Follow-Up & Survival Analysis Flashcards
7 cards from real CET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Follow-Up & Survival Analysis flashcards as text
In the Weibull distribution, a shape parameter β > 1 indicates:
Answer: Increasing failure rate (wear-out)
When β > 1, the Weibull hazard function increases over time, which is characteristic of wear-out failures.
What does the scale parameter η (eta) represent in the Weibull distribution?
Answer: The time at which exactly 63.2% of units have failed
η is the characteristic life; at t = η, the cumulative failure fraction is always 1 − 1/e ≈ 63.2% regardless of β.
When β = 1 in the Weibull distribution, it simplifies to which distribution?
Answer: Exponential distribution
At β = 1, the Weibull hazard function becomes constant, making it identical to the exponential distribution.
On a Weibull probability plot, the slope of the best-fit line estimates which parameter?
Answer: The shape parameter β
The slope of the line on a Weibull probability plot directly estimates the shape parameter β.
The cumulative hazard function H(t) is related to the survival function S(t) by:
Answer: H(t) = −ln[S(t)]
By definition S(t) = e^(−H(t)), so rearranging gives H(t) = −ln[S(t)].
Which test is most commonly used to compare the survival curves of two independent groups?
Answer: Log-rank test
The log-rank test compares overall survival distributions between groups and handles censored data correctly.
In a reliability block diagram, series-connected components produce a system reliability that is:
Answer: Less than the lowest individual component reliability
All series components must work simultaneously, so the system reliability is the product of individual reliabilities and is lower than any single component.