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The following sections describe the minimum data requirements for using different folios in Weibull++. This includes:
Depending on the data type and the number of failures and/or suspensions present within your data, Weibull++ can perform all or some of the available analyses and calculations in a standard folio. Note that data sets with 2 or more distinct failure times, with or without suspensions, can be calculated with any of the available distributions, except for the mixed Weibull distribution.
For the mixed Weibull distribution, the following requirements apply:
At least 5 unique failure times (i.e., data points with different time values) are required for the 2-subpopulation analysis.
At least 8 unique failure times are required for the 3-subpopulation analysis.
At least 11 unique failure times are required for the 4-subpopulation analysis.
In addition, Weibull++ allows you to work with data sets that have fewer than 2 distinct failures. However, the analysis methods that can be performed will vary depending on the data and particular case.
There are a total of five possible cases as to how data can be entered. For each scenario, a description of the available analysis options is provided in this appendix:
The minimum data requirements for degradation analysis folios are as follows:
The unit ID must be entered for all data points.
For all models except Gompertz, there must be at least 2 data points for each unique unit ID. For the Gompertz model, there must be at least 3 data points for each unique unit ID.
The data must produce enough extrapolated failure/suspension times to perform life data analysis with the selected life distribution. See the requirements for standard folios.
For non-parametric LDA folios, there must be at least 1 data point entered.
Weibull++ provides four data formats for warranty analysis. The requirements for each format are described next.
The minimum data requirements for warranty analysis folios in the Nevada chart format are as follows:
The returns quantity cannot exceed the sales quantity.
At least one data point must be entered.
With only Sales data entered (i.e., a data set with suspensions only), only the 1-parameter Weibull or 1-parameter exponential distributions with maximum likelihood estimation (MLE) will be available. To use the 1-parameter Weibull, you will be prompted to enter the beta value and the lower one-sided confidence bound. Confidence bounds will not be available in the QCP or plots. This is similar to Case 2 for standard folios.
If the Returns data contains failure(s) for only 1 time period, only MLE analysis is possible. In addition, the 3-parameter Weibull, mixed Weibull and generalized gamma distributions will not be available. This is similar to Case 4 for standard folios.
If the Returns data contains failure(s) for at least 2 time periods, all distributions except mixed Weibull will be available. This is similar to Case 5 for standard folios.
The minimum data requirements for warranty analysis folios in the times-to-failure format are the same as those described previously for standard folios, except you cannot calculate with no data entered.
The minimum data requirements for warranty analysis folios in the dates of failure format are as follows:
The "End of Observation Period" (entered on the Main page of the control panel) is required.
The "Date In-Service" is required for all Sales and Returns data points. Each date entered in the Returns sheet must be identical to a date that has been entered in the Sales sheet.
At least one data point must be entered.
With only Sales data entered (i.e. a data set with suspensions only), only the 1-parameter Weibull or 1-parameter exponential distributions with maximum likelihood estimation (MLE) will be available. To use the 1-parameter Weibull, you will be prompted to enter the beta value and the lower one-sided confidence bound. Confidence bounds will not be available in the QCP or plots. This is similar to Case 2 for standard folios.
If the Returns data contains only one unique failure point, only MLE analysis is possible. In addition, the 3-parameter Weibull, mixed Weibull and generalized gamma distributions will not be available. This is similar to Case 4 for standard folios.
If the Returns data contains failure(s) for at least two time periods, all distributions except mixed Weibull will be available. This is similar to Case 5 for standard folios.
The minimum data requirements for warranty analysis folios in the usage format are the same as those described above for warranty folios in the dates of failure format.
The minimum data requirements for event log folios are as follows:
The system start date must be earlier than or the same as the earliest event date.
At least one event must be entered.
The minimum data requirements for parametric recurrent RDA folios are as follows:
The System ID must be entered for all data points.
There must be at least 3 unique Failure (F) data points entered.
The minimum data requirements for non-parametric RDA folios are as follows:
The System ID must be entered for all data points.
If confidence bounds are not required, there must be at least 1 Failure (F) data point for each unique System ID.
If confidence bounds are required, there must be at least 2 unique System IDs with at least 1 Failure (F) data point each.
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