Val,
Sometimes being quick is more useful than being completely right. You knew that others would contribute after you, so that your answer wouldn �t be the only one, so it �s a good thing. Prepositions are difficult in every language, so explaining them is never easy.
First of all, we don �t often use the expression "during the past few years". There �s definitely nothing wrong with it, but its meaning is very specific, so it isn �t all that useful. "During" is used to describe something that happens within a specified time period, with an emphasis on "within", when used with a period of time, or "at the same time as" when used with an event.
During the Civil War, women in the US wore hoop skirts. ("During" here means that the fashion happened at the same time as the war, although in this case it wasn �t limited to exactly that time.
During my lecture, two students in the back were looking at their phones.
Please visit me during my office hours. (within my office hours)
During the past few years, I �ve had two periods of unemployment. (within that time period). I can �t say "for the past few years", because I wasn �t unemployed that whole time.
During the past few years, that country has had three revolutions. (within the period)
For the past few years, that country has been very unsettled. (over the whole period)
Bruce
