Predict how the preference for thin ideal in women might change overtime. what are some factors that might cause preference to strengthen and weaken

As time changes, so do people's preferences. Pop culture has a large influence on this. Many people look to famous people and aspire to be them/look like them. For example, when Marilyn Monroe was alive, she became a sex symbol. This made guys (and girls) realize that you didn't have to be rail thin to be attractive. To be honest, everyone has different things they look for in people. Certain things just become popularized.

is there a year set? the question is incomplete

answer; preconventional;