Here is a fictitious example:
Say your review of the literature shows that we know that smiling causes happiness. It also shows that there is disagreement among researchers and theorists in these areas:
1. on how smiling causes happiness;
2. under what conditions and for what type of people smiling causes happiness; and,
3. what else causes happiness
Your research can contribute to theory on the relationship between smiling and happiness by addressing a) or b). Addressing c) is a completely different matter. c) involves identifying constructs that also cause happiness. You would be unlikely to choose this option, because it is not directly related to the smiling/happiness relationship. It involves you in the huge project of developing a general theory of happiness, which is too ambitious for a dissertation study. If, however, your literature review uncovers a theory of happiness that predicts that smiling causes happiness but no one has done a controlled study to see if it in fact does, then you could conduct a study to see if smiling causes happiness that would contribute to theory.
It is important to understand that a study that looks to see if one variable causes an effect on another does not necessarily contribute to theory. For example, simply looking to see if a treatment works (causes an effect, an improvement, is more effective than a placebo) does not contribute to theory, unless you are specifically testing an untested cause and effect relationship claim made in a theory, as in the happiness theory example. For example, if a theory claims that based on what is known about how Y develops in childhood, treatment or intervention X should produce more Y, you are testing a theory and so contributing to it by providing empirical evidence for or against a theory claim. Without the context of a theory that gives a reason why X causes Y, you are doing an applied study, which is not acceptable for a PhD dissertation.
Back to studying the smiling/happiness relationship. Here is how your study could add to our understanding of the relationship.
Your study could:
1. Address phenomena that mediate the smiling/happiness relationship. Our knowledge of human biology tells us smiling cannot directly cause happiness. Smiling must be the beginning of a causal chain of events ending with happiness. Your literature review would identify plausible links, and your study would examine if they are in fact present when people smile and report feeling happy. Your study would contribute to theory on how smiling causes happiness.
2. Address constructs that moderate the smiling/happiness relationship. Your literature review would show you that smiling only leads to happiness under certain conditions (e.g., when people are in a calm mood and not severely depressed). Your review of the literature would suggest plausible candidates for the conditions under which the relationship holds. Your study would contribute to theory on how smiling causes happiness by telling us something about the conditions under which the smiling/happiness relationship holds.
[Note: Smiling and happiness are phenomena in the world. They are also constructs in theories that researchers must operationalize in order to measure. Once operationalized, we call a construct a variable. Variables usually have a number associated with them. Constructs do not. It makes sense to speak of having an IQ of 100 as measured by a Weschler test, but no sense to speak of having an intelligence of 100.]
Then:
Examine the literature in your topic area and identify five articles published within the past five years that investigate mediating, moderating, or independent variables in an attempt to contribute to theory in the topic area. Write a paper in which for each article, you:
1. Describes the theory the researchers explore. What are the key constructs in the theory? How are they related? Identify which ones are cause, effect, mediating, or moderating constructs. How are the constructs operationalized?
2. Briefly describe the study, including the number of participants and research methods.
3. Briefly describe the statistical analyses used
4. Briefly described the findings and how the researchers interpreted them and their contribution to theory.
Using some or all of the five articles, argue for a gap in the knowledge in the topic area and briefly describe a study involving mediator and or moderator variables that can contribute to theory.
Length: 5-7 pages (app. 350 words per page)