MTTR is a great starting place for teams just starting out on their Incident Response and Incident Management journey. But if your team has been working on IR for a while, you might need a bit more than MTTR can give you.
Google and others have written about some of the weaknesses of MTTR, and @mandi.walls took a look at where you can get better insights in your PagerDuty account.
PagerDuty Blog: Improving Beyond MTTR with PagerDuty Analytics