Local Tax Supermajority Requirements

What the evidence says

The clearest empirical pattern in these claims comes from panel data with state and year fixed effects: introducing a two-thirds supermajority requirement is associated with a 0.6 percentage point decrease in the effective tax rate, a decrease of 7 percent relative to the sample average. This estimate holds after controlling for unobserved, time-invariant state attitudes toward taxation, which is the mechanism the source credits for the difference from a simpler cross-sectional approach. A companion instrumental-variables analysis, run with robustness checks across specifications, finds a larger effect on the revenue side: supermajority requirements reduce tax revenues as a percent of personal income by 1.7 to 3.6 percentage points, with the range attributable to which instruments and regional samples are included.

By contrast, a plain ordinary-least-squares regression on the same underlying question finds only a small, negative effect on tax rates that does not reliably differ from zero. The source attributes this weaker result to a form of downward bias: states that already favor lower taxes are more likely to adopt supermajority requirements in the first place, which contaminates a simple cross-sectional comparison and pulls the raw association toward showing less of an effect than the fixed-effects and instrumental-variables designs recover.

Across the fixed-effects and instrumental-variables results, the direction agrees: supermajority requirements are associated with lower tax rates and lower tax revenues. The evidence base here is a single study examined through three different estimation strategies, not three independent studies, so the outcome-level agreement should be read as internal consistency within one research design being pressure-tested, not as independent replication.

No claims below speak to effects on spending levels, service provision, bond issuance, voter turnout, or the frequency with which supermajority thresholds are reached versus missed — those outcomes are absent from the current evidence base.

Where the evidence splits

The OLS estimate and the fixed-effects estimate disagree on whether supermajority requirements have a measurable effect on tax rates. OLS finds a small negative effect that does not reliably differ from zero; fixed effects finds a 0.6 percentage point decrease. The source explains this split directly: OLS is biased downward because states with pre-existing pro-tax preferences are more likely to adopt supermajority requirements, and fixed effects corrects for this by controlling for unobserved state attitudes — though the source also notes fixed effects does not capture state-specific temporal changes in preferences, so the correction is described as partial.

The revenue-reduction estimate itself is not a single number but a range, 1.7 to 3.6 percentage points, produced by the same study depending on specification choices — which instruments are included and which regional sample is used. The source identifies Midwest states as influential outliers driving part of that spread. This is a sensitivity range within one identification strategy rather than a disagreement between separate studies.

Thresholds and dose-response

No threshold established in the current sources.

Open empirical questions

• Do supermajority requirements change spending levels or service provision, as opposed to tax rates and revenues?
• What happens to outcomes when a supermajority vote fails to reach the threshold versus when it succeeds — is there a distinct effect at the margin of passage?
• Do the tax-rate and revenue effects persist, grow, or fade over the years following adoption of a supermajority requirement?
• How does the size of the supermajority threshold itself (for example two-thirds versus a lower supermajority) change the magnitude of the effect?