Randy beat me to it, I was about to post a methodology on how to track mite invasion. However, it is harsh and not many would adhere to such a protocol:

The weekly invasion of bee hives by Varroa jacobsoni [sic] was recorded using colonies containing Bayvarol-strips. Each monitor colony was 2 fold overdosed using 8 strips, each containing 3.6 mg flumethrin. To maintain the acaricide efficacy the carriers were replaced by new ones every 8th week.

In 1987, 3 monitor colonies were always placed in 2 apiaries. In 1988, 2 colonies were placed in 5 apiaries, one colony placed in between the row of infested colonies (=In), the other at a distance of approx 10 m (=Out).

Sheets fitting the hive bottom exactly were used to collect the dead mites from the colony. The sheets were spread with Vaseline and covered by 2 x 2 mm gauze net to prevent bees from carrying out dead mites.

Dead mites were counted weekly on the sheets. In 1988, the infested colonies in the apiaries were treated at the end of the observation period using Bayvarol-strips and dead mites were recorded.

Numbers of mites differed over a wide range between monitor colonies in the same apiary, and 
*** no difference was apparent in relation to their position within the row of colonies (In) or apart (Out). ***

[comments: Several investigators have suggested that keeping bees in apiaries encourages mite invasion, but this work seems to invalidate that suggestion. On the other hand, isolated colonies may be less prone to being robbed than colonies in apiaries, or marauding bees may preferentially seek larger groups of hives]

Source:
Sakofski, F., N. Koeniger, and S. Fuchs. "Seasonality of honey bee colony invasion by Varroa jacobsoni Oud." Apidologie 21.6 (1990): 547-550.

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