The IMA reverted back to a single UK Equity Income sector on 1 July.
This follows a review of the UK Equity Income and UK Equity Income & Growth sectors which was completed in February 2010.
Following the merger, the classification of the UK Equity Income sector has been adjusted. The goal of achieving a yield in excess of 110% of the FTSE All Share is now expressed as an intention, rather than a necessity, the IMA says.
It will also now be measured over a rolling three-year period.Managers will also have to deliver a base level of income every year and a "hard edged" annual test will be applied to ensure that funds are sufficiently income-focused.
The test has been set at a level of 90% of the FTSE All Share yield.
In addition, the IMA will publish the annual yield achieved by each fund to help advisers make comparisons.
Funds are still required to have 80% invested in equities.
Last year following a consultation, the IMA split the UK Equity Income sector into UK Equity Income and UK Equity Income & Growth.
The new Income & Growth sector only required funds to achieve a return greater than 90% of the FTSE All Share Index.
As of 21 June, there were 17 funds in UK Equity Income & Growth, the largest of which was Neil Woodford's £9.2bn Invesco Perpetual High Income fund.
The change was brought about after firms including PSigma and Credit Suisse called on the Association to temporarily change the yield requirement.
In the wake of the financial crisis, managers were concerned about companies cutting dividends.
Ian Trevers, head of distribution at Invesco Perpetual says: "We welcome the recombination of the Equity Income Sector on behalf of the many advisers and clients whose views we have represented to the IMA during the review process."
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