respectively. The U.S. is our largest national market, comprising 38% of total revenues in 2014 and 39% of total revenues in both 2013 and 2012. Japan is our second- largest national market, with approximately 9%, 10% and 12% of total revenues in 2014, 2013 and 2012, respectively.

Our policy relating to the supply of pharmaceutical inventory at domestic wholesalers, and in major international markets, is to generally maintain stocking levels under one month on average and to keep monthly levels consistent from year to year based on patterns of utilization. We historically have been able to closely monitor these customer stocking levels by purchasing information from our customers directly or by obtaining other third-party information. We believe our data sources to be directionally reliable but cannot verify their accuracy. Further, as we do not control this third-party data, we cannot be assured of continuing access. Unusual buying patterns and utilization are promptly investigated.

Our gross product revenues are subject to a variety of deductions, that generally are estimated and recorded in the same period that the revenues are recognized, and primarily represent rebates, chargebacks and sales allowances to government agencies, wholesalers/ distributors and managed care organizations with respect to our pharmaceutical products. Those deductions represent estimates of rebates and discounts related to gross sales for the reporting period and, as such, knowledge and judgment of market conditions and practice are required when estimating the impact of these revenue deductions on gross sales for a reporting period. Historically, our adjustments of estimates, to reflect actual results or updated expectations, have not been material to our overall business. On a quarterly basis, our adjustments of estimates to reflect actual results generally have been less than 1% of biopharmaceutical revenues, and have resulted in either a net increase or a net decrease in revenues. Product-specific rebates, however, can have a significant impact on year-over-year individual product growth trends. If any of our ratios, factors, assessments, experiences or judgments are not indicative or accurate predictors of our future experience, our results could be materially affected. The sensitivity of our estimates can vary by program, type of customer and geographic location. However, estimates associated with U.S. Medicare, Medicaid and performance-based contract rebates are most at risk for material adjustment because of the extensive time delay between the recording of the accrual and its ultimate settlement, an interval that can generally range up to one year. Because of this time lag, in any given quarter, our adjustments to actual can incorporate revisions of several prior quarters.

The total deductions from revenues for 2014 increased compared to 2013, primarily as a result of:

• an increase in Medicare rebates due to higher volume of sales in the Medicare patient population;

• an increase in Medicaid and related state program rebates, primarily as a result of a change in our estimates of sales related to these programs;

• an increase in performance-based