Answer:
Avoid observer and subject bias
Explanation:
Double-blind study is a human clinical trial method where neither the examiner nor the examiner knows what is being used as a variable at any given time. The purpose of the double-blind test is to avoid any conscious or unintentional interference with the results of an experiment and thus to avoid observer or subject bias in the result of the experiment.
Federalism helped unify the states without destroying all of their governing powers. For example, a centralized government allows the states to use the same currency. However, states would still be able to set their own laws as well, for example, whether a death penalty would be used in the state.
Answer:
Surface and Source
Explanation:
Raymond Cattell was able to distinguish between source and surface traits. Surface traits can easily be known, these traits are very obvious and can be effortlessly identified by other people, meanwhile, source traits are less visible to other people and appear to be the basis for several different aspects of behaviour.