This interactive chart shows how concentrated GP referrals are across different providers, including Independent Sector Treatment Centres (ISTCs).

It uses the Herfindahl-Hirschman Index of Concentration (HHI), which analyses the market shares for the 50 largest providers by referral volume (number of patients) for the given GP practice, to arrive at a number between 0 (complete diversity) and 1 (total monopoly).

The chart shows a reduction over time in the level of concentration: in other words, an increasing propensity to refer to a more diverse portfolio of providers.

The amount of concentration decreases when private as well as NHS providers are included, particularly after 2007/8, suggesting that the introduction of ISTCs may have played a role in driving this diversity.

This chart is taken from the report: Choosing the place of care: the effect of patient choice on treatment location in England, 2003 to 2011 (Nuffield Trust, November 2012).

This report forms part of a three-year joint research programme between the Institute for Fiscal Studies and the Nuffield Trust: Understanding competition and choice in the NHS.This will establish a long-term expertise in the use of competition and market mechanisms in health care in England and internationally.

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