The latest Citylets Report on the residential rental market covers their analysis of Q4 2015. It is worth noting that this only covers rental prices on new advertised properties. - it doesn't include rents on existing lets.
Annual growth in Scotland has slowed from 2.9% to 2% year on year, largely as a result of advertised rents in Aberdeen falling by 15.9%.
Edinburgh and Glasgow have seen rental rises in contrast to this of 5.7% and 4.2% respectively.
Edinburgh has now claimed the "crown" as Citylets puts it, of highest average advertised rent in Scotland, overtaking Aberdeen. Averages are not that relevant as anything other than for analysis of trends but delving into the figures for Edinburgh suggest that there is a real danger of rent rises continuing at an average of 5% a year. With wages rising more slowly rent rises on this scale may become unsustainable.
However, anyone considering this as argument for rent control misunderstands the economics of the market. Capital values of houses in Edinburgh are rising fats and if anything rents are lagging behind. Anyone trying to buy a new property to let out will know that it is getting harder and harder to achieve a reasonable gross yield of between 4 and 6%. Anything less than this makes it difficult to invest as the costs of management are higher than for other investments reducing net yields.