When new events are added they are not in chronilogical order. How do I fix this?

Whenever I would add new photos to my library, the new event would be created in chronological order ... oldest to newest. To my knowledge I made no changes in my set-up, but now the newest event is created immediately before the oldest event. In other words it will be listed first not last. How can i change this so that events are listed in order. (At this point I simply drag the event to the proper location.) The only thing that is different now than any previous file is that some files are now in RAW format instead of JPEG. I am using iPhoto '11; version 9.4.3.

Thanks,

Peter