These moderating factors are not expected to be large and because they are relatively difficult to quantify they are the subject of ongoing research. One potentially effective solution to improving tranquillity, is to mask traffic noise or distract attention with an attractive water sound. A previous experiment has demonstrated that water generated sounds have the potential to improve the perceived tranquillity of gardens blighted by noise. A further study has demonstrated that litter has the potential to degrade an environment such that the tranquillity rating drops on average by one scale point.