Free or 99 Cents?

I have a brief question for you. If you were to sell your first novel of a series at a reduced price, would you set the price as permanently free or 99 cents?

Recently, I saw someone do an experiment to see which method creates more income and sales of later books in the series. Surprisingly, he did better with the price set at 99 cents. His thoughts were that people are more likely to read a book they paid for than a book they got for free. And this investment in the 99 cent book leads to a greater commitment, not only to the one book, but also to the second book. He saw a greater profit and higher sales.

This is only one case. What do you think?