The Twitter (Gnip PowerTrack) sample operator can be very useful if you receive an estimate for a very large number of tweets but do not need the entire population of tweets for your research. The sample operator returns a random subset of the data that match a rule rather than the entire set of tweets, which can substantially lower the cost. The sample percent must be an integer value between 1 and 100. This operator applies to the entire rule and requires any OR’d terms be grouped.
The following is an example that returns a sample of 5% of the data.
(cellphone OR smartphone) sample:5
Please see Twitter's premium operators documentation for more information.