A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level. Indeed, the Google study indicated that "one of our key findings has been the lack of a consistent pattern of higher failure rates for higher temperature drives or for those drives at higher utilization levels.". Hard drives with S.M.A.R.T.-reported average temperatures below had higher failure rates than hard drives with the highest reported average temperature of , failure rates at least twice as high as the optimum S.M.A.R.T.-reported temperature range of to . The correlation between manufacturers, models and the failure rate was relatively strong. Statistics in this matter are kept highly secret by most entities; Google did not relate manufacturers' names with failure rates, though it has been revealed that Google uses Hitachi Deskstar drives in some of its servers.