You can see this for yourself if you sync your phone with your laptop. Go to your phone's backup folder. On this Mac, it's ~/Library/Application Support/MobileSync/Backup/[big random string here]

Once you're in that directory, grep for the file that contains the sqlite database by looking for a text string used only in it: 'grep appLaunchCount *' works. You'll get one result. Pop that baby open with a sqlite editor - I use MesaSQLite, myself, but it doesn't matter which.

In the database's Scalars table, you'll see three columns - key, daysSince1970, and value. For each day in the last couple of weeks, and for each app you've used, there will be the following keys:

-- appActivationCount.com.[app name here]

-- appActiveTime.com.[app name here]

-- appBackgroundActiveTime.com.[app name here]

-- appLaunchCount.com.[app name here]

The values are the number of times the app was launched & activated that day, and how long the app was active in seconds. Not 100% sure on the difference between appActiveTime and appBackgroundActiveTime - perhaps the latter involves the app actively doing something while in the background?

There's a bunch of other data in that file as well, but that's the stuff relating to frequency and length of app usage.