Better way to word this expression.

Again, from something I'm editing for an internship, here is a sentence that I am thinking might sound better if slightly reworded:

This may be the reason why mobile marketing has a five-times higher response rate than direct mail, [rest of the sentence not relevant].

Would it be better to use "five-time"? Neither really sound good to me. I am thinking maybe using five-fold instead. Are there other options? Or which is best?

Thanks again so much for your help!