Answer:
Unobtrusive measures.
Explanation:
As the name of the term implies, the unobtrusive measures consists in measures that don't require the researcher to intrude in the context of the particular research. Maybe they just observe or analyze from a distance; just as Steve and Naomi: they are counting the empty whiskey bottles in trash cans to measure the level of whiskey consumption in town. They are observing people's behavior who do not know they are being studied.
