Forecasting 246074 220345361 2008-06-19T12:08:59Z 87.183.181.156 +de {{wiktionary|forecast}} {{wiktionary|predict}} '''Forecasting''' is the process of [[estimation]] in unknown situations. [[Prediction]] is a similar, but more general term. Both can refer to estimation of [[time series]], [[cross-sectional data|cross-sectional]] or [[longitudinal study|longitudinal]] data. Usage can differ between areas of application: for example in [[hydrology]], the terms "forecast" and "forecasting" are sometimes reserved for estimates of values at certain specific [[future]] times, while the term "prediction" is used for more general estimates, such as the number of times floods will occur over a long period. [[Risk]] and [[uncertainty]] are central to forecasting and prediction. Forecasting is used in the practice of [[Customer Demand Planning]] in every day business forecasting for manufacturing companies. The discipline of demand planning, also sometimes referred to as supply chain forecasting, embraces both statistical forecasting and a consensus process. Forecasting is commonly used in discussion of time-series data. ==Categories of forecasting methods== ===Time series methods=== [[Time series]] methods use historical data as the basis of estimating future outcomes. *[[Moving average]] *[[Exponential smoothing]] *[[Extrapolation]] *[[Linear prediction]] *[[Trend estimation]] *[[Growth curve]] *Topics ===Causal / econometric methods=== Some forecasting methods use the assumption that it is possible to identify the underlying factors that might influence the variable that is being forecast. For example, sales of umbrellas might be associated with weather conditions. If the causes are understood, projections of the influencing variables can be made and used in the forecast. *[[Regression analysis]] using [[linear regression]] or [[non-linear regression]] *[[Autoregressive moving average model|Autoregressive moving average (ARMA)]] *[[Autoregressive integrated moving average|Autoregressive integrated moving average (ARIMA)]] :e.g. [[Box-Jenkins]] *[[Econometrics]] ===Judgemental methods=== Judgemental forecasting methods incorporate intuitive judgements, opinions and [[probability]] estimates. *[[Composite forecasts]] *[[Statistical survey|Surveys]] *[[Delphi method]] *[[Scenario building]] *[[Technology forecasting]] *[[Forecast by analogy]] ===Other methods=== *[[Simulation]] *[[Prediction market]] *[[Probabilistic forecasting]] and [[Ensemble forecasting]] *[[Reference class forecasting]] ==Forecasting accuracy== The forecast error is the difference between the actual value and the forecast value for the corresponding period. <math>\ E_t = Y_t - F_t </math> where E is the forecast error at period t, Y is the actual value at period t, and F is the forecast for period t. Measures of aggregate error: {| class=wikitable |Mean Absolute Error (MAE) |<math>\ MAE = \frac{\sum_{t=1}^{N} |E_t|}{N} </math> |- |[[Mean Absolute Percentage Error]] (MAPE) |<math>\ MAPE = \frac{\sum_{t=1}^N |\frac{E_t}{Y_t}|}{N} </math> |- |Percent Mean Absolute Deviation (PMAD) |<math>\ PMAD = \frac{\sum_{t=1}^{N} |E_t|}{\sum_{t=1}^{N} |Y_t|} </math> |- |[[Mean squared error]] (MSE) |<math>\ MSE = \frac{\sum_{t=1}^N {E_t^2}}{N} </math> |- |Root Mean squared error (RMSE) |<math>\ RMSE = \sqrt{\frac{\sum_{t=1}^N {E_t^2}}{N}} </math> |} Please note that the business forecasters and demand planners in the industry refer to the PMAD as the MAPE, although they compute this volume weighted MAPE. Difference between MAPE and WMAPE is explained in [[Calculating Demand Forecast Accuracy]] '''See also''' *[[Forecast error]] *[[Calculating Demand Forecast Accuracy]] *[[Predictability]] *[[Prediction interval]], similar to [[confidence interval]] ==Applications of forecasting== Forecasting has application in many situations: *[[Supply chain management]] *[[Weather forecasting]], [[Flood forecasting]] and [[Meteorology]] *[[Transport planning]] and [[Transportation forecasting]] *[[Economic forecasting]] *[[Technology forecasting]] *[[Earthquake prediction]] *[[Land use forecasting]] *[[Product forecasting]] *[[PECOTA|Player and team performance in sports]] *[[Telecommunications forecasting]] ==External links== *[http://www.forecastingprinciples.com Forecasting Principles: ''"Evidence-based forecasting"''] * [http://http://www.itl.nist.gov/div898/handbook/pmc/section4/pmc4.htm Introduction to Time series Analysis (Engineering Statistics Handbook)] - A practical guide to Time series analysis and forecasting *[http://www.statsoft.com/textbook/sttimser.html Time Series Analysis] *[http://www.appliedforecasting.com Applied Forecasting: news on forecasting] *[http://www.ifs.du.edu Global Forecasting with IFs] ==See also== <div style="-moz-column-count:2; column-count:2;"> * [[Calculating Demand Forecast Accuracy]] * [[CPFR]] * [[Foresight (future studies)]] * [[Futures studies]] * [[Futurology]] * [[Optimism bias]] * [[Planning]] * [[Prediction]] * [[Reference class forecasting]] * [[Strategic foresight]] * [[Technology forecasting]] </div> ==References== <references /> *{{cite book |author = [[Armstrong, J. Scott]] (ed.) |title= ''Principles of forecasting: a handbook for researchers and practitioners |date= 2001 |publisher= Kluwer Academic Publishers |location= Norwell, Massachusetts |language= [[English language|English]] |id= ISBN 0-7923-7930-6 }} *{{cite book | author=Geisser, Seymour | authorlink =Seymour Geisser | title = Predictive Inference: An Introduction | date = 1 June 1993 | publisher = Chapman & Hall, CRC Press | language = [[English language|English]] | id = ISBN 0-412-03471-9 }} *{{cite book | author=Makridakis, Spyros | coauthors=Wheelwright, Steven; [http://www.robhyndman.info Hyndman, Rob J] | title= [http://www.robhyndman.info/forecasting/ Forecasting: methods and applications] | date=1998 | publisher = John Wiley & Sons | location = New York | language = [[English language|English]] | id= ISBN 0-471-53233-9 }} *{{cite book |author = Kress, George J. |coauthors= Snyder, John |title= ''Forecasting and market analysis techniques: a practical approach |date= 30 May 1994 |publisher= Quorum Books |location= Westport, Connecticut, London |language= [[English language|English]] |id= ISBN 0-89930-835-X }} *{{cite book | author=Rescher, Nicholas | authorlink =Nicholas Rescher | title = Predicting the future: An introduction to the theory of forecasting | date = 1998 | publisher = State University of New York Press | language = [[English language|English]] | id = ISBN 0791435539 }} *[[Peter Turchin|Turchin, P.]], 2007. Scientific Prediction in Historical Sociology. [http://edurss.ru/cgi-bin/db.pl?cp=&page=Book&id=53185&lang=en&blang=en&list=Found History & Mathematics: Historical Dynamics and Development of Complex Societies.] Moscow: KomKniga. ISBN 5484010020 [[Category:Data analysis]] [[Category:Estimation theory]] [[Category:Time series analysis]] [[de:Vorhersage#Betriebswirtschaft]] [[simple:Forecasting]] [[zh:預測]]