What are the differences between bottomup and topdown estima

What are the differences between bottom-up and top-down estimating approaches? Determine advantages and disadvantages for using each approach. Under what conditions would you prefer one over the other? Provide a specific example to support your response.

Solution

There is no doubt both are the popular techniques used in project management for the cost estimation. There are both plus and negatives of both the techniques and its use has to be clearly prioritized. The main difference being bottom up is very accurate but takes a lot of time. whereas top down technique is less time consuming but not at all or very minutely accurate. The other difference being bottom up cost estimation is based on thorough estimation of the entire project where each and every element of WBS is estimated seperately. Generally bottom up appraoch is used in most of the situations where accuracy matters a lot like in consulting business where there are a lot of deliverables. Top down estimate gives fast results and is preferable in construction projects where deliveerables are limited or few.