It doubled, or in this case, increased by 1.6%. That's nice, but how can you know that a 1.6% increase is a direct result of these tweaks, instead of just natural ups and downs in email response? Maybe 1.6% of recipients were having an unnaturally good day and decided to click that month? That's only 1 in 98 people after all. If it had been 10% or something like that then that's an obvious difference, but 1.6%?