It's called science. You can most certainly have several variables in a well planned study. You think when companies do studies there are no other variables to consider? As long as the population is sufficient and they used sound statistical analysis you can have several variables in a single study and still determine effectiveness. You are trying to make very normal scientifically valid study look like it's not, and we haven't even seen the results yet! Which is clearly why it's not a huge discussion...yet. Notes: Hx shows short and distort x 4k+.
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