Estimating in project management is an issue that we believe deserves attention as legal initiative that may be a base for official proposals and taxation for services. Let’s check some examples.

Within the Water Holiday Company booking system, there is a transaction that records the final payment made by a customer who has already booked a holiday and paid a deposit. The details of the payment come from an external function that deals with payments by debit and credit cards. The key data items input are an account number, an amount and a date. The system checks that an account exists for the account number and, if it does not, issues an error message (see Table 6.1). Otherwise the new payment is recorded, and the amount paid on the account record is updated. A notification of the new amount outstanding on the account is issued.

Table 6.1 Example of COSMIC function point counting

What does a CFP count really mean? It was suggested above that it is an index value that gives an idea of the amount of processing carried out by the transaction.

We can use a CFP count to find out the relative productivity of development projects that have already been completed. We may find that the average number of CFPs implemented per day is around five. This may seem a rather small number, but ‘development effort’ here includes the whole development cycle, from requirements gathering to testing. When a new project proposal comes along, a preliminary investigation may suggest that the delivered system would have a count of about 250 CFPs. The estimated effort is therefore in the region of 250/5 days – that is, 50 days.


The FSM approach (and, indeed, the more generic approach of using size drivers and productivity rates) is based on the assumption that we have the details of the size driver values and actual effort of past projects. Often, however, such records do not exist. For smaller organisations particularly, the IT projects that have been previously implemented may all seem to have their own peculiarities. For example, some may have involved the installation of vendor-supplied applications, some may have required specially written software, some a mixture of the two, and so on. This seems to suggest that previous experience is not a stable basis for estimating the effort for new projects. However, in this kind of situation the analogy, or comparative, approach could be used.

The main steps with this method are as follows:

  1. Identify the key characteristics of the new project.
  2. Search for a previous project which has similar characteristics.
  3.  Use the actual effort recorded for the previous project as the base estimate for the new one.
  4. Identify the key differences between the old and the new projects (it is unlikely that the old project is an exact match for the new one).
  5. Adjust the base estimate to take account of the identified differences.

An analogy approach can be used to create a top-down estimate for a project. Where there is no past project that seems to be a useful analogy for the new project, an estimator can use analogy to select parts of old projects that seem similar to components of the current project (using analogy as part of a bottom-up approach).

An analogy approach can be used to create a top-down estimate for a project. Where there is no past project that seems to be a useful analogy for the new project, an estimator can use analogy to select parts of old projects that seem similar to components of the current project (using analogy as part of a bottom-up approach).

As Table 6.2 shows, both analogy and the parametric approaches can be used either at the overall level of a project or for estimating the effort needed for components. The activity-based approach – breaking down the overall task into smaller components – seems almost by definition to be a bottom-up approach.

Table 6.2 Relationship between top-down/bottom-up and the three main estimating approaches


As a project planner you may often need to use the effort estimates produced by experts from technical areas in which you are not knowledgeable. Are there any ways in which you can realistically review these estimates? It may be possible to assess the plausibility of the estimates by asking the estimator the questions below.

What methods were used to produce the estimates?

How is the relative size of the job measured (in other words, what are the size/effort drivers)?
How much effort was assumed would be required for each unit of the size driver (in other words, what productivity rates are you assuming)?• Can a past project of about the same size be identified which had about the same effort?
If a job with a comparable size cannot be identified, can past jobs which had similar productivity rates be found?

As you see from these examples estimating in project management practices is important for legal issues for both contractors and customers. The BVOP suggests in their project management certification program that all these practices to be formally checked and agreed.



Staff have managed to develop information systems at a rate of five function points per staff day. A new system has been assessed as requiring 120 CFPs to implement, but the staff available are relatively inexperienced and are only 80 per cent as productive as the staff usually used in such projects.

1. An under-estimate of effort is MOST likely to lead to which of the following?

a. decreased productivity

b. decreased quality

c. a less competitive bid for a contract

d. a longer project duration

2. Which of the following estimating methods is MOST likely to be used bottom-up?

a. parametric

b. algorithmic

c. Delphi

d. activity-based

3. In the XYZ scenario, which one of the following is 80 per cent?

a. a size driver

b. an effort driver

c. a productivity rate

d. a productivity driver

4. In the XYZ scenario, what would be the best estimate of effort for the project?

a. 30 days

b. 25 days

c. 24 days

d. 20 days



The work breakdown structure (or possibly the product breakdown structure).


Among the activities that may need to be carried out are:

  • Create/agree job descriptions.
  • Create job advertisements.
  • Collect and assess applications and curricula vitae (CVs) from potential employees.
  • Invite selected candidates for interview.
  • Interview candidates.
  • Notify successful and unsuccessful candidates.
  • Request, await and check references.
  • Confirm appointment.
  • Arrange induction.
  • Carry out induction processes.

This set of activities offers some good illustrations of the difference between elapsed time and effort. There will be some points – for example, when you are waiting for references – where little effort is expended but time will be passing. provides extended and advanced agile project management course so all these phases and project estimating values can be carefully handled even by junior project managers. No excuses here for anyone.

Actually we advise you that all estimates and outcomes to be validated by a good project management certification policy. has a great list of valuable project management certification resources.

The following are suitable answers:

  1. The number of functions that users need to be able to use.
  2. The number of different types of system user (as each will need to be interviewed for their requirements), and the number of different operations carried out in the system.
  3. The number of functions to be tested and the number of input and output data items to be tested.
  4. The number of different functions in the system, the number of inputs, outputs and tables accessed.


The size driver would be the distance driven to work.

The productivity rate would be the average speed of the car (for example, miles per hour).

We have already suggested that the weather and the amount of traffic congestion could have an effect on the travel time. In this case, the weather and traffic do not increase the size of the job to be done – the distance to work remains the same. These factors are best seen as influences on the productivity rate. In order to assess more accurately the time it takes me to go to work, I could take account of these intermittent constraints on my speed. I may be aware, for instance, that the rush-hour traffic in the morning tends to be significantly less heavy during school holidays. I could therefore perhaps allow myself to start off to work a few minutes later when it is half-term. On the other hand, I may start earlier if it is foggy, as I know that this can slow down the traffic.

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