Here's the paper: http://dash.harvard.edu/bitstream/handle/1/8852185/Kohen.pdf...

The first sentence is: "Tampons are used by up to 70 percent of menstruating women in the United States today, and the average woman may use as many as 16,800 tampons in her lifetime."

Using tampons doesn't rule out using pads, too. If I use a tampon one day, I'm one of that 70% of menstruating women that uses tampons. If I use a pad when I swap out that tampon, I'm now also one of the x% of menstruating women that uses pads.

Realised that the second I pasted the text. It's midnight in Germany ... That's the original link I found: http://askville.amazon.com/AMERICAN-WOMEN-TAMPONS-PADS-PERIO...

And here is another statistic: https://www.ncbi.nlm.nih.gov/pubmed/22980411

They're both not clear though I do think it's fair to say tampons are preferred. Just google for "tampons vs. pads".

how do you use 16800 tampons over a lifetime? that's one a day for 46 years.

Well, if you change your tampon ever 2-3 hours, then you end up using 4-5 a day, which can run up to 30-35 tampons a month, which averages out to a little more than one a day.

That's US only.