Before addressing more specific elements related to what comprises a theory, research question or hypothesis, it is useful to state what a theory actually is and how it can be differentiated from a simple idea or concept a scientist or researcher comes up with. A theory is more than simply an idea because the idea itself forms the hypothesis that in turn is used as the context for the experiments, tests, and gathering evidence that will go to prove or disprove the initial hypothesis.
A theory then is the positive benefits of proof and evidence and is the proven outcome of the subject of the hypothesis. In accordance with this definition, in order for a theory to be scientific, it must be have the burden of proof behind it and must have the evidence that was gathered after the original hypothesis supporting it. In other words, to be scientific, a theory must be repeatedly provable in a controlled testing environment over the span of time with little room for doubt at the end of the process.
With the above definition in mind, theories are directly related to evidence and, in fact, could not even exist without ample evidence that can be reproduced by multiple testers. For a theory to be accepted, without tests that prove and give solid evidence to the original hypothesis that forms the basis of the theory, the theory is not scientifically valid and is thus reduced to being still in the stage of a hypothesis. Evidence is therefore the key element to the formulation of a proper theory as without it, there would be no way to prove or disprove a hypothesis. The reliability and validity of a theory hinges on the ability to produce repeatable and quantifiable evidence, as without it, there are no other ways to rationally and scientifically declare a theory valid.
Evaluating a theory is more than simply finding enough evidence to take an idea from the stage of hypothesis to theory, it is a complex and often time-consuming process called the scientific method. What the scientific method does is helps to develop a theory through stages, the first of which is the process of observation. During observation, generalizations are made about the idea in question and a series of limiters and known factors are delineated. An analysis of the observations yields the hypothesis, which will be the subject of rigorous tests (which is the next stage in the process) that set to offer evidence or show a lack thereof about the hypothesis. The results of these tests are recorded and offered for scientific review, often among peers in the same field of study or research and the hypothesis in question is then judged according the same scientific method in many places and contexts, and by many other researchers until it can be universally agreed upon or left in question due to a lack of evidence or evidence that is not repeatable or generally always the case. Again, the most important issue in evaluating a theory is the production of reliable evidence that can be supported by other researchers.
With these general statements about the formulation of a theory and issues related to what theories are and how they are supported apply across several fields of inquiry, they can be easily applied across in the spectrum in psychological research and clinical psychology contexts. Coming up theories is an important part of psychology as researchers and clinicians attempt to make useful generalizations about conditions, factors that influence mental illnesses or imbalances, for instance, or any other subset of psychological research. To be the most productive, psychology requires theories that are supported by many researchers and that can serve as a standard for treatment, further research, and the formulation of better policies, practices, and guidelines in both the psychology research and clinical contexts.