It’s important to use valid and reliable test so that an opinion could be supported with reliable evidence. Test help to evaluate the patient and aid in formulating a course of action (Salkind, 2013). Some of the reasons why informal opinion is not an appropriate measure of behavior are some behaviors can be closely observed and precise than others. It is easier to measure one’s ability. But it is harder to understand how the outcome was reach. It is recommended that the formal method be used because of its Reliability, accuracy, and like stated, more time and work, leads to a better outcome (Salkind, 2013). Salkind (2013) also states that “our understanding of behavior is only as good as the tools we use to measure it". For this student, the statement means that having a better interpretation into our research of behavior requires the use of formal tests and measurements, and helps to ensure that an accurate outcome will be the result. This can affect psychotherapy or consultation in any psychology specialization by helping the practitioner to know what tests of measurement are needed to ensure a successful interpretation. Reference
Salkind, N. (2013). Why Measurement? An Introduction. In Tests & Measurements for People Who Think They Hate Tests & Measurements(2nd ed., p. 13). Thousand Oaks, California: SAGE Publications