Which of the following distribution represents the time estimates in PERT ?

Explanation

Concept: Beta Distribution: Beta distribution in case PERT is a 3- times estimation viz. optimistic time (t o), most likely time (t m) and pessimistic time (t p) to calculate the expected duration of the particular activity. The normal distribution cannot describe unsymmetrical conditions while Beta distribution explainsboth symmetric and un-symmetric patterns. The probability distribution of activity duration may be symmetric or un- symmetric, hence Beta distribution is the best choice for describing the expected duration of an activity. Expected duration of activity (t E) = mean of beta distribution Important Points Poisson’s distribution: A Poisson distribution is a tool that helps to predict the probability of certain events from happening when you know how often the events have occurred . Poisson distribution is a limiting form of the binomial distribution . It is close to zero because it measures a number of defects ( which is already defective ). Ex. Defective fan Here the reason for defectiveness may be any i.e. it may be a capacitor, coils, etc. It gives the probability of a given number of events happening in a fixed interval of time . In queuing theory, it is used where the number of arrival per unit time will follow the Poisson distribution. Normal Distribution: According to the central limit, theorem samples may be following any type of distribution but the universe or population will follow Normal distribution. Similarly, project activity will follow Beta distribution but the project will follow Normal distribution. Project duration dist ribution = where, μ = Critical path duration, σ = Standard deviation of critical path Weibull distribution: μ ± 3σ The Weibull probability distribution can be used as an alternative model for task time estimates in the PERT estimating methodology . It has the same advantage as the traditional Beta distribution for this application.