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get_volatility_index
Get Volatility Index
What it answers
The County Volatility Index, ranked across counties, states or insurers: per 100 members of individual Medicare Advantage plans the September before a plan year, those whose plan ended, who were moved into another plan by their insurer, or whose plan stayed and made a material cut (premium up $10+ a month, in-network MOOP up $500+, comprehensive dental max down $500+ or dropped). Use it for 'most volatile counties in Texas for 2027', 'which insurers' members faced the most change', 'regular PPOs vs HMOs', 'which counties settled since 2023'. For ONE county's full picture (its index every year, by product type, its rank and the plans behind it) use get_county_view with sections=volatility.
ARGS: level (county default, state, parent = CMS parent organization the September before); state (two letters, narrows counties or parents to one state); product (all default, or regular_hmo, regular_ppo, regular_other, dsnp_hmo, dsnp_ppo, csnp_hmo, csnp_ppo, isnp_hmo, isnp_ppo); year (plan year 2016-2027, default 2027); compare_year (default 2023; 'none' to omit); order (most default, or least); min_members (default 250; counties also need 2+ plans to be ranked); limit (default 25, max 200) and offset.
RETURNS value.rows (rank, name, members, plans, index, plan ended / moved / material cut / gains per 100, the compare-year index and the change), value.scope (the same figures for the whole state or nation), value.nation, value.summary (how many entities passed the size rule).
RULES THE TOOL ENFORCES: every year is plans as filed against the prior September's members, what members face, not outcomes; before 2021 only the exit part (plan ended + moved) exists and is never called the index; rates are sums of members, county indexes are never averaged; small counties are counted in totals but never ranked; special-needs plans are their own product types; plans that only followed CMS's MOOP ceiling are their own line, never a cut.
SOURCE: Vlada analysis of the CMS plan crosswalk, Landscape, plan benefit filings and monthly enrollment by plan and county (County Volatility Index v4, Report 2).
Inputs
compare_yearlevellimitmin_membersoffsetorderproductstateyearCall it
From an agent: connect the Vlada MCP once (one click for Claude, ChatGPT, Cursor, VS Code) and ask in plain English; the agent selects get_volatility_index when the question fits. From code: the same tool over REST with an API key. The schema endpoint needs no key.
curl -X POST https://api.vladahealth.com/v1/tools/get_volatility_index \
-H "Authorization: Bearer $VLADA_API_KEY" \
-H "Content-Type: application/json" \
-d '{}'curl https://api.vladahealth.com/v1/tools/get_volatility_index/schema # the JSON schema, no auth # MCP endpoint (Streamable HTTP): https://mcp.vladahealth.com/mcp
What comes back
Typed rows plus provenance on every answer: the public source file, its vintage, the methodology, and a response_hash you can replay. Prove and replay tools turn any number into a re-runnable receipt. A number the data cannot support comes back as “not in the data”, never as zero.
Sources behind it
- medicare_semantic.cvi_plan_county_v4
views: medicare_semantic.cvi_plan_county_v4
Known limits
- Every year is plans as filed against the prior September's members: what members face, not where they go.
- The benefit part is a floor: over-the-counter and Part B giveback cuts are not counted.
- Benefits are scored from 2021; earlier years carry plans ending and members moved only.
As of the 2026-10-26 build of the served surface · machine-readable catalog · the live server may run a different version; the schema endpoint above is authoritative for what is deployed.