Question: Which of these sentences is better?

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> * The **method to** measure the intelligence of a man is to...
> * The **method for** estimating the intelligence of a man is to...
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Is it *method to* or *method for*?

Answer: 
I don't know of any concrete rules, but "method of" or "method for" would seem more natural to me and are the usual constructions I see. 

The only time I can recall "method to" being used is in "method to (his or her) madness," where method is to mean "purpose" more than "process." 

Sources:

* The five APA style papers on my desk that all have a Methodology section and use one of the above phrasings. For what it's worth, "Method of" was used eight times, "method for" two times, and "method to" zero times.
* In the physical sciences and mathematics, methods are typically named as "Method of *\_*\_." E.g., Method of Exhaustion, Method of Images, Method of Coordination, Method of Infinite Descent, Method of Successive Frames.
the word'to' indicates intention / purpose.

When we say, 
Students study to gain knowledge.
We are making parallel two entities which are parallel
i.e. (noun + verb) before 'to' and (noun+verb) after 'to'
*We mean that 'studying' is done for the purpose of gaining knowledge.*

But when we say 'The method to measure the intelligence.....'
we are trying to make parallel two non-parallel entities.
i.e 'method' (a noun) is being made parallel to 'measure' (a verb)....... this is neither good and nor preferable.