Estimating

• Estimating approaches

  Parametic

  Analogous

  Analytical

  Delphi
• Paramedic estimating

  uses the statistical relationship between variables to estimate project parameters

  uses historical data and mathematical models to determine the relationship between variables, size, duration and cost

  eg is you know that a painter can paint 5 meter sq in 1 hour, you can use that to estimate the time needed to paint a wall
• Benefits of Parametic

  Produces estimates quickly, can estimate areas of multiple project simultaneously
• Issues with Parametic

  relies on previous mathematical and historical data relating to similar project being correct and easily accessible
• Analogous

  uses similar projects to make a comparison to estimate

  eg if you had a similar project that took 6 months and 5 main developer, you would suggest that with 6 developers it will take less than 6 months
• analogous benefits

  useful if you don't have detailed historical or mathematical data, and good for initial estimates
• analogous issues

  not very precise as its just a comparison
• analytical

  breaks down the project into smaller tasks and then estimates each one based on specific requirements, constraints or characteristics eg budget limitations, available resources for that stage, complexity of work
• analytical benefits

  very detailed, allows for a more precise budget and plan to be made for each specific stage
• analytical issues

  very time consuming, may require experts
• delphi

  gets a group of experts to estimate anonymously then they are collected, summarized and repeated until a consensus is made
• delphi benefits


  helps eliminate any bias based on individual experience or opinion, is very accurate
• delphi issues

  relies on having a diverse group of experts to begin with, it is time consuming as it takes multiple rounds
• reasons for re estimating

  Changes to the scope- eg working on a construction project and the client decides they want 2 more bedrooms- you need to re estimate budget, schedule and resources

  Unexpected delays or challenges- eg about to fit the specific flooring but its out of stick- you need to re estimate based on delivery time and new material cost or look at using new supplier

  New information- eg new safety regulations based on ladder safety- have to re estimate to keep up with regulations eg needing a second man for all roofing work
• benefits of re estimating

  helps the project stay on track- as they progress new information emerges and re estimating means you can account for the changes whilst staking on track - it means you can pro actively address deviations and make the correct adjustment

  helps with managing stakeholders by providing more accurate and up to date info on time/costs

  allows for better resource allocation- eg if a task took up more material than estimated you will change the allocation in the next iteration, also helps to utilize resources if you have spare
• challenges of re estimating

  requires additional time not only at the start of the project but also throughout

  can disrupt project momentum and potentially lead to the project plan being adjusted and scope changed which then takes time to be approved

  can cause setbacks form stakeholders if they dont agree with the re estimations or understand why the changes are necessary- highlights the need for detailed stakeholder communication