Insights / Discrepancy between Accepted Permissions and Installs

I have a technical question regarding FB Insights:

I've created a开发者_运维问答n app that request an email permission by default (a must), meaning all people who installed the app must have accepted the email permission.

I see a discrepancy between:

1. Permissions --> # of Dialogs Accepted.
2. Active Users --> # of New Installs.
3. Daily New Users --> Total Installs --> Subtracting the # of installs at the [end time] minus # of installs at the [start time], even when testing one day only.

Could you tell what is the difference between the 3?