A counselor asks observers to rate frequencies of aggressive actions by children in a playgroup. Most of the children are neatly dressed and well-groomed, but a very few are untidy and disheveled. If the observers' ratings were biased because they equate untidiness and aggressive behavior, it would be an example of the ____ effect.

a.

Hawthorne

b.

Multiple treatment

c.

Halo

d.

Placebo