The observational research method is one that does not interfere with the object of your research. It is effective when used at the beginning of your research to develop hypothesis and to come up with coherent problems to be solved. For example, as a mystery shopper, you can observe consumer behavior when they are shopping for certain products. You can also compare the shopping behavior of different classes of consumers by observing them.
Case studies are popular research methods because they can generate a lot of useful findings when used properly. In this method, you extensively analyze individuals, departments, units and organizations with the aim of finding a dominant theme among the cases. The information derived from these cases is then compared and contrasted to support or negate a hypothesis. For example you can analyze the marketing strategies of two organizations to explain the success or failure of either strategy.
The survey method involves assessing people's perceptions and behavior with regard to a set of things. It is carried out by asking people structured questions which may be closed-ended or open-ended. After choosing a sample population or unit, you can hand out questionnaires, make telephone surveys or interview sample populations face to face. For example a survey can be used to study the effectiveness of your school's customer service.
Explanatory research method is used at the initial stages of research. A business student uses this method to formulate a hypothesis and to gain more information about the object of study. For example, you can read literature related to your area of study and discuss with colleagues and your professors to gain further insight of the problem at hand.
Causal research method is used to determine how certain actions influence business results. For example, by carrying out surveys, observations and case studies you are able to support the best marketing or advertising strategy a company should undertake or even the effects of changing the price, color or packaging of a product.