forecasting demand

A demand forecast is the prediction of what will happen to your company's existing product sales. It would be best to determine the demand forecast using a multi-functional approach. The inputs from sales and marketing, finance, and production should be considered. The final demand forecast is the consensus of all participating managers. You may also want to put up a Sales and Operations Planning group composed of representatives from the different departments that will be tasked to prepare the demand forecast.

Determination of the demand forecasts is done through the following steps:

• Determine the use of the forecast

• Select the items to be forecast

• Determine the time horizon of the forecast

• Select the forecasting model(s)

• Gather the data

• Make the forecast

• Validate and implement results

There are two approaches to determine demand forecast – (1) the qualitative approach, (2) the quantitative approach. The comparison of these two approaches is shown below:

Qualitative Approach
Quantitative Approach
Used when situation is vague & little data exist (e.g., new products and technologies)
Used when situation is stable & historical data exist
(e.g. existing products, current technology)
Involves intuition and experience
Involves mathematical techniques
Jury of executive opinion
Sales force composite
Delphi method
Consumer market survey
Time series models
Causal models

Qualitative Forecasting Methods

Your company may wish to try any of the qualitative forecasting methods below if you do not have historical data on your products' sales.

Qualitative Method
Jury of executive opinion
The opinions of a small group of high-level managers are pooled and together they estimate demand. The group uses their managerial experience, and in some cases, combines the results of statistical models.
Sales force composite
Each salesperson (for example for a territorial coverage) is asked to project their sales. Since the salesperson is the one closest to the marketplace, he has the capacity to know what the customer wants. These projections are then combined at the municipal, provincial and regional levels.
Delphi method
A panel of experts is identified where an expert could be a decision maker, an ordinary employee, or an industry expert. Each of them will be asked individually for their estimate of the demand. An iterative process is conducted until the experts have reached a consensus.
Consumer market survey
The customers are asked about their purchasing plans and their projected buying behavior. A large number of respondents is needed here to be able to generalize certain results.

Quantitative Forecasting Methods

There are two forecasting models here – (1) the time series model and (2) the causal model. A time series is a s et of evenly spaced numerical data and is o btained by observing responses at regular time periods. In the time series model , the forecast is based only on past values and assumes that factors that influence the past, the present and the future sales of your products will continue.

On the other hand, t he causal model uses a mathematical technique known as the regression analysis that relates a dependent variable (for example, demand) to an independent variable (for example, price, advertisement, etc.) in the form of a linear equation. The time series forecasting methods are described below:

Time Series Forecasting Method
Naïve Approach
Assumes that demand in the next period is the same as demand in most recent period; demand pattern may not always be that stable
For example:

If July sales were 50, then Augusts sales will also be 50

Time Series Forecasting Method
Moving Averages (MA)
MA is a series of arithmetic means and is used if little or no trend is present in the data; provides an overall impression of data over time
A simple moving average uses average demand for a fixed sequence of periods and is good for stable demand with no pronounced behavioral patterns.

F 4 = [D 1 + D2 + D3] / 4

F – forecast, D – Demand, No. – Period
(see illustrative example – simple moving average)
A weighted moving average adjusts the moving average method to reflect fluctuations more closely by assigning weights to the most recent data, meaning, that the older data is usually less important. The weights are based on intuition and lie between 0 and 1 for a total of 1.0
WMA 4 = (W) (D3) + (W) (D2) + (W) (D1)
WMA – Weighted moving average, W – Weight, D – Demand, No. – Period
(see illustrative example – weighted moving average)

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