Answer:
A Retrospective Study.
Explanation:
A retrospective study is demonstrated as the kind of observational study that aims to examine the outcomes or changes observed over a span of time.
As per the question, the given problem statement demonstrates 'a retrospective study'(kind of observational study) as it aims to observe the 'viewing habits of households over a span of 7years of time' in order to determine the number of households remained tuned to a specific news program and if it increased or not. Thus, it justifies the above definition and hence, a retrospective study is the correct answer.