Example of warranty prediction
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You work for an appliance manufacturer and must use current warranty data to predict the number of refrigerator compressor warranty claims you expect to see over the next five months.

1    Open the worksheet COMPRESSOR.MTW.

2    Choose Stat > Reliability/Survival > Warranty Analysis > Pre-Process Warranty Data.

3    In Shipment (sale) column, enter Ship.

4    In Return (failure) columns, enter Month1-Month12. Click OK.

5    Choose Stat > Reliability/Survival > Warranty Analysis > Warranty Prediction.

6    In Start time, enter 'Start time'. In End time, enter 'End time'. In Frequency (optional), enter Frequencies.

7    Click Prediction. In Production quantity for each time period, enter 1000. Click OK in each dialog box.

Session window output

Pre-Process Warranty Data: Shipment = Ship, Returns = Month1, Month2, ...

 

 

 

 

Warranty Prediction: Start = Start time and End = End time

 

 

* NOTE * 22 cases were used; 2 cases contained missing values or zero

         frequencies.

 

 

Using frequencies in Frequencies

 

 

Distribution: Weibull with shape = 1.26494, scale = 398.062

Estimation method: Maximum likelihood

 

 

Summary of Current Warranty Claims

 

Total number of units                            12000

Observed number of failures                      69

Expected number of failures                      68.5201

95% Poisson CI                                   (53.2630, 86.7876)

 

Number of units at risk for future time periods  11931

 

 

Production Schedule

 

Future time period      1     2     3     4     5

Production quantity  1000  1000  1000  1000  1000

 

 

Table of Predicted Number of Failures

 

Future  Potential  Predicted

  Time  Number of  Number of   95% Poisson CI

Period   Failures   Failures    Lower    Upper

     1      12931    13.1073   7.0000  22.3660

     2      13931    27.4930  18.1933  39.8678

     3      14931    43.1798  31.2722  58.1271

     4      15931    60.1892  45.9516  77.4449

     5      16931    78.5416  62.1373  97.9488

Graph window output

Interpreting the results

You can see from the summary of current warranty claims that, of 12000 units in the field during the data collection period, 69 compressors failed. Using the Weibull distribution to model time-to-failure, approximately 69 units were expected to fail.

From the table of predicted number of failures and the predicted number of failures plot, you can conclude with 95% confidence that between approximately 62 and 98 more units are expected to fail in the next five months.