Which of the following BEST describes the condition(s) essential to the "wisdom of crowds" effect?

A) Diversity of opinion
B) Independence of thought
C) Confidence
D) Diversity of opinion and independence

The "wisdom of crowds" effect is best achieved when there is a diversity of opinion and independence of thought among the individuals in the crowd. This ensures that the collective decision or estimate is more likely to be accurate, as it incorporates a wide range of perspectives and minimizes the risk of groupthink or the influence of dominant individuals.