Adulthood covers the four decades of life between ages and

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.

i heard they are taking it off i hope this isn't true but otherwise if it doesn't get taken off it will probably be in early december or early january of 2018-2019

answer; participant observation method;

answer; a biased sample;