Civil Engineering MCQAE Level Civil Engineering

The Weibull plotting position formula assigns a probability P to the m-th ranked value (ascending order) in a data series of N values as:

HydrologyWeibull Plotting PositionMEDIUM

Choose the correct answer

A

P = m / N

B

P = m / (N + 1)

C

P = (m - 0.375) / (N + 0.25)

D

P = (m - 0.5) / N

Correct Answer

B. P = m / (N + 1)

Why is this the answer?

Weibull: P = m/(N+1), where m = rank (1 = smallest). Return period T = 1/P = (N+1)/m. Weibull is unbiased estimator of exceedance probability. Other formulas: Hazen P = (m-0.5)/N; Blom (Gringorten) P = (m-0.44)/(N+0.12) (better for extreme value distributions).

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