Popular Categories

We classified the notifications into categories based on the subject field, which was recorded in the notification logs. We plotted the number of messages sent for each notification category in Figure 1, and the number of users who received the notification message for each category in Figure 2.

  

Figure 1: The total number of notifications sent for each category.

  

Figure 2: The total number of users who received notifications for each category.

As Figure 1 shows, email, weather, news, stock quotes, sports, and horoscopes are the most popular categories in terms of the total number of notification messages. In comparison, weather, email, horoscopes, news, and stock quotes are the most popular categories in terms of the total number of users (see Figure 2). As we had expected, email alerts were very popular. On the other hand, we had not expected weather-related notifications to be so popular. Intuitively, one might have expected stock quotes and news to be more popular, especially since users have to explicitly register for different notification types (including weather), i.e., notifications are not being sent due to some default setting on the user-signup page. Another surprise was the low popularity of calendar alerts. For calendar alerts, it is possible that subscribers use handheld devices that are not connected to the wireless Internet, for example, PDAs with pre-installed software to handle scheduled meetings, anniversaries, etc.

  

Figure 3: Change of user interest between weekday and weekends

Next we analyzed how user interest changed during the course of a week. Figure 3 shows a comparison between the amount of notification data sent on a weekday versus a day on the weekend. As one would expect, there is a significant difference between the number of stock quote alerts sent during the weekday compared to those sent on the weekend. Similarly, there are fewer mail alerts on weekends; this is probably due to lower levels of work activity that occur on weekends relative to weekdays, resulting in fewer triggering events. For other categories (e.g., sports, weather, horoscopes), the number of notification messages does not vary significantly over weekends and weekdays. We attribute these patterns to the fact that not many users personalize all aspects of their notification portfolio in a very fine-grained manner (for event types such as weather, the web site allows users to select the frequency and the time of delivery).