Work leading to currently used methods of seasonal adjustment began with the link-relative method of Persons (1919). His efforts motivated others in the 1920's and 1930's to consider the problem of seasonal adjustment. Macauley's (1931) development of the ratio-to-moving-average method was particularly important because it is the basis for the current Census X-11 method. Macauley and others borrowed the tool of moving averages from actuaries to smooth their data, rather than fit explicit functions to the data, because they felt that the trend and cycle components varied smoothly over time but they were, "... not necessarily representable throughout their length by any simple mathematical equation".