Switzerland has a stable, prosperous and high-tech economy and enjoys great wealth, being ranked as the wealthiest country in the world per capita in multiple rankings. The country has been ranked as one of the least corrupt countries in the world, while its banking sector has been rated as "one of the most corrupt in the world". It has the world's twentieth largest economy by nominal GDP and the thirty-eighth largest by purchasing power parity. It is the seventeenth largest exporter. Zürich and Geneva are regarded as global cities, ranked as Alpha and Beta respectively. Basel is the capital of the pharmaceutical industry in Switzerland. With its world-class companies, Novartis and Roche, and many other players, it is also one of the world's most important centres for the life sciences industry.