Originally Posted by slim_slag
OK, if a week isn't long enough for you I'll run it for a month, that will give a lot more data points.
I wonder how my words "looking at prices across airlines for a single day out and a single day back" translate into a suggestion that we should look at prices for an entire month?
My point is that using a week is too long. Many people - like myself - usually have to go on day x and have to come back on day y. They're looking for the cheapest flights on those specific days only.
But when you did your last two comparisons, you used "the most expensive fares on each day for the round trip" to give "an idea of the maximum fares you might pay". The more realistic comparison, for leisure travellers, is to look at a single day each way, and to look at the minimum fares on those specific days.
That's how we came up (at the time) with the fact that on 14 Sep/18 Sep, BA was only £40 more expensive than FR.