The statement you provided breaks down the proportions of participants who administered the highest level of shock, represented as fractions:
a fourth: This means 1/4 or 25% of the participants administered the highest level of shock.
a third: This means 1/3 or approximately 33.33% of the participants administered the highest level of shock.
half: This means 1/2 or 50% of the participants administered the highest level of shock.
two-thirds: This means 2/3 or approximately 66.67% of the participants administered the highest level of shock.
These fractions emphasize the alarming and concerning compliance rates among participants in the study, revealing the disturbing extent to which individuals were willing to follow authority figures' instructions, even if it meant causing harm to another person.