In: Operations Management
The actual demand data for an item at a local retailer
during the past six weeks are shown below:
WEEK
ACTUAL DEMAND
(number of units)
Six weeks ago
202
Five weeks ago
201
Four weeks ago
199
Three weeks ago
200
Two weeks ago
203
One week ago
198
THIS WEEK
ACTUAL DEMAND NOT KNOWN
Determine the demand forecast for THIS WEEK using each of the following methods:
a. A 3-week moving average.
[3]
b. A 4-week weighted moving average using weights of 15, 5, 3, and 2 for one week ago, two
weeks ago, three weeks ago, and four weeks ago, respectively. (
Hint
: the higher weights
are applied to the more recent time periods.)
c. Exponential smoothing using the following: smoothing constant,
α
= 0.4 and the demand
forecast for three weeks ago = 199 units.
a) A 3-periods moving average method averages the actual value for the previous three periods to generate the forecast for the next period. This can be calculated as the sum of the actual value for the previous three periods / 3
So using the above formula the forecast for this week = (200+203+198)/3
= 601/3
= 200.33
b) using a four period weighted moving average method the formula to calculate the forecast is : Sum of the product of the actual value and their respective weights for the previous four periods/(Sum of weights).
So using this formula the forecast for this week= [(2 x 199) + (3 x 200) + (5 x 203) + (15 × 198)]/(2+3+5+15)
= (398+600+1015+2970)/25
= 4983/25
= 199.33
c) Using the exponential smoothing method the formula to calculate the forecast is as follows :
Ft = F(t-1) + [A(t-1) - F(t-1)]
Where Ft = forecast for period t
A(t-1)= actual value for period previous to t
F(t - 1)= forecast for period previous to t
= smoothing constant
So using the above formula with =0.4 and forecast for three weeks ago = 199 , the forecast for the following weeks are :