Weibull Parameter Estimation using Linear Regression

weibull01 Weibull Parameter Estimation using Linear RegressionWeibull statistic is the most favorite model of mine. Not only its flexibility to mimic many natural phenomenon, it also has plenty of methods (approaches) in predicting its parameters. Yes, I do like the choices of Weibull in deciding which parameter estimation method suits with my application. In this writing, I want to show the example of Linear Regression method in predicting 2-parameters Weibull distribution. Other methods such as Maximum Likelihood or Percentile will be discussed later on.

2-parameter Weibull model can be expressed as

(Equation 1). image003 Weibull Parameter Estimation using Linear Regression

Where as:

image006 Weibull Parameter Estimation using Linear Regression = time
image009 Weibull Parameter Estimation using Linear Regression= scale parameter
image012 Weibull Parameter Estimation using Linear Regression= shape parameter
image015 Weibull Parameter Estimation using Linear Regression = constant 2.71828…

Equation (1) can be converted into linear form by taking the log of the equation twice. This process results the following equation.

(Equation 2). image017 Weibull Parameter Estimation using Linear Regression

which can be considered as linear as

(Equation 3). image020 Weibull Parameter Estimation using Linear Regression

where
Y = image022 Weibull Parameter Estimation using Linear Regression
X = image025 Weibull Parameter Estimation using Linear Regression
a = image028 Weibull Parameter Estimation using Linear Regression
b = image012 Weibull Parameter Estimation using Linear Regression

Estimating a and b in equation 3 be solved using linear regression as follow

image032 Weibull Parameter Estimation using Linear Regression

image034 Weibull Parameter Estimation using Linear Regression

The question is how to predict F(t) which is the cumulative distribution of data. For ranked data, some approaches have been suggested using the following formulas

image036 Weibull Parameter Estimation using Linear Regression

The example of the first method above is as follow. If we have series of failure data in minutes 2, 3, 5, 8, 20, 50, the image038 Weibull Parameter Estimation using Linear Regression for the first data (2 minutes) is (1-0.5)/6 = 0.083. Completely, that series of failure data have the series of image038 Weibull Parameter Estimation using Linear Regressionas 0.083, 0.25, 0.417, 0.583, 0.750, and 0.917. This series of image038 Weibull Parameter Estimation using Linear Regressionthen become the predictor for image038 Weibull Parameter Estimation using Linear Regression in equation (2).

Software like Spreadsheet (ex: MS Excell) has capability to estimate Weibull parameter using linear regression method. An example of its usage shown in the following figure..

weib excel Weibull Parameter Estimation using Linear Regression

Download the excel file

Some criticisms have been addressed to Linear Regression method in predicting 2-parameter Weibull model. However, due to its simplicity, this method has been widely used in many applications. I do prefer this method if the accuracy that I need does not ask me sophisticated method such as Maximum Likelihood, etc.

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Schlagworte: distribusi weibull, Estimation, Linear, Parameters, Regression, Statistics, Weibull,