 | 0.000143 | -22533.5 | -8028.62 | -22533.5 | -8028.62 |
x2 | -12738.8 | 3561.57 | -3.57674 | 0.001069 | -19976.8 | -5500.84 | -19976.8 | -5500.84 |
x3 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x4 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x5 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x6 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x7 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x8 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x9 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x10 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x11 | -13645 | 3561.57 | -3.83117 | #NUM! | -20883 | -6407.01 | -20883 | -6407.01 |
x12 | -12158.7 | 3568.693 | -3.40706 | 0.001703 | -19411.2 | -4906.28 | -19411.2 | -4906.28 |
The trend model that includes a time index and dummy variables is:
Sales = 45518.48 + 924.7418*t - 15281.1*x2 - 12738.8*x2 - 13645*x11 - 12158.7*x12
These results support Ronnie’s observations because the four-year period indicates that sales are slowest in November, December, January, and February than in other months.
The output is:
Regression Statistics | ||||||||
Multiple R | 0.952126 | |||||||
R Square | 0.906544 | |||||||
Adjusted R Square | 0.866896 | |||||||
Standard Error | 5785.089 | |||||||
Observations | 48 | |||||||
ANOVA | ||||||||
df | SS | MS | F | Significance F | ||||
Regression | 14 | 1.07E+10 | 7.65E+08 | 22.86478 | 5.18E-13 | |||
Residual | 33 | 1.1E+09 | 33467250 | |||||
Total | 47 | 1.18E+10 | ||||||
Coefficients | Standard Error | t Stat | P-value | Lower 95% | Upper 95% | Lower 95.0% | Upper 95.0% | |
Intercept | 53731.77 | 2724.102 | 19.72459 | 7.81E-20 | 48189.55 | 59274 | 48189.55 | 59274 |
t | -45.0203 | 246.7313 | -0.18247 | 0.856333 | -546.999 | 456.9583 | -546.999 | 456.9583 |
t² | 19.79106 | 4.875659 | 4.059156 | 0.000284 | 9.87146 | 29.71067 | 9.87146 | 29.71067 |
x1 | -15775.9 | 3089.087 | -5.10696 | 1.35E-05 | -22060.6 | -9491.06 | -22060.6 | -9491.06 |
x2 | -13035.7 | 3081.389 | -4.23046 | 0.000174 | -19304.8 | -6766.55 | -19304.8 | -6766.55 |
x3 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x4 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x5 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x6 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x7 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x8 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x9 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x10 | 0 | 0 | 65535 | #NUM! | 0 | 0 | 0 | 0 |
x11 | -13941.9 | 3081.389 | -4.52454 | #NUM! | -20211 | -7672.73 | -20211 | -7672.73 |
x12 | -12653.5 | 3089.087 | -4.0962 | 0.000256 | -18938.3 | -6368.72 | -18938.3 | -6368.72 |
There is no evidence of the increase in sales growth.
Actual | Forecasted | Error | |
87327 | 83268.27 | 4058.732 | 5% |
84772 | 87922.73 | 3150.732 | 4% |
112499 | 102912.3 | 9586.707 | 9% |
102633 | 104905.8 | 2272.752 | 2% |
112996 | 106938.8 | 6057.206 | 5% |
119807 | 109011.4 | 10795.58 | 9% |
MAPE | 6% |