It is claimed that sporting events increase tourist numbers. They probably do. But by how much? The evidence that is usually cited is survey evidence from a study (usually paid for by a vested interest). Instead, let us look at the data provided by the Central Statistics Office. It decomposes visitor numbers into four groups (i) Holidays/Leisure/Recreation, (ii) Visits to friends & relatives, (iii) Business, and (iv) Other Reasons. The picture below shows the annual growth rates in three of these categories (the "Other" category was excluded because of the large variations). It is difficult to see massive changes in years with sporting events.
There will probably be a positive impact on visitor numbers from RWC 2023 but we should not overstate the impact. RWC 2023 is not the solution to all our problems. Us dismal scientists tend to warn about things like the broken window fallacy. Imagine a kid throws a stone through a window. Some would have you believe this kid should be celebrated. Look at all the extra spending it will generate. There will be extra spending on the replacement window. Then there will be extra spending on workers to replace the broken pane. The owner of the window shop and the window installers will then go and spend this extra money. This will generate a multiplier effect. The poor will be fed and homeless housed! And, what sort of policy does this provide for government? Break more windows.
(A previous post on the impact on visitor number for New Zealand in 2011 is available here.)