I notice that featured image threads accumulate both submissions and votes at the same time. This means that there's a bias towards submissions that happen earlier in the week. Also, the time at which voting closes is not specified in the question.
That doesn't seem right to me, for three reasons:
- We shouldn't require people to rush to submit in the first days of the week.
- Even if we think this bias is OK, we should disclose clearly what is happening.
- People should be able to know a deadline for their votes (this in particular has been asked for repeatedly in comments to featured image questions).
I'm a scientist, so I like numbers. I went through the last six weeks of featured image threads and wrote down the votes of each image and the number of days prior to the "week of" day (since the voting deadline is never specified, I can't count how far before the deadline it was).
I found no relationship between fraction of total answer votes on the question and submission time (while people can keep voting after a featured image thread closes, I suspect this didn't have a large effect).
However, I then looked at when people submit (sorry for the inappropriately large graph):
The X axis is the number of days before the featured image goes live, and the Y axis is the number of submissions which are that early. For example, the peak is: 12 submissions have been made 7 days before the go-live date.
Bottom line: We already behave as if there are distinct submission and voting periods. Let's be explicit and honest about this.
(By the way, I still believe that there's much bias towards submissions that happen early, but since they all happen early, there's no practical effect.)