Windchill Risk and Reliability Desktop Help > Windchill ALT > ALT Interface > ALT Plot Options > Plot Types
Plot Types
As described in ALT Plot Options, the availability of a plot type depends on the type of data set and its parameter values. The following table describes all possible plot types and indicates if they support displaying confidence bounds.
Plot
Description
Confidence Bounds
Probability
Shows the probability of failure (unreliability) line at each stress level (or combination of stress levels) with respect to the time in the transformed scales such that the probability line becomes a straight line. It also shows the data points for each line at the failure times and can include the probability line at use stress levels.
Yes
Reliability vs Time
Shows the reliability function with respect to time (regular scales) at specified usage stress levels.
Yes
Unreliability vs Time
Shows the unreliability function with respect to time (regular scales) at specified usage stress levels.
Yes
PDF Plot
Shows the probability density function (pdf) with respect to time at specified usage stress levels.
No
Failure Rate vs Time
Shows the failure rate, which is also known as the hazard rate, with respect to time at specified usage stress levels.
Yes
Life vs Stress Plot
Shows the life characteristic with respect to a specified stress. It also shows the probability density function (pdf) at each stress level. Other stresses are considered to be fixed at usage stress levels.
• For the Weibull distribution, the life characteristic is η (Eta).
• For the lognormal distribution, the life characteristic is the median, which is equal to exp(mu).
• For the exponential distribution, the life characteristic is η (Eta). MTBF = 1/FR.
Yes
Standard Deviation vs Stress
Shows the standard deviation of the failure time with respect to a specified stress. Other stresses are considered to be fixed at usage stress levels. You use this plot to measure the spread of the data at each stress level.
No
Acceleration Factor vs Stress
Shows the acceleration factor with respect to a specified stress. Other stresses are considered to be fixed at usage stress levels.
Yes
* 
For the next three plots, residual is the difference between the fitted and observed values. You use residual plots to assess model assumptions, reveal inadequacies in the model, and identify extreme observations.
Standardized Residuals Plot
Shows the probability plot of the standardized residuals.
• For the Weibull distribution, standard residuals are plotted on a Gumbel lower probability (smallest extreme value distribution) plot. The standard residual at each observation is defined as:
• For the lognormal distribution, standard residuals for the lognormal distribution are plotted on a normal probability plot. The standard residual at each observation is defined as:
If the distribution adequately describes the data, then the standardized residuals should appear to follow a straight line on the plot. If an observation is suspended (censored), the corresponding residual is also considered to be suspended.
No
Cox-Snell Residuals
Shows Cox-Snell residuals on the exponential probability plot. The standard residual at each observation is defined as:
If the model adequately describes the data, then residuals should follow the exponential distribution with a mean of 1.
No
Standard vs Fitted Value
Shows the standardized residuals versus the scale parameter at each stress level. For this plot, standardized residuals are plotted on log-linear paper with respect to the life characteristic (scale parameter) of the underlying life distribution. The life characteristic is a function of stress.
• For the Weibull distribution, the life characteristic is η (Eta).
• For the lognormal distribution, the life characteristic is the median, which is equal to exp(mu).
• For the exponential distribution, the life characteristic is η (Eta). MTBF = 1/FR.
No
3D Likelihood Function
Shows the likelihood function on the z-axis with respect to two specified model parameters for the x-axis and y-axis.
No
3D Surface Plot
Shows the surface plot of the reliability, failure rate, or probability density function on the z-axis with respect to any combination of two variables that include lifetime or a stress for the x-axis and y-axis. Other stresses are considered to be fixed at usage stress levels. If time is not one of the axes, then it must be specified.
No