Mobile app users that opt in to push notifications have a 26 percent higher retention rate after one month and double the retention rate after six months compared to users that don’t, according to Urban Airship.

The company, which provides notification and in-app purchase solutions to mobile app developers, reported the figures today as part of its new Good Push Index. Starting in August 2011, Urban Airship studied apps using its service that had at least 10,000 opens in order to track the engagement and retention of users that opted into its notification service.

The study revealed that six months after the initial download, over 30 percent of users that received push notifications were still using an app. By comparison, less than 20 percent of non-notified users still used the same app after six months. Urban Airship also found that push notifications users were overall far more likely to increase their use of an app over time.

While the Urban Airship stresses the specific settings required to optimize the effect of push notifications will vary from app to app, the company has outlined several best practices for developers in its Pocket Guide to Push. Some of the pointers are obvious — like maintaining brand consistency in push notifications or analyzing push notification results to determine what kinds of messages resonate with users. We’ve highlighted some of the more interesting points below. You can the full study here.

• Allow users to control the flow and timing of push notifications. Apps using push should include an easy to find settings area where users can turn notifications on and off and control when they will (and will not) receive notifications.
• Deliver messages that are relevant to an app’s users first, and to the app’s sales targets second.
• Deliver relevant notifications by letting users choose what kind of notifications they receive from an app. The ESPN ScoreCenter app allows users to customize notifications for specific sports, teams and game events.
• Push users to relevant content, such as landing pages and videos directly related to the text in the notification.
• Use push to improve the user’s current situation, like using location information to push relevant information to users such as daily specials and coupons.