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Copyright ©2011 Pearson Education 16-1 Chapter 16 Time-Series Forecasting Statistics for Managers using Microsoft Excel 6 th Global Edition
Copyright ©2011 Pearson Education 16-2 Learning Objectives In this chapter, you learn: About different time-series forecasting models: moving averages, exponential smoothing, linear trend, quadratic trend, exponential trend, autoregressive models, and least squares models for seasonal data To choose the most appropriate time-series forecasting model
Copyright ©2011 Pearson Education 16-3 The Importance of Forecasting Governments forecast unemployment rates, interest rates, and expected revenues from income taxes for policy purposes Marketing executives forecast demand, sales, and consumer preferences for strategic planning College administrators forecast enrollments to plan for facilities and for faculty recruitment Retail stores forecast demand to control inventory levels, hire employees and provide training DCOVA
Copyright ©2011 Pearson Education 16-4 Common Approaches to Forecasting Used when historical data are unavailable Considered highly subjective and judgmental Common Approaches to Forecasting Causal Quantitative forecasting methods Qualitative forecasting methods Time Series Use past data to predict future values DCOVA
Copyright ©2011 Pearson Education 16-5 Time-Series Data Numerical data obtained at regular time intervals The time intervals can be annually, quarterly, monthly, weekly, daily, hourly, etc. Example: Year: Sales: DCOVA
Copyright ©2011 Pearson Education 16-6 Time-Series Plot the vertical axis measures the variable of interest the horizontal axis corresponds to the time periods A time-series plot is a two-dimensional plot of time series data DCOVA
Copyright ©2011 Pearson Education 16-7 Time-Series Components Time Series Cyclical Component Irregular Component Trend Component Seasonal Component Overall, persistent, long- term movement Regular periodic fluctuations, usually within a 12-month period Repeating swings or movements over more than one year Erratic or residual fluctuations DCOVA
Copyright ©2011 Pearson Education 16-8 Upward trend Trend Component Long-run increase or decrease over time (overall upward or downward movement) Data taken over a long period of time Sales Time DCOVA
Copyright ©2011 Pearson Education 16-9 Downward linear trend Trend Component Trend can be upward or downward Trend can be linear or non-linear Sales Time Upward nonlinear trend Sales Time (continued) DCOVA
Copyright ©2011 Pearson Education Seasonal Component Short-term regular wave-like patterns Observed within 1 year Often monthly or quarterly Sales Time (Quarterly) Winter Spring Summer Fall Winter Spring Summer Fall DCOVA
Copyright ©2011 Pearson Education Cyclical Component Long-term wave-like patterns Regularly occur but may vary in length Often measured peak to peak or trough to trough Sales 1 Cycle Year DCOVA
Copyright ©2011 Pearson Education Irregular Component Unpredictable, random, “residual” fluctuations Due to random variations of Nature Accidents or unusual events “Noise” in the time series DCOVA
Copyright ©2011 Pearson Education Does Your Time Series Have A Trend Component? A time series plot should help you to answer this question. Often it helps if you “smooth” the time series data to help answer this question. Two popular smoothing methods are moving averages and exponential smoothing. DCOVA
Copyright ©2011 Pearson Education Smoothing Methods Moving Averages Calculate moving averages to get an overall impression of the pattern of movement over time Averages of consecutive time series values for a chosen period of length L Exponential Smoothing A weighted moving average DCOVA
Copyright ©2011 Pearson Education Moving Averages Used for smoothing A series of arithmetic means over time Result dependent upon choice of L (length of period for computing means) Last moving average of length L can be extrapolated one period into future for a short term forecast Examples: For a 5 year moving average, L = 5 For a 7 year moving average, L = 7 Etc. DCOVA
Copyright ©2011 Pearson Education Moving Averages Example: Five-year moving average First average: Second average: etc. (continued) DCOVA
Copyright ©2011 Pearson Education Example: Annual Data YearSales etc… etc… DCOVA
Copyright ©2011 Pearson Education Calculating Moving Averages Each moving average is for a consecutive block of 5 years YearSales Average Year 5-Year Moving Average …… etc… DCOVA
Copyright ©2011 Pearson Education Annual vs. Moving Average The 5-year moving average smoothes the data and makes it easier to see the underlying trend DCOVA
Copyright ©2011 Pearson Education Exponential Smoothing Used for smoothing and short term forecasting (one period into the future) A weighted moving average Weights decline exponentially Most recent observation is given the highest weight DCOVA
Copyright ©2011 Pearson Education Exponential Smoothing The weight (smoothing coefficient) is W Subjectively chosen Ranges from 0 to 1 Smaller W gives more smoothing, larger W gives less smoothing The weight is: Close to 0 for smoothing out unwanted cyclical and irregular components Close to 1 for forecasting (continued) DCOVA
Copyright ©2011 Pearson Education Exponential Smoothing Model Exponential smoothing model where: E i = exponentially smoothed value for period i E i-1 = exponentially smoothed value already computed for period i - 1 Y i = observed value in period i W = weight (smoothing coefficient), 0 < W < 1 For i = 2, 3, 4, … DCOVA
Copyright ©2011 Pearson Education Exponential Smoothing Example Suppose we use weight W = 0.2 Time Period (i) Sales (Y i ) Forecast from prior period (E i-1 ) Exponentially Smoothed Value for this period (E i ) etc etc etc. 23 (.2)(40)+(.8)(23)=26.4 (.2)(25)+(.8)(26.4)=26.12 (.2)(27)+(.8)(26.12)= (.2)(32)+(.8)(26.296)= (.2)(48)+(.8)(27.437)= (.2)(48)+(.8)(31.549)= (.2)(33)+(.8)(31.840)= (.2)(37)+(.8)(32.872)= (.2)(50)+(.8)(33.697)= etc. E 1 = Y 1 since no prior information exists DCOVA
Copyright ©2011 Pearson Education Sales vs. Smoothed Sales Fluctuations have been smoothed NOTE: the smoothed value in this case is generally a little low, since the trend is upward sloping and the weighting factor is only.2 DCOVA
Copyright ©2011 Pearson Education Forecasting Time Period i + 1 The smoothed value in the current period (i) is used as the forecast value for next period (i + 1) : DCOVA
Copyright ©2011 Pearson Education Exponential Smoothing in Excel Use data analysis / exponential smoothing The “damping factor” is (1 - W) DCOVA
Copyright ©2011 Pearson Education There Are Three Popular Methods For Trend-Based Forecasting Linear Trend Forecasting Nonlinear Trend Forecasting Exponential Trend Forecasting DCOVA
Copyright ©2011 Pearson Education Linear Trend Forecasting Estimate a trend line using regression analysis Year Time Period (X) Sales (Y) Use time (X) as the independent variable: In least squares linear, non-linear, and exponential modeling, time periods are numbered starting with 0 and increasing by 1 for each time period. DCOVA
Copyright ©2011 Pearson Education Linear Trend Forecasting The linear trend forecasting equation is: Year Time Period (X) Sales (Y) (continued) DCOVA
Copyright ©2011 Pearson Education Linear Trend Forecasting Forecast for time period 6 (2010): Year Time Period (X) Sales (y) ?? (continued) DCOVA
Copyright ©2011 Pearson Education Nonlinear Trend Forecasting A nonlinear regression model can be used when the time series exhibits a nonlinear trend Quadratic form is one type of a nonlinear model: Compare adj. r 2 and standard error to that of linear model to see if this is an improvement Can try other functional forms to get best fit DCOVA
Copyright ©2011 Pearson Education Exponential Trend Model Another nonlinear trend model: Transform to linear form: DCOVA
Copyright ©2011 Pearson Education Exponential Trend Model Exponential trend forecasting equation: where b 0 = estimate of log(β 0 ) b 1 = estimate of log(β 1 ) (continued) Interpretation: is the estimated annual compound growth rate (in %) DCOVA
Copyright ©2011 Pearson Education Trend Model Selection Using Differences Use a linear trend model if the first differences are approximately constant Use a quadratic trend model if the second differences are approximately constant DCOVA
Copyright ©2011 Pearson Education Use an exponential trend model if the percentage differences are approximately constant (continued) Trend Model Selection Using Differences DCOVA
Copyright ©2011 Pearson Education Autoregressive Modeling Used for forecasting Takes advantage of autocorrelation 1st order - correlation between consecutive values 2nd order - correlation between values 2 periods apart p th order Autoregressive model: Random Error DCOVA
Copyright ©2011 Pearson Education Autoregressive Model: Example Year Units The Office Concept Corp. has acquired a number of office units (in thousands of square feet) over the last eight years. Develop the second order Autoregressive model. DCOVA
Copyright ©2011 Pearson Education Autoregressive Model: Example Solution Year Y i Y i-1 Y i Excel Output Develop the 2nd order table Use Excel to estimate a regression model DCOVA
Copyright ©2011 Pearson Education Autoregressive Model Example: Forecasting Use the second-order equation to forecast number of units for 2010: DCOVA
Copyright ©2011 Pearson Education Autoregressive Modeling Steps 1.Choose p (note that df = n – 2p – 1) 2.Form a series of “lagged predictor” variables Y i-1, Y i-2, …,Y i-p 3.Use Excel or Minitab to run regression model using all p variables 4.Test significance of A p If null hypothesis rejected, this model is selected If null hypothesis not rejected, decrease p by 1 and repeat DCOVA
Copyright ©2011 Pearson Education Choosing A Forecasting Model Perform a residual analysis Eliminate a model that shows a pattern or trend Measure magnitude of residual error using squared differences and select the model with the smallest value Measure magnitude of residual error using absolute differences and select the model with the smallest value Use simplest model Principle of parsimony DCOVA
Copyright ©2011 Pearson Education Residual Analysis Random errors Trend not accounted for Cyclical effects not accounted for Seasonal effects not accounted for T T T T ee e e DCOVA
Copyright ©2011 Pearson Education Measuring Errors Choose the model that gives the smallest measuring errors Mean Absolute Deviation (MAD) Less sensitive to extreme observations Sum of squared errors (SSE) Sensitive to outliers DCOVA
Copyright ©2011 Pearson Education Principal of Parsimony Suppose two or more models provide a good fit for the data Select the simplest model Simplest model types: Least-squares linear Least-squares quadratic 1st order autoregressive More complex types: 2nd and 3rd order autoregressive Least-squares exponential DCOVA
Copyright ©2011 Pearson Education Time series are often collected monthly or quarterly These time series often contain a trend component, a seasonal component, and the irregular component Suppose the seasonality is quarterly Define three new dummy variables for quarters: Q 1 = 1 if first quarter, 0 otherwise Q 2 = 1 if second quarter, 0 otherwise Q 3 = 1 if third quarter, 0 otherwise (Quarter 4 is the default if Q 1 = Q 2 = Q 3 = 0) Forecasting With Seasonal Data DCOVA
Copyright ©2011 Pearson Education Exponential Model with Quarterly Data Transform to linear form: (β 1 –1)x100% is the quarterly compound growth rate β i provides the multiplier for the i th quarter relative to the 4th quarter (i = 2, 3, 4) DCOVA
Copyright ©2011 Pearson Education Estimating the Quarterly Model Exponential forecasting equation: where b 0 = estimate of log(β 0 ), so b 1 = estimate of log(β 1 ), so etc… Interpretation: = estimated quarterly compound growth rate (in %) = estimated multiplier for first quarter relative to fourth quarter = estimated multiplier for second quarter rel. to fourth quarter = estimated multiplier for third quarter relative to fourth quarter DCOVA
Copyright ©2011 Pearson Education Quarterly Model Example Suppose the forecasting equation is: b 0 = 3.43, so b 1 =.017, so b 2 = -.082, so b 3 = -.073, so b 4 =.022, so DCOVA
Copyright ©2011 Pearson Education Quarterly Model Example Interpretation: Unadjusted trend value for first quarter of first year 4.0% = estimated quarterly compound growth rate Average sales in Q 1 are 82.7% of average 4 th quarter sales, after adjusting for the 4% quarterly growth rate Average sales in Q 2 are 84.5% of average 4 th quarter sales, after adjusting for the 4% quarterly growth rate Average sales in Q 3 are 105.2% of average 4 th quarter sales, after adjusting for the 4% quarterly growth rate Value: (continued) DCOVA
Copyright ©2011 Pearson Education Pitfalls in Time-Series Analysis Assuming the mechanism that governs the time series behavior in the past will still hold in the future Using mechanical extrapolation of the trend to forecast the future without considering personal judgments, business experiences, changing technologies, and habits, etc. DCOVA
Copyright ©2011 Pearson Education Chapter Summary Discussed the importance of forecasting Addressed component factors of the time-series model Performed smoothing of data series Moving averages Exponential smoothing Described least square trend fitting and forecasting Linear, quadratic and exponential models
Copyright ©2011 Pearson Education Chapter Summary Addressed autoregressive models Described procedure for choosing appropriate models Addressed time series forecasting of monthly or quarterly data (use of dummy variables) Discussed pitfalls concerning time-series analysis (continued)
Copyright ©2011 Pearson Education On Line Topic Index Numbers Statistics for Managers using Microsoft Excel 6 th Edition
Copyright ©2011 Pearson Education Learning Objective In this On Line Topic you learn about price indexes and differences between aggregated and disaggregated indexes
Copyright ©2011 Pearson Education Index Numbers Index numbers allow relative comparisons over time Index numbers are reported relative to a Base Period Index Base period index = 100 by definition Used for an individual item or group of items DCOVA
Copyright ©2011 Pearson Education Simple Price Index Simple Price Index: where I i = index number for year i P i = price for year i P base = price for the base year DCOVA
Copyright ©2011 Pearson Education Index Numbers: Example Airplane ticket prices from 1995 to 2003: YearPrice Index (base year = 2006) Base Year: DCOVA
Copyright ©2011 Pearson Education Prices in 2000 were 90% of base year prices Prices in 2006 were 100% of base year prices (by definition, since 2006 is the base year) Prices in 2009 were 120% of base year prices Index Numbers: Interpretation DCOVA
Copyright ©2011 Pearson Education Aggregate Price Indexes An aggregate index is used to measure the rate of change from a base period for a group of items Aggregate Price Indexes Unweighted aggregate price index Weighted aggregate price indexes Paasche IndexLaspeyres Index DCOVA
Copyright ©2011 Pearson Education Unweighted Aggregate Price Index Unweighted aggregate price index formula: = unweighted price index at time t = sum of the prices for the group of items at time t = sum of the prices for the group of items in time period 0 i = item t = time period n = total number of items DCOVA
Copyright ©2011 Pearson Education Unweighted total expenses were 18.8% higher in 2009 than in 2006 Automobile Expenses: Monthly Amounts ($): YearLease paymentFuelRepair Total Index (2001=100) Unweighted Aggregate Price Index: Example DCOVA
Copyright ©2011 Pearson Education Weighted Aggregate Price Indexes Paasche index : weights based on : weights based on current period 0 quantities period quantities = price in time period t = price in period 0 Laspeyres index DCOVA
Copyright ©2011 Pearson Education Common Price Indexes Consumer Price Index (CPI) Producer Price Index (PPI) Stock Market Indexes Dow Jones Industrial Average S&P 500 Index NASDAQ Index DCOVA
Copyright ©2011 Pearson Education Topic Summary Learned about price indexes and differences between aggregated and disaggregated indexes
Copyright ©2011 Pearson Education All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.
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