Interpretation of the TTT plot

• A plot around the diagonal indicates constant failure rate function, i.e., exponentially distributed time-to-failures
• A concave plot (above the diagonal) indicates increasing failure rate function(IFR)
• A convex plot indicates decreasing failure rate function (DFR)
• A plot that is first convex, and then concave, indicates the "bath curve"
• A plot that is first concave, and then convex, indicates hetrogenity in the data