- The loss of detail involved in this aggregation will lead to a loss of measurability, which presents problems for evaluability of a macro-ToC
- Even where the macro-ToC can be tested the relevance of the results to a specific project could be contested, because individual projects could challenge the macro-ToC as a representation of their project intentions.
Some of these differences will be more worthwhile testing than others, if they cover more projects. For example, in the tree structure above, the difference in "Number of funders" applies to all five projects, whereas the difference in "Geographic scale of project" only applies to two projects. More important differences, that apply to more projects, will also by definition, have more cases that can be compared to each other
It is also possible to identify compound hypotheses worth testing. Participants could be asked to walk down each branch in turn and indicate at each branch point "Which of these types of projects do you think has/will be the most successful?" The combination of project attributes described by a given branch is the configuration of conditions hypothesised to lead to the result predicted.
PS: These thoughts have been prompted by my experience of being involved in a number of macro-evaluations of projects in recent years.