Methods are compared, often using a placebo or sham treatment that makes objective measurements possible. There is also a phase process where, for example, pharmaceuticals move from the laboratory, into animals, then into selected individuals, and finally into widespread use. The more you understand about research design, the more comfortable you will be in looking at scientific studies and analyzing where potential problems might arise. Of course, few of us have the background and expertise to determine whether appropriate statistical inferences were made and whether the general study design is robust and well-constructed. Even professionals hire statisticians to do the number crunching.
Validity refers to the extent to which the study measured what it was supposed to.
Reliability refers to whether the measuring device is consistent in measuring whatever it measures. There are many interesting and informative Internet sites that explore all of the above-mentioned processes and concepts. As a good journalist, you shouldn't have any trouble finding them. Also helpful is a working knowledge of the principles of medical genetics, a field that is rapidly becoming a common denominator in many diverse areas. Every disease and condition usually has some sort of organizational umbrella or funding mechanism, and every single one of them will tell you that they are underfunded.