Other forms of research

Experiments
The benefits of experiments are that you can provide proof.
Drawbacks, too expensive to do a  large ammount of research.


Participant observation
The researcher can go further into depth of the certain group they are studying.
The drawbacks of participant observation are that the researcher may change their behaviour, biased opinion.

Historical research
The benefits of this are that you can see how it worked compared to how it worked in the past.
The drawbacks are that with time things change so your research may not be much use now.

Rhetorical analysis

analysis of the techniques used to persuade the audience.
persuasive language encourages people to buy something. It can be wrong if phrased incorrectly.

Comparative analysis
The benefits of comparative analysis gives a fuller view of the market, what you're up against, what you need to be better than and different from.

Competitor analysis