Welcome to The S-Curve
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The name of the blog, the S-Curve, is a reflection of our logo and the central feature of our prepayment model. S-curves are seen in nature in many phenomenon, from population growth to prepayment and default models. Our first S-curve, in the early 1990s, used the arctangent function, then piece-wise linear functions, and evolved over time to be more complex and vary by FICO, loan size and LTV. This evolution encapsulates both the timeless nature of fundamental relationships and constant innovation to describe them better over time.
We hope you find the information useful and we look forward to your feedback.
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Mortgage Origination in a Post-COVID-19 WorldThoughtsIn this blog post, we used the recently updated Mortgage Market Statistical Annual to examine the dynamics of residential loan origination by state and by market segments and highlight important trends.
From mid-2020 until April 2022, the Fed Funds rate was zero and fixed rate mortgage rates were historically low at about 3% (see Figure 1). Thereafter, the Fed began raising the Fed Funds rate to 5% today and fixed rate mortgage rates have doubled. Mortgage payments became unaffordable to many potential buyers and the mortgage origination volume dropped drastically across market segments and states by 80%. Predictably, the refinance market disappeared. Figure 2 shows that the origination volume for different mortgage products decreased drastically from Q1 2021 to 2023.

Figure 1. 30-Year Mortgage Rate, Fed Funds Effective Rate and PCE Price Index

Figure 2. Origination Volume by Market Composition (Dollars in Billions)
Homeowners with low-rate mortgages have a strong financial incentive not to sell when facing the prospect of buying a new house with a mortgage rate twice as high (lock-in effect). These homeowners on the sidelines reduce both the supply and demand for housing. The countervailing impacts on price make the ultimate effect unclear; prices could rise or fall, but the changes are likely to moderate.
Figure 3 shows two things; (1) the housing price spike during the pandemic when rates were so low and the predicted recent collapse when rates rose and (2) turning points in housing prices lead to turning points in new construction rates weighted by population.

Figure 3. Housing Units Under Construction vs HPI
Looking at the States
Across the 50 states, plus Washington D.C. and Puerto Rico, origination dropped 48% from 2021 to 2022. For some background, YoY changes for the past few months have been positive, with 2019 to 2020 year-over-year (YoY) showing a 78% increase. We have to go back to 2016 to 2017 to see a negative 10% YoY drop and 2017 to 2018 a negative 9% drop. Among the most populous states, California suffered the largest drop YoY, declining by a whopping 60%. Some other states with a big YoY drop in origination include Maryland, 55%, Virginia, 54% and Massachusetts, 53%. On the other end, Texas and Florida had the smallest YoY losses at around 33%.

Figure 4 Originations by State
The situation in California, the most expensive state with the most expensive housing market was obvious; the escalating rate hikes priced many potential buyers out of the housing market in a state already hurt by the high income and property taxes.
The situations in Florida and Texas were drastically different. As low tax states, they represented good buying options even in a severe market turn and suffered the least drops.
Naturally, people are motivated to move to more tax-friendly states such as Florida when they retire. As the global pandemic hit and changed how people live and work, it further amplified that migration trend. Workers who once needed to live in states with hot employment markets like California’s tech hub can now work remotely and leave for other lower-cost states.
From Refinance to Purchase
The ten consecutive Fed rate hikes eliminated the refinance boom and deterred existing borrowers from moving, a combination leading to the plunge of origination. The refinance share has fallen from 71% in Q1 2021 to 16% in Q4 2022. On the turnover side, purchasing activities are still ongoing amidst the high rate environment. Purchase volume is not as drastically changed but still has fallen 13% from 2021. Figure 3 still shows a very steady volume of purchase originations over the past two years, despite its obvious decline over the past months. The decrease of the purchase volume can be attributed to the “lock in effect.”[1] The lock in effect is visible for discount mortgages as it deters potential sellers from giving up their current low-rate loan and finance next property with a more expensive one even if they have plans to relocate.

Figure 5. Purchase vs Refi Origination Volume (Dollars in Billions)
Looking Forward
We will continue to monitor changes in origination trends and their connection with affordability and home prices in our borrower behavior and home price modeling. For additional insight, read AD&Co’s HPI Outlook Update by Alex Levin.[2]
[1] Baker, Joni, and Daniel Swanson. “How to Use AD&Co’s Deep Discount and Super Premium S-Curve Tuning.” Quantitative Perspectives (May 2023).
[2] Levin, Alex. “AD&Co’S HPI Outlook Update: Flat, But Multidirectional.” The Pipeline, no. 182 (June 2023).
The S-Curve Archives
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ThoughtsRecently, aggregators have crossed market borders by issuing residential mortgage-backed securities (RMBS) backed by owner-occupied (OO), GSE-eligible conforming loans. Additionally, conforming mortgage loans have drawn investment interest from insurance companies fronted by aggregators and evaluated by third-party firms. These developments constitute historically rare disintermediations of the nearly monopsonist purchases of conforming loans by the GSEs.
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PodcastJoin Rob Landauer in a conversation with Abe Martin as they discuss his recent Pipeline article, "Modeling the Balance Behavior of HELOC Borrowers." In this episode, they highlight key points from the article as he shares insights into the draw component of HELOCs and provide an update on the beta rele
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News
We’re excited to announce a major addition to the Andrew Davidson & Co., Inc. (AD&Co) team. Industry leaders Kelli Sayres and Gene Park, known for building and scaling leading fixed-income analytics platforms, have joined AD&Co’s Business Development team.
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ThoughtsBuilding on our earlier research on expanded consumer attributes, AD&Co continues to explore how credit data contributes to modeling delinquency and prepayment risk, which are key drivers of mortgage servicing rights cash flows and valuation.
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EventsAndrew Davidson recently joined NFM Lending’s Greg Sher on the One On One podcast to discuss our recent white paper, “The Impact of Moving Away From the Tri-Merge Standard.”
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EventsAD&Co recently sponsored and attended SFVegas 2026 and Optimal Blue Summit 2026. This post shares the AD&Co team's unique perspectives and key takeaways from attending both conferences.
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NewsAD&Co US Mortgage High Yield Indices
The Federal Reserve Economic Data (FRED) portal, housed by the Federal Reserve Bank of St. Louis, has been publishing AD&Co’s CRT indices since 2019. These series posted under the overall name of “US Mortgage High-Yield” include total return rates and credit and option-adjusted spreads (crOAS) – a projected return’s spread over Treasury (in the past, Libor). These series are available going back to 2014-end and tiered by CRT initial supports.
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ThoughtsIn July 2025, the US Federal Housing Finance Agency (FHFA) announced that the government-sponsored entities (the Enterprises or GSEs), Fannie Mae and Freddie Mac, would permit lenders to choose between Classic FICO and VantageScore 4.0 credit score models for loans sold to the GSEs. FHFA also stated in a social media post that the tri-merge standard would be maintained for mortgage underwriting. Nevertheless, some mortgage industry stakeholders recommend moving away from the tri-merge standard for GSE mortgages in favor of a single or bi-merge report standard.
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News
As housing faces more climate threats that result in more losses, the insurance program that it sits on is teetering on the brink of collapse. Yet, the home insurance market has three distinct stakeholders that have competing priorities, and today, there is no motivation for a collaborative solution.
Understanding how to strengthen and protect the current structure requires looking at the cost burdens along with the risk for each of those parties.
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ThoughtsThere has been a flurry of activity in the mortgage markets since the 2018 passage of the Economic Growth, Regulatory Relief, and Consumer Protection Act. This act requires the Federal Housing Finance Agency (FHFA, now known as US Federal Housing) to validate and modernize the credit score models used in the housing finance system. It should be noted that so far, the discourse has been around mortgages sold to the Enterprises (Fannie Mae and Freddie Mac). Ginnie Mae has not provided any guidance on their plans to start using new credit score models.