Keller and Yeaple (2003) also find positive and robust effects of inward FDI in the United States on productivity in US manufacturing plants between 1987 and 1996. Girma, Greenaway, and Wakelin (2001), using the firm data described above, find that there are spillovers and that they are greater for firms in sectors in which local firms are technologically comparable to the foreign firms. Labor productivity and total factor productivity spillovers are similar in size. As with wage spillovers, the accumulation of studies has eroded the basis for the hypothesis that the distinction between cross-section and panel data studies explains the wide range of findings.