Today, we can measure interplanetary distances far more accurately than the transitmethod allows, though amateurs can still contribute their measurements using an app from Astronomers Without Borders.
The transitmethod for finding planets searches for the small drop in brightness of a star that occurs when a planet passes in front of it and blocks some of its light.
Ian Roxburgh, professor of astronomy at Queen Mary, University of London, said the transitmethod still favoured the detection of big planets, because they blocked out more light from the parent star.