Trend of Growth or Decline
For stations with a history of growth or decline, it is reasonable to expect this trend to continue. There are many possible reasons for these trends, such as demographic and employment changes.
Gating
Installation of ticket gates can significantly affect not only the usage figures at that station, but also those at neighbouring stations. The gates help to ensure that customers purchase tickets, but customers may also alter their travel patterns to avoid gated stations.
Reading the report that tells how the statistics were gathered for the 2004/2005 ticket sales figures ... the two comments above have some significance when reading Melksham.
a) A confirmation that, all things being equal, the ORR would expect to see traffic levels on a rapidly growing service continue to grow - confirmation that groth is a long term trend. In other words - the expert view applied to us would be to forecast the rises that I have assumed in work that shows brea-even and profit in a year or two ... but on the opportunity that First / DfT between them are throwing away.
b) On the gating - that's strong circumstantial evidence of significant fare evasion. Not of course in the case of Melksham inhabitants, all of whom are 100% honest

... but very probably a good explanation of why many of the Wesses Trains figures were very low compared to what was actually seen on the trains. High tech station controls aren't really cost effective on smaller statons that made up much of their network, so they were very much a victim of circumstances; I recall a very interesting discussion with one of their senior staff in which we discussed how (at engineering work times) it wasn't worth them providing a member of staff to accept payments at exceptionally quiet times (remember that bustitition cuts traffic to 25%) - collecting the fare would cost more than the fare collected.
For any accountant official who reads the latter as evidence that a service should be cut, can I point out that passengers joining a bus at 00:01 from Melksham to Westbury are few, but that doesn't mean that the bus won't have brought more people in to Melksham.