A social networking system receives messages from users that include hashtags. The social networking system may use a natural language model to identify terms in the hashtag corresponding to words or phrases of the hashtag. The words or phrases may be used to modify a string of the hashtag. The social networking system may also generate computer models to determine likely membership of a message with various hashtags. Prior to generating the computer models, the social networking system may filter certain hashtags from eligibility for computer modeling, particularly hashtags that are not frequently used or that more typically appear as normal text in a message instead of as a hashtag. The social networking system may also calibrate the computer model outputs by comparing a test message output with outputs of a calibration group that includes positive and negative examples with respect to the computer model output.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method comprising: accessing a trained computer model that predicts membership in a group; receiving a set of calibration data items, each calibration data item having a known membership in the group; applying a computer model to each of the calibration data items, the output of the computer model generating a calibration value for each of the calibration data items that represents a predicted probability of membership in the group; receiving a test data item having an unknown membership in the group; applying the computer model to the received test data item to generate a test output value; selecting a subset of the calibration data items that have a calibration value within a range of the test output value; and adjusting the test output value based on the membership in the group of the selected subset of calibration data items. 2. The method of claim 1, wherein membership in a group comprises association with a hashtag of a message. 3. The method of claim 1, wherein the range for selecting the subset of the calibration data items comprises selecting a number of data items with calibration values above and below the test value. 4. The method of claim 1, wherein the range for selecting a portion of the calibration data items comprises a numerical range, and the subset of data items are within the numerical range of the test data item. 5. The method of claim 1, wherein the improved prediction is a percentage value of the selected portion of calibration data items that are members of the group. 6. The method of claim 1, further comprising associating the test data item to the group when the improved prediction is above a threshold. 7. The method of claim 6, wherein the test data item is a message in a social networking system, and the group is a topic in the social networking system. 8. A method comprising: accessing a trained computer model that predicts membership in a group; receiving a set of calibration data items, each calibration data item having a known membership in the group; applying a computer model to each of the calibration data items, the output of the computer model generating a calibration value for each of the calibration data items that represents a predicted probability of membership in the group; generating a calibration mapping for a range of output values of the computer model based on a comparison of the generated calibration values and the membership in the group; receiving a test data item having an unknown membership in the group; applying the computer model to the received test data item to generate a test output value; and adjusting the test output value based on the calibration mapping. 9. The method of claim 8, wherein membership in a group comprises association with a hashtag of a message. 10. The method of claim 8, wherein generating the calibration mapping for the range of output values of the computer model comprises: identifying a plurality of mapping values within the range of output values, and for each mapping value: selecting a subset of the calibration data items that have a calibration value within a range of the mapping value, and determining a mapping for the mapping value based on the membership in the group of the selected subset of the calibration data items. 11. The method of claim 10, wherein the range for selecting a portion of the calibration data items comprises a numerical range, and the subset of data items are within the numerical range of the test data item. 12. The method of claim 10, wherein the mapping for the mapping value is a percentage value of the selected subset of calibration data items that are members of the group. 13. The method of claim 8, further comprising associating the test data item to the group when the improved prediction is above a threshold. 14. The method of claim 13, wherein the test data item is a message in a social networking system, and the group is a topic in the social networking system.