After a fruitful discussion on the last meeting of Limited WIP Society Cologne (http://lwscologne.wordpress.com/), I’d like to summarize some terms:
Often planning and estimation (and analysis) is used interchangeably, but this yields to confusion and stress:
Estimation is the act of determining values based on uncertain data. Usually, thought as predicting some future result.
Analysis is the act of breaking something into parts to get a better understanding of it. If you ask a software architect to estimate, he’ll most likely start an analysis and provides some complexity measure (e.g. in function/story points). If you force him to convert the result into person days, then he’ll estimate a factor he applies to the result.It’s a good idea to not ask him to convert into person days. Rather let the factor be based on historical data.
Planning is an act of arranging tasks to fulfill a management target. A plan is never wrong, but has some probability to hit the target. To determine the probability you need an estimation.