Understanding Forecasting
Video tutorial
Forecasting is a method of extrapolating or predicting data based on time. BIRT Analytics forecasting uses the Holt-Winters method, iteratively applying a formula to produce a time series and a forecast. This formula uses a weighted average of data prior to time t to provide a result for time t.
This method consists of three components: the level, trend, and seasonal component.
For example, to forecast the number of orders to be received during the next 12 months, you would perform the following tasks:
 Select the data you wish to observe, the y-axis of the time series.
 Select the time interval for the series, the x-axis of the time series.
Outliers are observations that appear to deviate markedly from other members of the sample in which they occur. When running pre-analysis, values that are more than two standard deviations away from the sample mean are considered outliers. Outliers are replaced by the sample mean. Generally, outliers should be replaced so that they do not bias any projections.
The value of the previous observation replaces any null values encountered in the sample. If the null value encountered is the first observation of the sample, the value of the nearest non-null observation replaces the null value.
How to create and execute a forecast
To get a forecast of the number of orders to be received in the next 12 months, select Parameters and complete the following procedure:
 1 From My Data, drag the Order table and drop it in Measure. Leave the default operation as Count.
 2 Drag the Month column and drop it in Column, in the Dimension area.
 3 To find out if your data contains a seasonal element, select Has seasonality and set Seasonal periodicity to 12. With monthly data, there are 12 observations in each cycle until the seasonal pattern is repeated.
 4 Set other values, as required:
 5 Execute pre-analysis:
 1 To analyze the time series before making a prediction, choose Pre-Analysis.
 2 On Pre-Analysis, analyze the results and decide:
 6 To run the forecast, choose Calculate.
How to use forecasting results
After calculating the results, you can analyze and save the forecast.
 1 On Forecast, analyze the graphical results:
 2 On Table, review the forecasted data and the original data in tabular format. The forecasted values are labeled numerically, starting from 1.
 3 To save the forecasting analysis, choose Save. On Save, you can choose to share the analysis with other BIRT Analytics users.
Video tutorial
Predicting seasonal trends in your data

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