A computer implemented method of analysing event data associated with an application under test executed, at a user device of a user, the test having a plurality of test options associated therewith, the method comprising: providing a database storing a data structure comprising at least one user identifier associated with the user and event data associated with the user identifier (340a, 340b, 340c, 340d) wherein said stored event data was generated from executing at said user device (100, 100a,100b,100c) said application which has been modified using one option ( 450, 460, 470, 480) of said plurality of test options; receiving a request to analyse a test associated with the application under test; in response to said request to analyse a test performing the steps of: retrieving a test identifier associated with the application under test; retrieving from the data structure a user identifier and application event data associated with said user identifier; concatenating the user identifier with the test identifier to form a per-user-per-test identifier; generating a hash of the per-user-per-test identifier; processing the hash to generate an index value, comparing said index value with a distribution of numbers divided into multiple ranges to determine in which range the index value falls, each range being associated with a test option, determining a test option (450, 460, 470, 480) based on the range into which the index value falls, associating the determined test option with the application event data for analysis, and analysing, based on the determined test option, the event data associated with the test option ( 450. 460, 470, 480). providing a database storing a data structure comprising at least one user identifier associated with the user and event data associated with the user identifier (340a, 340b, 340c, 340d) wherein said stored event data was generated from executing at said user device (100, 100a,100b,100c) said application which has been modified using one option ( 450, 460, 470, 480) of said plurality of test options; receiving a request to analyse a test associated with the application under test; in response to said request to analyse a test performing the steps of: retrieving a test identifier associated with the application under test; retrieving from the data structure a user identifier and application event data associated with said user identifier; concatenating the user identifier with the test identifier to form a per-user-per-test identifier; generating a hash of the per-user-per-test identifier; processing the hash to generate an index value, comparing said index value with a distribution of numbers divided into multiple ranges to determine in which range the index value falls, each range being associated with a test option, determining a test option (450, 460, 470, 480) based on the range into which the index value falls, associating the determined test option with the application event data for analysis, and analysing, based on the determined test option, the event data associated with the test option ( 450. 460, 470, 480). retrieving a test identifier associated with the application under test; retrieving from the data structure a user identifier and application event data associated with said user identifier; concatenating the user identifier with the test identifier to form a per-user-per-test identifier; generating a hash of the per-user-per-test identifier; processing the hash to generate an index value, comparing said index value with a distribution of numbers divided into multiple ranges to determine in which range the index value falls, each range being associated with a test option, determining a test option (450, 460, 470, 480) based on the range into which the index value falls, associating the determined test option with the application event data for analysis, and analysing, based on the determined test option, the event data associated with the test option ( 450. 460, 470, 480).