Statistical data on global software development industry / market size

Where can I find statistical data related to the evolution of the global software development market? I’m looking for data related to the evolution of at least one of the following: • the number of software professionals in the world; • global software spending; • global software development companies revenue; • number of software development companies. I need data for at least 20 years. I’ll be using the data for a research I’m conducting in a PhD programme.