Four quarters method

To perform the four quarters method, we follow these steps ... 

The MAPE is a good measure of forecast error when the underlying forecast has significant seasonality and demand varies considerably from one period to the next Consider a scenario in which two methods are used to make quarterly forecasts for a product with seasonal demand that peaks in the third quarter. Method 1 returns forecast errors of 190, 200, 245, and 180 Method 2 returns forecast errors of 100,120,500, and 100 over four quarters. Method 1 has a lower MSE and MAD relative to Method 2 and would be preferred if either alterion was used. If demand is highly seasonal, however, and averages 1,000, 1,200, 4,800, and 1,100 in the four periods. Method 2 results in a MAPE of 9.9 percent, whereas Method 1 resnlts in a mnch higher MAPE, 14.3 percent. In this instance, it can be argued that Method 2 should be preferred to Method 1. 

We composite or homogenize samples using a procedure, which is often referred to as the four quarters or the quartering method. The required equipment consists of a stainless steel pan or a tray and a stainless steel spoon or a scoop. To eliminate the need for decontamination between samples, these inexpensive supplies may be discarded after each sample. 

The remaining calculations are shown in Table 2.8 using a spreadsheet. Comparing the forecast of Example 2.6 (Holt s method) and Example 2.7 (Winters method), we note that the forecasts are the same for the first four quarters (2008). However, they are different from 2009 onward due to the updating of the seasonality indices. The forecast for the first quarter of 2011 is given by... 

Consider Example 2.7 where Winters method was used to forecast the demand for the first quarter of 2011. Determine the demand forecasts all four quarters of 2011. 

At this stage, we have estimated the level, trend, and all seasonal factors. We can now obtain the forecast for the next four quarters using Equation 7.1. In the example, the forecast for the next four periods using the static forecasting method is given by... 

The team compiles the error estimates for the four forecasting methods as shown in Table 7-2. Based on the error information in Table 7-2, the forecasting team decides to use Winter s model. It is not surprising that Winter s model results in the most accurate forecast, because the demand data have both a growth trend as well as seasonality. Using Winter s model, the team forecasts the following demand for the coming four quarters ... 

The zero in the eontrol-to-output eharaeteristie eaused by the ESR of the output filter eapaeitor ean be found by two methods if the value of the aetual ESR is known from the eapaeitor s data sheet, then the loeation of the zero ean be ealeulated, if not, it ean be grossly estimated. Using four aluminum eleetrolytie eapaeitors in parallel should eut the total ESR to one-quarter that exhibited by eaeh. I will estimate the zero to be at 10 KHz. 

Progress Rept No 12, April-June 30, 1956. In this final quarterly progress rept period, it. was hoped that comprehensive data could be accumulated and presented on the "probe method of temp of deton determination for NG, Tetryl and PETN. However, delivery of Textronix oscilloscopes was slow and the condition of two of the four units made them unusable on arrival. 

Another common method of separating the Elements of Water is called a Seven-fold distillation or 4x3 distillation. The fermented water is first distilled gently into four equal volumes. The first quarter to distil is labelled as Fire of Water. The second quarter is labelled as Air of Water. Next comes the Water Element followed by Earth. Again, the distillation is stopped before dryness and the residue is dried then labelled as the Gur. 

Using an in situ lysis method, Gutierrez et al. [20] electrophoretically surveyed sixty-five halobacterial strains for the presence of large plasmids. Three quarters of the strains had plasmids visible by this method, the majority containing three or four [20]. Due to the limitations of the electrophoretic technique used, this analysis no doubt missed some of the largest plasmids (such as the largest Haloferax volcanii plasmid [15]). 

Powdered material is poured into a cone and divided into four equal parts. One quarter is recovered and the process was repeated until the required weight of sample is obtained. This method is prone to operator bias, as finer particles tend to remain in the center of the cone because of size segregation. Symmetry of the cone is also quite difficult to achieve but is necessary for accuracy, so this method is not recommended. ... 

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