A sociologist plans to study how the clothing Americans wear has become less and less formal over time. To get a sense of how clothing choices have changed over time, the sociologist examines thousands of historical photographs and carefully takes notes about where the photo was taken, when it was taken, and what the people in the photo were wearing. This study is an example of __________?
1) qualitative research
2) probability sampling
3) ethnography
4) empirical generalizations