Here is my reply. The short version of the reply is: yes, I believe some methods are effective, but if there is a lot of unpredictability, it is better to just track what happens and then extrapolate from the results. The catch is that the variance that causes unpredictability does not necessarily arise from within the project. That makes the effects hard to predict, and difficult to control.
Expounding on this a bit further: in The Variance Trap series I have modeled projects as systems standing in isolation. This is a huge simplification. In real life, there is a lot of interaction between the project system, and other systems. A typical development team, consisting of a number of consultants (that's typical in my line of work) will be influenced by:
- Groups within the teams own organisation, with their own agendas. This includes their own management. (There are some examples in my reply to Scott.)
- Team members will have their own agendas.
- If the team members come from different organizations, each one of those will influence the project. (They do it whether they want to or not. For example, if one team member comes from an organization that does not use automated tests and version management systems, that may have quite an impact on the overall performance of the team.)
- The customer's organization is not homogenous. It consists of a lot of groups. each one of those may have their own agendas.
- The world outside may influence the project. Have you ever had a project finish successfully (you think), and then dropped because a competing product has just hit the market? Legislation often affects a project. A legislative change can be the reason for starting a project, but it can also stop one. Cultural bias definitely affects projects. Our culture is steeped in the doctrines of Scientific Management and Cost Accounting, which is perhaps the most important reason why software projects fail so often. One reason why accountants are disliked within many companies, is that they often give very bad advice about how to run the company. (Upper management believes them, but nobody else does.) They do this because they base their recommendations on Cost Accounting. Cost Accounting is a mathematical model of a company that was proven not to work more than 20 years ago. Companies are still required by law to use it. (They may use other accounting methods internally, but many don't.)