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 Trend Test

Use

The system performs the trend test as part of automatic model selection . If the trend test is successful, the system selects all forecast strategies that you assigned to the trend test in Customizing. For more information, see the IMG for Advanced Planning and Optimization under Start of the navigation path Supply Chain Planning Next navigation step Service Parts Planning (SPP) Next navigation step Forecasting Next navigation step Configure Automatic Model Selection End of the navigation path .

The trend test checks the demand history of a location product from the last 24 periods for trend behavior. If trend behavior does exists, a trend model would be most suitable as the forecast model for the corresponding location product, for example linear regression or second-order exponential smoothing .

Features

Prerequisites for the Test

The location product must have a demand history of at least 24 periods.

Test Data

The system performs the trend test with the demand after outlier correction. The system thus corrects the outliers that exceed a demand limit. The system calculates this demand limit according to the following formula:

  • The system calculates the average demand from the average of the demand values over the last 24 periods, excluding the highest value.

  • The system calculates the demand deviation from the average of the standard deviation over the last 24 periods, excluding the highest value.

  • You can define the safety coefficient k in the Outlier Correction Parameter for Demand field on the General tab page of the forecast profile. You get to the forecast profile on the SAP Easy Access screen under Start of the navigation path Advanced Planning and Optimization Next navigation step Service Parts Planning (SPP) Next navigation step Planning Next navigation step Forecasting End of the navigation path .

Test

  1. The system plots a straight line through the demand history of the last 24 periods according to the method of the least squares that has either a positive or a negative gradient.

  2. The system plots a horizontal through the demand history of the last 24 periods that corresponds to the average of the demand history of these 24 periods.

  3. The system forms the quotients from the sum of the squared deviations of the lines and the sum of the squared deviations of the horizontals.

  4. The system repeats steps one to three using the demand history of the last 12 periods.

  5. The system compares the quotients, which the system has calculated based on the demand history of the last 24 periods, with your entry in the forecast profile on the Test tab page in the Threshold for 24 Periods in Trend Test field.

  6. The system compares the quotients, which the system has calculated based on the demand history of the last 12 periods, with your entry in the forecast profile on the Test tab page in the Threshold for 12 Periods in Trend Test field.

The trend test is successful is the following conditions are met:

  • The quotient that the system formed based on the demand history of the last 24 periods is greater than your entry in the Threshold Value for 24 Periods in Trend Test field.

  • The quotient that the system formed based on the demand history of the last 12 periods is greater than your entry in the Threshold Value for 12 Periods in Trend Test field.

  • The gradient of the line over 24 periods of the demand history and the gradient of the line over 12 periods of the demand history is the same. This means that the gradient of the two lines is either rising or falling.

If the trend test for a location product was successful but you already use a trend model for forecasting this location product, the system uses the values in the Stability Threshold for 24 Periods in Trend Test and the Stability Threshold for 12 Periods in Trend Test fields instead of the values in the Threshold for 24 Periods in Trend Test and Stability Threshold for 12 Periods in Trend Test fields.

Replace Trend Test

To replace the trend test with a test you have defined yourself, you can implement the Business Add-In (BAdI) BAdI: Modify Trend Test (/SAPAPO/PFCS_FCST_TRENDTEST).