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Production Planning and Control
Production Planning and Control
1. Naive approach2. Moving averages3. Exponential
smoothing4. Trend projection
5. Linear regression
Time-Series Time-Series ModelsModels
Associative Associative ModelModel
Set of evenly spaced numerical data Obtained by observing response variable
at regular time periods Forecast based only on past values, no
other variables important Assumes that factors influencing past
and present will continue influence in future
Trend
Seasonal
Cyclical
Random
Dem
and
fo
r p
rod
uct
or
serv
ice
| | | |1 2 3 4
Year
Average demand over four years
Seasonal peaks
Trend component
Actual demand
Random variation
Persistent, overall upward or downward pattern
Changes due to population, technology, age, culture, etc.
Typically several years duration
Regular pattern of up and down fluctuations
Due to weather, customs, etc. Occurs within a single year
Number ofPeriod Length Seasons
Week Day 7Month Week 4-4.5Month Day 28-31Year Quarter 4Year Month 12Year Week 52
Repeating up and down movements Affected by business cycle, political,
and economic factors Multiple years duration Often causal or
associative relationships
00 55 1010 1515 2020
Erratic, unsystematic, ‘residual’ fluctuations
Due to random variation or unforeseen events
Short duration and nonrepeating
MM TT WW TT FF
Assumes demand in next Assumes demand in next period is the same as period is the same as demand in most recent perioddemand in most recent period e.g., If January sales were 68, then e.g., If January sales were 68, then
February sales will be 68February sales will be 68
Sometimes cost effective and Sometimes cost effective and efficientefficient
Can be good starting pointCan be good starting point
Recent periods are the best predictors of the future
Adjustments to naive modelstt YY 1
ˆ
)(ˆ11 tttt YYYY
11
ˆ
t
ttt Y
YYY
Trend
Rate of Change
Period t Year Quarter Sales1 1990 1 5002 2 3503 3 2504 4 4005 1991 1 4506 2 3507 3 2008 4 3009 1992 1 35010 2 20011 3 15012 4 40013 1993 1 55014 2 35015 3 25016 4 55017 1994 1 55018 2 40019 3 35020 4 60021 1995 1 75022 2 50023 3 40024 4 65025 1996 1 85026 2 60027 3 45028 4 700
tt YY 1ˆ
65025 Y
Use 1990-95 as initializationUse 1996 as the test data set
Forecast the first period in 1996
Forecast error:
252525 YYe
65085025 e
Forecast for the remaining 1996 quarters and calculate the error - what do you see happening?
Nonstationary - data values increase over time
)(ˆ11 tttt YYYY
900ˆ
)400650(650ˆ
)(ˆ
25
25
23242425
Y
Y
YYYY252525 YYe
90085025 e
11
ˆ
t
ttt Y
YYY
400
650 650ˆ
ˆ
25
23
242425
Y
Y
YYY 252525 YYe
105685025 e
Can also use Naïve models for seasonal forecasts - data indicates that Quarter 1 seems to be higher than 2,3,4.
MA is a series of arithmetic means Used if little or no trend Used often for smoothing
Provides overall impression of data over time
Moving average =Moving average = ∑∑ demand in previous n periodsdemand in previous n periodsnn
This method is appropriate when there is no noticeable trend or seasonality.
JanuaryJanuary 1010FebruaryFebruary 1212MarchMarch 1313AprilApril 1616MayMay 1919JuneJune 2323JulyJuly 2626
ActualActual 3-Month3-MonthMonthMonth Shed SalesShed Sales Moving AverageMoving Average
(12 + 13 + 16)/3 = 13 (12 + 13 + 16)/3 = 13 22//33
(13 + 16 + 19)/3 = 16(13 + 16 + 19)/3 = 16(16 + 19 + 23)/3 = 19 (16 + 19 + 23)/3 = 19 11//33
101012121313
((1010 + + 1212 + + 1313)/3 = 11 )/3 = 11 22//33
Period t Year Quarter Sales1 1990 1 5002 2 3503 3 2504 4 4005 1991 1 4506 2 3507 3 2008 4 3009 1992 1 35010 2 20011 3 15012 4 40013 1993 1 55014 2 35015 3 25016 4 55017 1994 1 55018 2 40019 3 35020 4 60021 1995 1 75022 2 50023 3 40024 4 65025 1996 1 85026 2 60027 3 45028 4 700
If you suspect seasonality, with quarterly data, it makes sense to use a 4-period moving average (monthly data would use a 12 period moving average). The larger the number of periods, the smoother the fluctuations become.
575ˆ4
750500400650ˆ
4ˆ
25
25
2122232425
Y
Y
yyyyY
650ˆ4
850600450700ˆ
4ˆ
29
29
2526272829
Y
Y
yyyyY
275
575850
ˆ
25
25
252525
e
e
yye
| | | | | | | | | | | |
JJ FF MM AA MM JJ JJ AA SS OO NN DD
Sh
ed S
ales
Sh
ed S
ales
30 30 –28 28 –26 26 –24 24 –22 22 –20 20 –18 18 –16 16 –14 14 –12 12 –10 10 –
Actual Actual SalesSales
Moving Moving Average Average ForecastForecast
Used when trend is present Older data usually less important
Weights based on experience and intuition
WeightedWeightedmoving averagemoving average ==
∑∑ (weight for period n)(weight for period n) x (demand in period n) x (demand in period n)
∑∑ weightsweights
JanuaryJanuary 1010FebruaryFebruary 1212MarchMarch 1313AprilApril 1616MayMay 1919JuneJune 2323JulyJuly 2626
ActualActual 3-Month Weighted3-Month WeightedMonthMonth Shed SalesShed Sales Moving AverageMoving Average
[(3 x 16) + (2 x 13) + (12)]/6 = 14[(3 x 16) + (2 x 13) + (12)]/6 = 1411//33
[(3 x 19) + (2 x 16) + (13)]/6 = 17[(3 x 19) + (2 x 16) + (13)]/6 = 17[(3 x 23) + (2 x 19) + (16)]/6 = 20[(3 x 23) + (2 x 19) + (16)]/6 = 2011//22
101012121313
[(3 x [(3 x 1313) + (2 x ) + (2 x 1212) + () + (1010)]/6 = 12)]/6 = 1211//66
Weights Applied Period
3 Last month2 Two months ago1 Three months ago6 Sum of weights
Increasing n smooths the forecast but makes it less sensitive to changes
Do not forecast trends well Require extensive historical data
To determine how many periods to use for a moving average, remember: The smaller the number, the more weight
given to recent periods. A smaller number is desirable when there
are sudden shifts in the level of the series. The greater the number, less weight is
given to more recent periods. A larger number is desirable when there
are wide or infrequent fluctuations in the data
30 30 –
25 25 –
20 20 –
15 15 –
10 10 –
5 5 –
Sa
les
de
man
dS
ale
s d
em
and
| | | | | | | | | | | |
JJ FF MM AA MM JJ JJ AA SS OO NN DD
Actual Actual salessales
Moving Moving averageaverage
Weighted Weighted moving moving averageaverage
Figure 4.2Figure 4.2
Form of weighted moving average Weights decline exponentially Most recent data weighted most
Requires smoothing constant () Ranges from 0 to 1 Subjectively chosen
Involves little record keeping of past data
New forecast =New forecast = Last period’s forecastLast period’s forecast+ + (Last period’s actual demand (Last period’s actual demand
– – Last period’s forecast)Last period’s forecast)
FFtt = F = Ft – 1t – 1 + + (A(At – 1t – 1 - F - Ft – 1t – 1))
wherewhere FFtt == new forecastnew forecast
FFt – 1t – 1 == previous forecastprevious forecast
== smoothing (or weighting) smoothing (or weighting) constant (0 constant (0 ≤≤ ≤≤ 1) 1)
Predicted demand = 142 Ford MustangsPredicted demand = 142 Ford MustangsActual demand = 153Actual demand = 153Smoothing constant Smoothing constant = .20 = .20
FFtt = F = Ft – 1t – 1 + + (A(At – 1t – 1 - F - Ft – 1t – 1))wherewhere FFtt == new forecastnew forecast
FFt – 1t – 1 == previous forecastprevious forecast
== smoothing (or weighting) smoothing (or weighting) constant (0 constant (0 ≤≤ ≤≤ 1) 1)
Weight Assigned toWeight Assigned to
MostMost 2nd Most2nd Most 3rd Most3rd Most 4th Most4th Most 5th Most5th MostRecentRecent RecentRecent RecentRecent RecentRecent RecentRecent
SmoothingSmoothing PeriodPeriod PeriodPeriod PeriodPeriod PeriodPeriod PeriodPeriodConstantConstant (()) (1 - (1 - )) (1 - (1 - ))22 (1 - (1 - ))33 (1 - (1 - ))44
= .1= .1 .1.1 .09.09 .081.081 .073.073 .066.066
= .5= .5 .5.5 .25.25 .125.125 .063.063 .031.031
Predicted demand = 142 Ford MustangsPredicted demand = 142 Ford MustangsActual demand = 153Actual demand = 153Smoothing constant Smoothing constant = .20 = .20
New forecastNew forecast = 142 + .2(153 – 142)= 142 + .2(153 – 142)
Predicted demand = 142 Ford MustangsPredicted demand = 142 Ford MustangsActual demand = 153Actual demand = 153Smoothing constant Smoothing constant = .20 = .20
New forecastNew forecast = 142 + .2(153 – 142)= 142 + .2(153 – 142)
= 142 + 2.2= 142 + 2.2
= 144.2 ≈ 144 cars= 144.2 ≈ 144 cars
225 225 –
200 200 –
175 175 –
150 150 –| | | | | | | | |
11 22 33 44 55 66 77 88 99
QuarterQuarter
De
ma
nd
De
ma
nd
= .1= .1
Actual Actual demanddemand
= .5= .5
225 225 –
200 200 –
175 175 –
150 150 –| | | | | | | | |
11 22 33 44 55 66 77 88 99
QuarterQuarter
De
ma
nd
De
ma
nd
= .1= .1
Actual Actual demanddemand
= .5= .5Chose high values of Chose high values of when underlying average when underlying average is likely to changeis likely to change
Choose low values of Choose low values of when underlying average when underlying average is stableis stable
The objective is to obtain the most The objective is to obtain the most accurate forecast no matter the accurate forecast no matter the techniquetechnique
We generally do this by selecting the We generally do this by selecting the model that gives us the lowest forecast model that gives us the lowest forecast errorerror
Forecast errorForecast error = Actual demand - Forecast value= Actual demand - Forecast value
= A= Att - F - Ftt
Mean Absolute Deviation (MAD)Mean Absolute Deviation (MAD)
MAD =MAD =∑∑ |Actual - Forecast||Actual - Forecast|
nn
Mean Squared Error (MSE)Mean Squared Error (MSE)
MSE =MSE =∑∑ (Forecast Errors)(Forecast Errors)22
nn
Mean Absolute Percent Error (MAPE)Mean Absolute Percent Error (MAPE)
MAPE =MAPE =∑∑100|Actual100|Actualii - Forecast - Forecastii|/Actual|/Actualii
nn
nn
i = 1i = 1
RoundedRounded AbsoluteAbsolute RoundedRounded AbsoluteAbsoluteActualActual ForecastForecast DeviationDeviation ForecastForecast DeviationDeviation
TonnageTonnage withwith forfor withwith forforQuarterQuarter UnloadedUnloaded = .10 = .10 = .10 = .10 = .50 = .50 = .50 = .50
11 180180 175175 5.005.00 175175 5.005.0022 168168 175.5175.5 7.507.50 177.50177.50 9.509.5033 159159 174.75174.75 15.7515.75 172.75172.75 13.7513.7544 175175 173.18173.18 1.821.82 165.88165.88 9.129.1255 190190 173.36173.36 16.6416.64 170.44170.44 19.5619.5666 205205 175.02175.02 29.9829.98 180.22180.22 24.7824.7877 180180 178.02178.02 1.981.98 192.61192.61 12.6112.6188 182182 178.22178.22 3.783.78 186.30186.30 4.304.30
82.4582.45 98.6298.62
RoundedRounded AbsoluteAbsolute RoundedRounded AbsoluteAbsoluteActualActual ForecastForecast DeviationDeviation ForecastForecast DeviationDeviation
TonnageTonnage withwith forfor withwith forforQuarterQuarter UnloadedUnloaded = .10 = .10 = .10 = .10 = .50 = .50 = .50 = .50
11 180180 175175 5.005.00 175175 5.005.0022 168168 175.5175.5 7.507.50 177.50177.50 9.509.5033 159159 174.75174.75 15.7515.75 172.75172.75 13.7513.7544 175175 173.18173.18 1.821.82 165.88165.88 9.129.1255 190190 173.36173.36 16.6416.64 170.44170.44 19.5619.5666 205205 175.02175.02 29.9829.98 180.22180.22 24.7824.7877 180180 178.02178.02 1.981.98 192.61192.61 12.6112.6188 182182 178.22178.22 3.783.78 186.30186.30 4.304.30
82.4582.45 98.6298.62
MAD =∑ |deviations|
n
= 82.45/8 = 10.31For = .10
= 98.62/8 = 12.33For = .50
RoundedRounded AbsoluteAbsolute RoundedRounded AbsoluteAbsoluteActualActual ForecastForecast DeviationDeviation ForecastForecast DeviationDeviation
TonnageTonnage withwith forfor withwith forforQuarterQuarter UnloadedUnloaded = .10 = .10 = .10 = .10 = .50 = .50 = .50 = .50
11 180180 175175 5.005.00 175175 5.005.0022 168168 175.5175.5 7.507.50 177.50177.50 9.509.5033 159159 174.75174.75 15.7515.75 172.75172.75 13.7513.7544 175175 173.18173.18 1.821.82 165.88165.88 9.129.1255 190190 173.36173.36 16.6416.64 170.44170.44 19.5619.5666 205205 175.02175.02 29.9829.98 180.22180.22 24.7824.7877 180180 178.02178.02 1.981.98 192.61192.61 12.6112.6188 182182 178.22178.22 3.783.78 186.30186.30 4.304.30
82.4582.45 98.6298.62MADMAD 10.3110.31 12.3312.33
= 1,526.54/8 = 190.82For = .10
= 1,561.91/8 = 195.24For = .50
MSE =∑ (forecast errors)2
n
RoundedRounded AbsoluteAbsolute RoundedRounded AbsoluteAbsoluteActualActual ForecastForecast DeviationDeviation ForecastForecast DeviationDeviation
TonnageTonnage withwith forfor withwith forforQuarterQuarter UnloadedUnloaded = .10 = .10 = .10 = .10 = .50 = .50 = .50 = .50
11 180180 175175 5.005.00 175175 5.005.0022 168168 175.5175.5 7.507.50 177.50177.50 9.509.5033 159159 174.75174.75 15.7515.75 172.75172.75 13.7513.7544 175175 173.18173.18 1.821.82 165.88165.88 9.129.1255 190190 173.36173.36 16.6416.64 170.44170.44 19.5619.5666 205205 175.02175.02 29.9829.98 180.22180.22 24.7824.7877 180180 178.02178.02 1.981.98 192.61192.61 12.6112.6188 182182 178.22178.22 3.783.78 186.30186.30 4.304.30
82.4582.45 98.6298.62MADMAD 10.3110.31 12.3312.33MSEMSE 190.82190.82 195.24195.24
= 44.75/8 = 5.59%For = .10
= 54.05/8 = 6.76%For = .50
MAPE =∑100|deviationi|/actuali
n
n
i = 1
RoundedRounded AbsoluteAbsolute RoundedRounded AbsoluteAbsoluteActualActual ForecastForecast DeviationDeviation ForecastForecast DeviationDeviation
TonnageTonnage withwith forfor withwith forforQuarterQuarter UnloadedUnloaded = .10 = .10 = .10 = .10 = .50 = .50 = .50 = .50
11 180180 175175 5.005.00 175175 5.005.0022 168168 175.5175.5 7.507.50 177.50177.50 9.509.5033 159159 174.75174.75 15.7515.75 172.75172.75 13.7513.7544 175175 173.18173.18 1.821.82 165.88165.88 9.129.1255 190190 173.36173.36 16.6416.64 170.44170.44 19.5619.5666 205205 175.02175.02 29.9829.98 180.22180.22 24.7824.7877 180180 178.02178.02 1.981.98 192.61192.61 12.6112.6188 182182 178.22178.22 3.783.78 186.30186.30 4.304.30
82.4582.45 98.6298.62MADMAD 10.3110.31 12.3312.33MSEMSE 190.82190.82 195.24195.24MAPEMAPE 5.59%5.59% 6.76%6.76%
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