SIR - S Pickup, referring to Britain leaving the EU (T&A letters, March 13), notes that we cannot know ‘the facts’ about an event in the future. However, it is unlikely we will know ‘the facts’ even after we leave.

The ONS, on behalf of the Government, estimates (with an error) many statistics such as GDP growth, numbers in employment, etc, that are used to guide policy.

To establish whether leaving the EU was good or bad for Britain, we will have to compare these statistics with some reference. There are two possibilities: an internal comparison where we compare the statistics for the post-EU Britain with a reference period when we were in the EU, or an external comparison where we compare the post-EU Britain with the EU as a whole or a country, for example France, within the EU. Both methods have serious flaws.

In any case, it will be irrelevant; we cannot continually hop into or out of the EU. Also, cognitive dissonance will mean that whatever the outcome, good, bad or indifferent, the more fervent the views held, the less likely are the protagonists to change their position whatever the evidence.

Ron Harding, Gawthorpe Lane, Bingley