I'm just reading some statistics.
Last year there were 3000 observations, this year there are only 1000. This is described as showing a "fall by a factor of 3".
This phrase doesn't ring true. If a factor of 3 is a 1/3, then a fall by a third would be down to 2000. So the phrase is meant to represent a fall to a third.
Am I right in thinking the phrase 'by a factor of' can only refer to an increase?