Seasonality Test in Forecast

[Former Member]

Hello Experts,

I am analyzing what does SAP do for detecting seasonality from the history data.

From the documentation, I can understand that SAP builds Autocorrelation coefficient from the trend eliminated history data. Seasonal test is positive, if this autocorrelation coefficient is greater than 0.3.

I know that Y = mX + b is the formula used for regression line. m is the trend value or slope of this regression line. b is the slope-intercept.

SAP calculates also something called, grundwert or base-value at a point (x,y) where x is the mid of the historical period and y is the average history (mean historical value). Is this called as slope-intercept (b)?

Now my doubts are about how this trend elimination happens:

- What is the formula for building this trend value (m)?

- Is slope-intercept (b) being calculated? If so, what is formula for it?

- And how is the trend eliminated from the history? What is the formula for building the trend eliminated history?

- Why is this grundwert or base-value being calculated? Is it used for building seasonal index? What is its significance?

- I cannot clearly understand the concept of why the autocorrelation coefficient is calculated, what significance it has to do with seasonality determination and seasonal index determination.

Please help me in understanding this. If you find something incorrect, please correct me as well.

Thanks and Best Regards,

Suresh

[Former Member]

Hello Suresh,

Did you manage to find an answer to this question you had? I am searching for the same thing actually, but I haven't been able to find any answer on the web. I would be very interested to hear if you have some findings regarding this.

Regards

/Mattias

[Former Member]

Hi Mattias,

Yup. I understood by debugging the program again. Cannot describe in writing. I have to refresh it again before explaining to you

Best Regards,

Suresh