ExpForecast

Syntax

ExpForecast(Year1, Value1, Year2, Value2,... YearN, ValueN) or
ExpForecast(ExcelFile, ExcelRange)
ExpForecast(LCDS, SeriesName, Filter1, Filter2, [CountryISO3])
ExpForecast(Branch:Variable)
ExpForecast(FirstYear, LastYear)

See also: Using Time-Series Functions and Specifying Excel File and Range Parameters, ExpForecastBY.

Summary

Forecasts future values based on an exponential regression of historical data. 

The second syntax of the function retrieves years and values from a specified Excel file and range. The third syntax of the function retries years and values from the online LEAP Cloud Data Server (LCDS). In both cases, retrieving this data initially may takes some time (typically a second or less depending on your internet connection), but thereafter values are cached locally for near-instant retrieval.  Use the Time-Series wizard to help specify the parameters required when using these syntaxes.

Description

Exponential forecasting is used to estimate future values based on a time series of historical data. The new values are predicted using linear regression to an exponential growth model (Y = m + X^c) where the Y terms corresponds to the variableData that can change over time. to be forecast and the X term is years. Exponential forecasting is most useful in cases where certain values can be expected to grow at constant growth rates over the period in question (e.g. population levels).

Use this function with caution. You may need to first use a spreadsheet or some other package to test the statistical validity of the forecast (i.e. test how well the regression "fits" the historical data). You can also use the LEAP's built-in statistical functions such as RSquared, StandardError, and Observations to help with this task.  The Time-series Wizard will also diplay these basic statsical parameters. Bear in mind that future values may be markedly different from historical ones, particular if structural or policy shifts in the economy such as changing energy policies are likely to have an impact on future trends.

Typically, you will enter this function in your Current Accounts data and use it to forecast values for a scenario. The function will also forecast values for the Current Accounts period. If you wish to return actual values for the Current Accounts period use the ExpForecastCA function.

The syntax ExpForecast(FirstYear, LastYear) is a special syntax that can only be used in scenarios (not in Current Accounts).  This syntax generates a forecast in a scenario based on the data in Current Accounts.  Only the values between and including FirstYear and LastYear are used as input to the regression that generates the forecast.  FirstYear must be on or after the base year. LastYear must be before the first scenario year. LastYear must be at least three years after FirstYear.