income tax purposes, decreases in the rate of household formations, or other factors. Changes in housing values and unemployment levels are inherently difficult to forecast given the uncertainty in the current market environment, including uncertainty about the effect of actions the federal government has taken and may take with respect to tax policies, mortgage finance programs and policies, and housing finance reform.
The mix of business we write affects our Minimum Required Assets under the PMIERs, our premium yields and the likelihood of losses occurring.
The Minimum Required Assets under the PMIERs are, in part, a function of the direct risk-in-force and the risk profile of the loans we insure, considering loan-to-value ratio, credit score, vintage, HARP status and delinquency status; and whether the loans were insured under lender-paid mortgage insurance policies or other policies that are not subject to automatic termination consistent with the Homeowners Protection Act requirements for borrower paid mortgage insurance. Therefore, if our direct risk-in-force increases through increases in new insurance written, or if our mix of business changes to include loans with higher loan-to-value ratios or lower FICO scores, for example, or if we insure a higher percentage of loans under lender-paid mortgage insurance policies, all other things equal, we will be required to hold more Available Assets in order to maintain GSE eligibility.
The minimum capital required by the risk-based capital framework contained in the exposure draft released by the NAIC in May 2016 would be, in part, a function of certain loan and economic factors, including property location, loan-to-value ratio and credit score; general underwriting quality in the market at the time of loan origination; the age of the loan; and the premium rate we charge. Depending on the provisions of the capital requirements when they are released in final form and become effective, our mix of business may affect the minimum capital we are required to hold under the new framework.
Beginning in 2014, we have increased the percentage of our business from lender-paid single premium policies. Depending on the actual life of a single premium policy and its premium rate relative to that of a monthly premium policy, a single premium policy may generate more or less premium than a monthly premium policy over its life.
We have in place quota share reinsurance transactions with a group of unaffiliated reinsurers that cover most of our insurance written from 2013 through 2017, and a portion of our insurance written prior to 2013. Although the transactions reduce our premiums, they have a lesser impact on our overall results, as losses ceded under the transactions reduce our losses incurred and the ceding
commissions we receive reduce our underwriting expenses. The net cost of reinsurance, with respect to a covered loan, is 6% (but can be lower if losses are materially higher than we expect). This cost is derived by dividing the reduction in our pre-tax net income from such loan with reinsurance by our direct (that is, without reinsurance) premiums from such loan. Although the net cost of the reinsurance is generally constant at 6%, the effect of the reinsurance on the various components of pre-tax income will vary from period to period, depending on the level of ceded losses.
In addition to the effect of reinsurance on our premiums, we expect a modest decline in our premium yield resulting from the premium rates themselves: the books we wrote before 2009, which have a higher average premium rate than subsequent books, are expected to continue to decline as a percentage of the insurance in force; and the average premium rate on these books is also expected to decline as the premium rates reset to lower levels at the time the loans reach the ten-year anniversary of their initial coverage date. However, for loans that have utilized HARP, the initial ten-year period was reset to begin as of the date of the HARP transaction. As of September 30, 2017, approximately 3% and 1% of our total primary insurance in force was written in 2007 and 2008, respectively, has not been refinanced under HARP and is subject to a reset after ten years.
The circumstances in which we are entitled to rescind coverage have narrowed for insurance we have written in recent years. During the second quarter of 2012, we began writing a portion of our new insurance under an endorsement to our then existing master policy (the “Gold Cert Endorsement”), which limited our ability to rescind coverage compared to that master policy. To comply with requirements of the GSEs, we introduced our current master policy in 2014. Our rescission rights under our current master policy are comparable to those under our previous master policy, as modified by the Gold Cert Endorsement, but may be further narrowed if the GSEs permit modifications to them. Our current master policy is filed as Exhibit 99.19 to our quarterly report on Form 10-Q for the quarter ended September 30, 2014 (filed with the SEC on November 7, 2014). All of our primary new insurance on loans with mortgage insurance application dates on or after October 1, 2014, was written under our current master policy. As of September 30, 2017, approximately 71% of our flow, primary insurance in force was written under our Gold Cert Endorsement or our current master policy.
From time to time, in response to market conditions, we change the types of loans that we insure and the requirements under which we insure them. We also change our underwriting guidelines, in part through