Interesting idea. We have to decide what multiple of 1.04 is ‘suspicious’. Is 1300 suspicious, for example, being 1.04 x 1250 ? It might well not be. On the other hand, if we insist on ‘odd’ numbers like 1352 = 1.04 x 1300, we are probably discriminating too much. Integer multiples of 10 such as 1560 = 1.04 x 1500 are probably worthy of note, whereas we might treat integer multiples of 100 such as 1300 as ‘accidents’.
Bearing that in mind, I went back to the Daft rentals for the last two years. There is a background low level of suspicious numbers from well before the rent caps were introduced – numbers such as 1560 = 1.04 x 1500 and 3640 = 1.04 x 3500 crop up here and there. This could entirely by chance, or could be from when Baldy Noonan brought in PRSI on unearned income for PAYE workers in 2014. Maybe some accidental landlords will have passed this on to their tenants, but the frequency is too low to say anything for sure and my data only goes back to late 2015. The PRSI rate was 4%, unfortunately identical to the rent increase limit.
However, as you anticipated, we still get an interesting result when we graph the frequency of suspicious numbers post-rent-cap. As with my other graphs of rent levels, I’ve only included Dublin rentals with monthly asking prices. Expressed as percentages of total volume available to rent, the numbers are lowish but the trend is unmistakable: