Final answer:
The researchers assumed that the methods of measuring personality dimensions were both valid and reliable, meaning they consistently produce accurate results that truly measure the personality traits intended.
Step-by-step explanation:
The researchers assumed that the methods of measuring personality dimensions were psychometrically valid and reliable. When researchers use methods to measure aspects of personality, they strive to ensure that these methods consistently produce the same results under the same conditions (reliability) and accurately reflect the actual trait or dimension being measured (validity). By assuming the methods to measure personality dimensions are valid, researchers believe that these instruments or tools accurately tap into the traits or dimensions they're designed to measure. In terms of reliability, researchers expect that the methods will yield the same results across different instances or that different observers will agree on the outcomes they are seeing.
Therefore, the assumption the researchers made about the methods of measuring personality dimensions is that these methods were indeed capable of consistently and accurately capturing the individual differences in personality traits that they intended to measure. Consequently, the correct answer to the question of what the researchers assumed about the methods of measuring personality dimensions is that: 3) The methods of measuring personality dimensions were valid and reliable.