Ferrari's five times world champion told his team's website on Monday that the first half of the season, with five different winners in eight races, had shown how hard it was to make predictions.
"It seems that the pecking order varies from circuit to circuit, with the result depending each time on the track layout," said the German, whose next race is on Sunday at the Nuerburgring circuit near his birthplace.
"I think that trend will continue in the second half of the season. We will continue to win races, but so will McLaren and Williams.
"I think it will be a tough fight for the title, which is likely to go down to the wire. The competition is close and there will be more changes in the order."
Schumacher has won four of the last five races, after making the worst start to a season in his career, and leads McLaren's Kimi Raikkonen by three points.
McLaren, who have yet to bring out their new car, won the first two races of the season while Colombian Juan Pablo Montoya gave Williams a win in Monaco and Italian Giancarlo Fisichella was triumphant in Brazil for Jordan.
Ferrari's Rubens Barrichello won at the Nuerburgring last year and Schumacher expects the team to do well again.
"Our car's main advantage is that it goes well on all the circuits and we are always in the hunt for the win," he said. "And, in the past few races at the Nuerburgring, Ferrari has usually gone very well."
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