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ok, there's not really enough data points to do proper stats but lets give it a go anyway.
Lets consider the possibility that the ad campaign did nothing. Some ad campaigns are actually damaging so lets try to get an idea of how much it varies from month to month.
Mean = 50.5 Standard Deviation = 6.05
So about 1 and 2/3rds SD's above the mean.
Sure, October is a little higher than normal but not by much.
Or put another way, imagine that the ad campaign had been put into effect in April but actually did absolutely nothing. They would have seen an increase of 15.6 million along with a new record high.
The priori chance of ads increasing sales is high for good ad campaigns but as countless dot com bubble companies learned: it's entirely possible for advertising to get you absolutely nothing.
Remember that the priori is a fancy way of encoding your expectations into how you do calculations.
If you're trying to decide whether an ad campaign you've paid for actually worked a system of assessment which involves saying "well, I believed it should work in principle so I spent money on doing it in the first place and now I can confirm it worked partly because I believe it should work in principle"
Hm, thanks. It seems like I was misinformed about ads – I had the belief that they increase sales almost all of the time, which, based on what you said and a quick search. appears to have been totally false. With that and the 'largely' I missed, I'd now say the test was mostly correct.