Karlsruhe, Germany - Germany's top court ruled Thursday that a feature of federal election law was unfair and ordered an amendment by 2011, after the next general election.

In a close-run election, the method of calculating each party's seats in the Bundestag parliament can be crucial.

Two citizens took the case to the federal constitutional court, saying that the calculation sometimes had the paradoxical effect of depriving a party of seats as its proportion of votes nationally rises.

Germany uses the mixed member proportional (MMP) system of vote counting. Voters choose a Bundestag member to represent each of 299 districts and cast a "list vote" to fill 299 more seats, proportional to overall party support.

The distortion can arise when a big party wins a greater fraction of the electoral districts than its proportion of all votes.

The current 612-seat parliament would have had only 597 seats, after the death of one member, if it were not for 15 "overhang" seats won by the member method by Chancellor Angela Merkel's Christian Democrats and her coalition partners, the Social Democrats.

The parties have learned to try to win as many overhang seats as possible.

The paradox arises when the discrepancy between member and proportional seats reduces. A party may end up with fewer seats overall because of the way the seats are distributed state by state.

In 2005, Merkel's party urged supporters in one district to leave the proportional part of their ballots blank to prevent this.

Judges in Karlsruhe said this effect contradicted the principle of equality between parties under electoral law, but said there should be no change in the distribution of seats in the current Bundestag. It set a deadline of June 2011 to pass amended electoral legislation.

The calculation method led to "arbitrary results" and these outcomes were by no means rare, the judges said. (dpa)