Lesson08_new

Slide 1: 

Lesson 8-1 Statistics for Management Session 8 Time-Series Analysis

Lesson Topics : 

Lesson Topics Component Factors of the Time-Series Model Smoothing of Data Series Moving Averages Exponential Smoothing Least Square Trend Fitting and Forecasting Linear, Quadratic and Exponential Models Autoregressive Models Choosing Appropriate Models Monthly or Quarterly Data

What Is Time-Series : 

What Is Time-Series A Quantitative Forecasting Method to Predict Future Values Numerical Data Obtained at Regular Time Intervals Projections Based on Past and Present Observations Example: Year: 1994 1995 1996 1997 1998 Sales: 75.3 74.2 78.5 79.7 80.2

1. Time-Series Components : 

1. Time-Series Components Time-Series Cyclical Random Trend Seasonal

Trend Component : 

Trend Component Overall Upward or Downward Movement Data Taken Over a Period of Years Sales Time Upward trend

Cyclical Component : 

Cyclical Component Upward or Downward Swings May Vary in Length Usually Lasts 2 - 10 Years Sales Time Cycle

Seasonal Component : 

Seasonal Component Upward or Downward Swings Regular Patterns Observed Within 1 Year Sales Time (Monthly or Quarterly) Winter

Random or Irregular Component : 

Random or Irregular Component Erratic, Nonsystematic, Random, ‘Residual’ Fluctuations Due to Random Variations of Nature Accidents Short Duration and Non-repeating

Multiplicative Time-Series Model : 

Multiplicative Time-Series Model Used Primarily for Forecasting Observed Value in Time Series is the product of Components For Annual Data: For Quarterly or Monthly Data: Ti = Trend Ci = Cyclical Ii = Irregular Si = Seasonal

2. Moving Averages : 

2. Moving Averages Used for Smoothing Series of Arithmetic Means Over Time Result Dependent Upon Choice of L, Length of Period for Computing Means For Annual Time-Series, L Should be Odd Example: 3-year Moving Average First Average: Second Average:

Moving Average Example : 

Moving Average Example Year Units Moving Ave 1994 2 NA 1995 5 3 1996 2 3 1997 2 3.67 1998 7 5 1999 6 NA John is a building contractor with a record of a total of 24 single family homes constructed over a 6 year period. Provide John with a Moving Average Graph.

Moving Average Example Solution : 

Moving Average Example Solution Year Response Moving Ave 1994 2 NA 1995 5 3 1996 2 3 1997 2 3.67 1998 7 5 1999 6 NA 94 95 96 97 98 99 8 6 4 2 0 Sales

3. Exponential Smoothing : 

3. Exponential Smoothing Weighted Moving Average Weights Decline Exponentially Most Recent Observation Weighted Most Used for Smoothing and Short Term Forecasting Weights Are: Subjectively Chosen Ranges from 0 to 1 Close to 0 for Smoothing Close to 1 for Forecasting

Exponential Weight: Example : 

Exponential Weight: Example Year Response Smoothing Value Forecast (W = .2) Ei 1994 2 2 NA 1995 5 (.2)(5) + (.8)(2) = 2.6 2 1996 2 (.2)(2) + (.8)(2.6) = 2.48 2.6 1997 2 (.2)(2) + (.8)(2.48) = 2.384 2.48 1998 7 (.2)(7) + (.8)(2.384) = 3.307 2.384 1999 6 (.2)(6) + (.8)(3.307) = 3.846 3.307

Exponential Weight: Example Graph : 

Exponential Weight: Example Graph 94 95 96 97 98 99 8 6 4 2 0 Sales Year Data Smoothed

4. The Linear Trend Model : 

4. The Linear Trend Model Year Coded Sales 94 0 2 95 1 5 96 2 2 97 3 2 98 4 7 99 5 6 Projected to year 2000

The Quadratic Trend Model : 

The Quadratic Trend Model Year Coded Sales 94 0 2 95 1 5 96 2 2 97 3 2 98 4 7 99 5 6

The Exponential Trend Model : 

The Exponential Trend Model or Excel Output of Values in logs Year Coded Sales 94 0 2 95 1 5 96 2 2 97 3 2 98 4 7 99 5 6

5. Autogregressive Modeling : 

5. Autogregressive Modeling Used for Forecasting Takes Advantage of Autocorrelation 1st order - correlation between consecutive values 2nd order - correlation between values 2 periods apart Autoregressive Model for pth order: Random Error

Autoregressive Model: Example : 

Autoregressive Model: Example The Office Concept Corp. has acquired a number of office units (in thousands of square feet) over the last 8 years. Develop the 2nd order Autoregressive models. Year Units 92 4 93 3 94 2 95 3 96 2 97 2 98 4 99 6

Autoregressive Model: Example Solution : 

Autoregressive Model: Example Solution Year Yi Yi-1 Yi-2 92 4 --- --- 93 3 4 --- 94 2 3 4 95 3 2 3 96 2 3 2 97 2 2 3 98 4 2 2 99 6 4 2 Develop the 2nd order table run a regression model

Autoregressive Model Example: Forecasting : 

Autoregressive Model Example: Forecasting Use the 2nd order model to forecast number of units for 2000:

Autoregressive Modeling Steps : 

Autoregressive Modeling Steps 1. Choose p: Note that df = n - 2p - 1 2. Form a series of “lag predictor” variables Yi-1 , Yi-2 , … Yi-p 3. Use SPSS to run regression model using all p variables 4. Test significance of Ap If null hypothesis rejected, this model is selected If null hypothesis not rejected, decrease p by 1 and repeat

6. Selecting A Forecasting Model : 

6. Selecting A Forecasting Model Perform A Residual Analysis Look for pattern or direction Measure Sum Square Errors - SSE (residual errors) Measure Residual Errors Using MAD Use Simplest Model Principle of Parsimony

Measuring Errors : 

Measuring Errors Sum Square Error (SSE) Mean Absolute Deviation (MAD)

Principal of Parsimony : 

Principal of Parsimony Suppose 2 or more models provide good fit for data Select the Simplest Model Simplest model types: least-squares linear least-square quadratic 1st order autoregressive More complex types: 2nd and 3rd order autoregressive least-squares exponential

Lesson Summary : 

Lesson Summary Discussed 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 Addressed Autoregressive Models Described Procedure for Choosing Appropriate Models Discussed Seasonal Data (use of dummy variables)