Today is a special day! First off, it's the 9th day of the 9th month of the year (20)09 aka 09/09/09. Taking time into account, it's getting even better at 09:09:09 in the morning (and also in the evening for those working with a 12-hour time format). Although this is pretty cool in itself (yes I'm a geek), it's getting even better for me personally: Today is the day I become 9.999 days old! So I'm 9.999 days old, on 09/09/09 on 09:09. That are 9 9's, how is that for a coincidence?
Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.