How frequently do people change passwords
Study: Consumer Survey: Password Habits
Date: September 2012
Frequency of password changes by percentage of respondents:
Some of these passwords are likely subject to a maximum age enforced by technical controls in the application or system. So change frequency may not be a voluntary choice by the user.
Also keep in mind that this answer may represent several different passwords being changed in a given time period, as opposed to how frequently a single password is changed.