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Reposted by Matt Fiedler

Ryan Hill @ryanreedhill.bsky.social · 11/03/2026

There is great excitement about the potential for AI to reshape science, but so far very little empirical evidence about how that is (or is not??) happening in real time. I'm excited to share a new working paper with Carolyn Stein about the impact of AlphaFold on science ->

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

(Addendum: Another way of looking at this is that the WH envisions a “minimum premium” requirement that goes far beyond just requiring all enrollees to pay a de minimis premium. Either way, the incipient WH proposal is much stingier than meets the eye.)

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

But, before even getting there, it’s important to recognize that what’s been called a WH proposal to extend the enhanced subsidies actually falls well short of a full extension. /end

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

To gauge the proposal’s overall impact, one would also need to consider the proposal’s cuts to the underlying subsidy structure (i.e., the new $5 minimum premium & ending silver loading), the new HSA proposal, and the various regulatory and other changes.

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

While there’s been a lot of attention to the fact that the White House was going to propose not extending the enhanced credits above 700% of the FPL, these changes below 200% of the FPL would be far more consequential, both in coverage and fiscal impact.

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

In 2025, people below 133% of the FPL accounted for about a quarter of enrollment (> 6 million people), and the 133-200% of FPL group accounted for close to two-fifths of enrollment (~9 million people). All told, about 2/3 of Marketplace enrollees have incomes below 200% of FPL.

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

That change would wipe out almost all of the benefit of the enhanced credits for people with incomes below 133% of the FPL and much of the benefit for people in the 133-200% of FPL range (about two-thirds right at 133% of the FPL, falling gradually to zero at 200% of FPL).

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

Press accounts suggest that, under the incipient WH proposal, all of these applicable percentages would go up to at least 2%. (The phrasing here is a little bit unclear, but this seems like the most sensible interpretation of what’s written.) apnews.com/article/trum...

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

What Congress did in the ARP/IRA was lower these applicable percentages (and newly create one for people at or above 400% of the FPL). This is what makes the “enhanced” subsidies “enhanced.” See the enhanced & underlying schedules below.

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

Some background: the generosity of the premium tax credit is controlled by “applicable percentages” set in law, which determine the percentage of income that a subsidy recipient is expected to contribute to a benchmark plan. They vary based on income.

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Matt Fiedler @mattafiedler.bsky.social · 26/11/2025

There’s a feature of the abortive White House ACA subsidy proposal that I think has been underappreciated. Namely, it seems to only partially extend the enhanced subsidies for people with incomes below 200% of the FPL (~$31k for a single person). That’s about 2/3 of enrollees.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Addendum: Ack. This tweet had crucial typo. The 2nd sentence should be "Enrollees who shift from TM to MA when MA grows are likely *cheaper* than the average TM enrollee but *costlier* than the average MA enrollee, so *both* groups likely get more costly as MA grows." bsky.app/profile/matt...

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Ack. This tweet had a crucial typo. The second sentence should read "Enrollees who shift from TM to MA when MA grows are likely *cheaper* than the average TM enrollee but *costlier* than the average MA enrollee, so *both* groups likely get more costly as MA grows."

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

To be clear, the MA payment system’s *existing* accuracy problems may (and, in my view, do) offer a strong rationale for reform. But the dynamics we consider here seem unlikely to do much, if anything, to bolster that case. /end

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

A second is that rising MA penetration is unlikely to change selection patterns in ways that seriously reduce the accuracy of the MA payment system and necessitate reforms that would break the link between MA payments and TM costs.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

If that’s right, it has a couple of implications. One is that TM is likely at little risk of entering a “death spiral” in which higher MA penetration leads to greater favorable selection that induces still further increases in MA penetration, and so on.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Our approach has limitations, including that it cannot address potential confounding from county differences that vary over time. But these results suggest that further growth in MA will have little effect on the degree of favorable selection into the program.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

For example, the results imply that if TM’s market share fell by 50%, then the effect on the TM-MA difference in risk-adjusted costs would lie somewhere between a negligible change and a decline of around 0.6 percentage points.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Details are in the paper, but this figure shows the main results: across a wide range of assumptions about who “switchers” are (reflected in the different values of theta), changes in MA penetration have little effect on the degree of favorable selection into MA.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

The panel data allow us to control for persistent cross-county differences, while the model structure allows us to explicitly account for the fact that stayer-switcher cost differences may not coincide with differences in average costs between TM and MA enrollees.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

To address these issues, we use county-year panel data on MA penetration and stayer-switcher differences to estimate an empirical version of the theoretical model sketched above.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Under this assumption, the model sketched above suggests that stayer-switcher cost differences may shrink as MA grows even if the difference in average costs between TM and MA enrollees is stable or growing. See, in particular, panels A and B below.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

This matters because MA penetration may not affect the two differences in the same way. To see why, suppose we make the (arguably fairly plausible) assumption that TM-to-MA “switchers” correspond to the enrollees on the margin between TM and MA.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

The second issue is more subtle. TM-to-MA “switchers” are likely not representative of MA enrollees as a whole, so the cost difference between stayers and switchers may not measure what we’re actually interested in: the difference in the *average* cost of TM and MA enrollees.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Indeed, it’s notable that *changes* in MA penetration are associated with modest declines in stayer-switcher differences, consistent with the concern that cross-sectional relationships are confounded to some degree.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

The first is the potential for confounding. Counties with higher MA penetration may differ in other ways that affect stayer-switcher differences, masking the true causal relationship between MA penetration and stayer-switcher differences.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

But for a couple of reasons, this may not be a good guide to the causal effect of MA penetration on the degree of favorable selection into MA. There are two main issues.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Prior work has examined the cross-sectional relationship between MA penetration and stayer-switcher differences in risk-adjusted costs, finding little relationship. We replicate that finding:

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

If “switchers” have lower prior year spending than “stayers” (after risk adjustment), that’s indicative of favorable selection into MA. Larger stayer-switcher differences suggest more intense selection.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Thus, we tackle this question empirically. To do so, we first construct a measure of favorable selection at the county-year level. Following prior work, our measure is the difference in the prior-year spending between TM-to-MA “switchers” and TM “stayers.”

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

As illustrated in the figure below, the *gap* between the average cost of MA and TM enrollees can either grow or shrink as MA gets larger, depending on the exact shape of the relationship between beneficiary cost and propensity to enroll in MA vs. TM.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

As a theoretical matter, it’s ambiguous how MA’s growth will affect selection. Enrollees who shift from TM to MA when MA grows are likely costlier than the average TM enrollee but cheaper than the average MA enrollee, so *both* groups likely get more costly as MA grows.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Many observers have asked how selection might change as MA grows—and whether this might necessitate policy changes, especially steps to break the link between MA payments and TM costs. See e.g., www.healthaffairs.org/content/fore... jamanetwork.com/journals/jam... www.medpac.gov/wp-content/u...

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

It’s well-documented that Medicare beneficiaries who choose MA cost less to cover than those who choose TM. Because payments to MA plans are based on local TM costs, this “favorable selection” causes MA plans to be paid more than intended.

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Matt Fiedler @mattafiedler.bsky.social · 10/10/2025

Will Medicare Advantage’s growth change the degree of favorable selection into the program? My new paper w/ Samantha Crow offers an answer: probably not much. www.brookings.edu/articles/wil...

brookings.edu

Will Medicare Advantage's rise strengthen or weaken favorable selection? | Brookings

Samantha Crow and Matthew Fiedler examine the effect of Medicare Advantage penetration on favorable selection.

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Matt Fiedler @mattafiedler.bsky.social · 01/07/2025

What will the Senate bill mean for health coverage? We don’t yet have final CBO estimates, but it’s clear they’ll be pretty similar to the House bill. That puts the U.S. on track for an unprecedented increase in the uninsured rate that will wipe out ~3/4 of post-2013 declines.

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Matt Fiedler @mattafiedler.bsky.social · 28/06/2025

The Senate reconciliation bill, at least in its current form, appears likely to reduce coverage about as much as the House bill. If it becomes law, that would mean reversing most of recent years' insurance coverage gains: bsky.app/profile/matt...

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Reposted by Matt Fiedler

Adrianna McIntyre @adrianna.bsky.social · 26/06/2025

New-to-me nugget on work requirements implementation in here: Pinging Equifax's The Work Number — which states are likely to rely on to get recent-enough employment data — "sometimes costs over $20 per person per query"

donmoynihan.substack.com

How Medicaid Work Requirements Betray Work and Waste Money

I Oversaw Work Requirements in Michigan - Here is What I Told Congress

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Matt Fiedler @mattafiedler.bsky.social · 25/06/2025

Full piece is here: www.healthaffairs.org/content/fore...

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Matt Fiedler @mattafiedler.bsky.social · 25/06/2025

Clever new piece from Kennah Watts and Jack Hoadley takes a first look at how decisions under the No Surprises Act arbitration process vary across arbitrators. Lots of interesting findings here, including that provider win rates vary a lot by arbitrator.

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Matt Fiedler @mattafiedler.bsky.social · 16/06/2025

From a first look at the Senate drafts, the cuts to Medicaid & the Marketplaces are similar to the House’s, maybe even a bit deeper on net. Upshot: these drafts, like the House bill, would put the US on course for an unprecedented rise in the uninsured rate. bsky.app/profile/matt...

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Reposted by Matt Fiedler

Matt Fiedler @mattafiedler.bsky.social · 10/06/2025

My new piece @healthaffairs.bsky.social Forefront finds that if the House bill becomes law and enhanced premium tax credits expire on schedule, the US will see an unprecedented increase in the uninsured rate, wiping out about ~3/4 of the post-2013 decline.

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Matt Fiedler @mattafiedler.bsky.social · 10/06/2025

Read the full piece here: www.healthaffairs.org/content/fore...

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Matt Fiedler @mattafiedler.bsky.social · 10/06/2025

If lawmakers want to change the House bill to avoid this, they’ll have to change the provisions with big coverage impacts. Notably, the bill's provider tax changes, which seem to be attracting the most ire from Senators so far, are a fairly small part of the overall picture.

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Matt Fiedler @mattafiedler.bsky.social · 10/06/2025

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Reposted by Matt Fiedler

Jacob Wallace @jacobwswallace.bsky.social · 02/06/2025

Ok folks, we know work requirements reduce benefits without increasing work (cc: @chloeneast.bsky.social) But who loses benefits and what happens if work requirements are reversed? New evidence from linked SNAP-Medicaid data and a natural experiment in CT tell a concerning story... Thread below 👇

tobin.yale.edu

SNAP work requirements have biggest effect on those least able to work

Most people pushed out of SNAP in Connecticut didn’t find their way back in, even when work requirements were later reversed.

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Matt Fiedler @mattafiedler.bsky.social · 27/05/2025

Read the full paper here: www.nber.org/papers/w33856

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Matt Fiedler @mattafiedler.bsky.social · 27/05/2025

The authors then show that fall birthdays are, correspondingly, least likely to have a doctor’s office or emergency department visit for flu (green line/dots), indicating that higher vaccination rates do indeed translate into greater protection against flu.

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