Final answer:
Mary Pattillo's study on black professionals in a Chicago neighborhood primarily utilized observational field research to gather detailed qualitative data.
Step-by-step explanation:
Mary Pattillo primarily used observational field research to study the influx of black professionals into a Chicago neighborhood where many lower-class blacks already lived. This method allowed her to collect rich, qualitative data through direct observation and to capture the social dynamics and interactions within the community in detail. Ethnographic field research is conducive to understanding complex social phenomena, like the one Pattillo was investigating, as it provides deeper insights into participants' behaviors, attitudes, and experiences within their natural context.