I'm trying to find a ratio of how many times the average Japanese
person calls in sick compared to the average American.

Example: In 1999, The average American worker called in sick 4 times
more than the average Japanese worker.

I would prefer a credible study, if any have been done. I don't need
info such as how many vacation days the average person in these two
countries have. Just the ratio.

Good luck. I have tried many different patterns in google with no luck.

Quick anecdote:

A colleague of mine, an American, spent a year working in Japan.  He
woke up one day feeling flu-ish and called in sick.  He was surprised,
later that day, to hear a knock at the door, and there was his
Japanese supervisor, who had come to check up on him...not because the
supervisor thought he might be shirking, but because the Japanese
apparently don't take days off unless they're at death's door.  The
supervisor was afraid my friend, as an American, was hesitant to get
himself to the hospital, where he "obviously" needed to be, since he
was too sick to come to work.

Another anecdote: In my younger years, I once worked as a secretary
for a well-known Japanese company in New York City; at that time, all
the employees I came into contact with were male and Japanese, except
the secretaries, who were female and American. Whenever male collegues
from Japan came to New York on business, it was customary for certain
men in the office to make to spend the night on the town with them.
Every time, the following morning, the guys came with what looked like
truly miserable on-death's-door hangovers. They were so bad that by
going-home time, they still looked hung over! But they *never* called
in sick.

Kriswrite

I've worked in America, and I currently work in Japan.  I call in sick
now just about as often as I did when I worked in America.

I don't think that comparing America and Japan directly will yield
particularly interesting results because Japan needs to be divided
into two distinct subgroups:  Japanese companies and foreign
companies.  Policies and stigmas regarding taking sick days will vary
greatly between the two.  Results will also vary greatly between
departments.  Comparing the results of a sales team where members make
a large portion of their pay through commissions and an I/T department
would be like comparing apples to mikan...