The earthquake also provided opportunities for researchers to retrofit data in order to model future earthquake predictions. Using data from the Intermagnet Lanzhou geomagnetic observatory, geologists Lazo Pekevski from the Ss. Cyril and Methodius University of Skopje in Macedonia and Strachimir Mavrodiev from the Bulgarian Academy of Sciences attempted to establish a "time prediction method" through collecting statistics on geomagnetism with tidal gravitational potential. Using this method, they were said to have predicted the time of the 2008 Sichuan earthquake with an accuracy of ±1 day. The same study, however, acknowledges the limitation of earthquake prediction models, and does not mention that the location of the quake could be accurately predicted.
What did they collect to use in this method? (If the question is unanswerable, say "unanswerable")
statistics