[Orgmode] Estimate ranges in column view

[Mike Gauland]

When planning my work, I estimate the effort required as a range, rather than a
single value. That is, instead of estimating a certain task will take 4 days,
I'll use a range of 3-5 days. If I'm a bit less confident I know how long it
will take, I'll use a wider range (e.g., 2-6 days).  

When I first started doing this, I switched from using a single 'Effort' column
in org mode, to two columns (Effort_Low and Effort_High), simply summing each
column to get an estimate for a composite task.  However, this magnifies the
level of uncertainty in the estimate. The final 'Effort_Low' value tells me what
to expect if everything goes optimally; 'Effort_High' provides the extremely
pessimistic view.

More realistic summaries come from considering the range of each pair, using the
combined statistical variance in each (low, high) pair to determine the variance
in the final value. This is the method used by LiquidPlanner, for example.

I've been mucking about with org-colview.el to automate this calculation for me,
and am quite pleased with the results so far. I've approached this by adding a
new summary type ("est") to org-columns-compile-map, and extending
org-columns-number-to-string and org-columns-string-to-number to convert ranges
to and from strings. This lets me populate an 'Estimates' column with values
such as "[2 4]", and specify a summary type "est" to have the algorithm
described above used to produce the final estimates.

I have two questions for the list:

  1. Is this the right approach, or should I change the behaviour of the
existing EFFORT property?
  2. Is this something others would find useful?

Thanks,
Mike