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SMA 6304 / MIT / MIT Manufacturing Systems Lecture 11: Forecasting Lecturer: Prof. Duane S. Boning Copyright 2003 © Duane S. Boning. 1

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Agenda 1.Regression Polynomial regression Example (using Excel) 2.Time Series Data & Regression Autocorrelation –ACF Example: white noise sequences Example: autoregressive sequences Example: moving average ARIMA modeling and regression 3.Forecasting Examples Copyright 2003 © Duane S. Boning. 2

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Copyright 2003 © Duane S. Boning. 3 Regression –Review&Extensions Single Model Coefficient: Linear Dependence Slope and Intercept (or Offset): Polynomial and Higher Order Models: Multiple Parameters Key point: linear regression can be used as long as the model is linear in the coefficients (doesnt matter the dependence in theindependent variable)

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Copyright 2003 © Duane S. Boning. 4 Polynomial Regression Example Replicate data provides opportunity to check for lack of fit

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Copyright 2003 © Duane S. Boning. 5 Growth Rate –First Order Model Mean significant, but linear term not Clear evidence of lack of fit

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Copyright 2003 © Duane S. Boning. 6 Growth Rate –Second Order Model No evidence of lack of fit Quadratic term significant

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Copyright 2003 © Duane S. Boning. 7 Polynomial Regression In Excel Create additional input columns for each input Use Data Analysis and Regression tool

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Copyright 2003 © Duane S. Boning. 8 Polynomial Regression

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Copyright 2003 © Duane S. Boning. 9 Agenda 1.Regression Polynomial regression Example (using Excel) 2.Time Series Data & Time Series Regression Autocorrelation –ACF Example: white noise sequences Example: autoregressive sequences Example: moving average ARIMA modeling and regression 3.Forecasting Examples

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Copyright 2003 © Duane S. Boning. 10 Time Series –Time as an Implicit Parameter Data is often collected with a time-order An underlying dynamic process (e.g. due to physics of a manufacturing process) may create autocorrelation in the data

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Copyright 2003 © Duane S. Boning. 11 Intuition: Where Does Autocorrelation Come From? Consider a chamber with volume V, and with gas flow in and gas flow out at rate f. We are interested in the concentration x at the output, in relation to a known input concentration w.

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Copyright 2003 © Duane S. Boning. 12 Key Tool: Autocorrelation Function (ACF) Time series data: time index i CCF: cross-correlation function ACF: auto-correlation function

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Copyright 2003 © Duane S. Boning. 13 Stationary vs. Non-Stationary Stationary series: Process has a fixed mean

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Copyright 2003 © Duane S. Boning. 14 White Noise –An Uncorrelated Series Data drawn from IID gaussian ACF: We also plot the 3σlimits – values within these not significant Note that r(0) = 1 always (a signal is always equal to itself with zero lag – perfectly autocorrelated at k = 0) Sample mean Sample variance

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Copyright 2003 © Duane S. Boning. 15 Autoregressive Disturbances Generated by: Mean Variance

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Copyright 2003 © Duane S. Boning. 16 Another Autoregressive Series Generated by: High negativeautocorrelation Slow drop in ACF with large αBut now ACF alternates in sign

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Copyright 2003 © Duane S. Boning. 17 Random Walk Disturbances Generated by: Mean Variance

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Copyright 2003 © Duane S. Boning. 18 Moving Average Sequence Generated by: Mean Variance

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Copyright 2003 © Duane S. Boning. 19 ARMA Sequence Generated by: Both AR & MA behavior

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Copyright 2003 © Duane S. Boning. 20 ARIMA Sequence Start with ARMA sequence Add Integrated (I) behavior

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Copyright 2003 © Duane S. Boning. 21 Periodic Signal with Autoregressive Noise Original Signal After Differencing

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Copyright 2003 © Duane S. Boning. 22 Agenda 1. Regression Polynomial regression Example (using Excel) 2. Time Series Data & Regression Autocorrelation –ACF Example: white noise sequences Example: autoregressive sequences Example: moving average ARIMA modeling and regression 3. Forecasting Examples

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Copyright 2003 © Duane S. Boning. 23 Cross-Correlation: A Leading Indicator Now we have two series: –An input or explanatory variable x –An output variable y CCF indicates both AR and lag:

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Copyright 2003 © Duane S. Boning. 24 Regression & Time Series Modeling The ACF or CCF are helpful tools in selecting an appropriate model structure – Autoregressive terms? xi= αxi-1 – Lag terms? yi= γxi-k One can structure data and perform regressions – Estimate model coefficientvalues, significance, and confidence intervals – Determine confidence intervals on output – Check residuals

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Copyright 2003 © Duane S. Boning. 25 Statistical Modeling Summary 1. Statistical Fundamentals Sampling distributions Point and interval estimation Hypothesis testing 2. Regression ANOVA Nominal data: modeling of treatment effects (mean differences) Continuous data: least square regression 3. Time Series Data & Forecasting Autoregressive, moving average, and integrative behavior Auto-and Cross-correlation functions Regression and time-series modeling

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