Answer to Question 1
Main effects give an indication as to whether groups differ from one another in a general sense. That is, does an IV have an effect on the DV regardless of the level of any other IVs? A main effect looks at a single variable, ignoring all other variables.
An interaction gives an indication as to whether the pattern of results is complex, so that we can't understand the effect of one IV unless we know something about how it is paired with another IV. Interactions give us pictures of the why we might need to consider two variables in combination rather than separately.
Answer to Question 2
During the war, the Nazis engaged in atrocious research, forcing people to participate, ignoring all considerations of respect and dignity. After the war, countries sought to pass rules that would provide for the safety of future research participants.
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