Within each field of study, some study designs or types of information are considered to be more reliable sources of evidence than others. For example, in clinical medicine, randomised controlled trials are the gold standard because their study design inherently eliminates bias that would otherwise make the results less reliable (eg because of the well-known placebo effect). Such trials can be well or less well conducted. To write accurately about evidence in a specific discipline, it is important to be familiar with the hierarchy of evidence in your discipline and what defines a well-conducted study or investigation.