Arthrosis of the hip and knee: environmental causes in the first year of life? A study of 1405 cases of arthrosis in north Norway 1984-1989.
The association between month of birth and radiographically diagnosed bilateral arthrosis of the hip and/or knee was studied in 1405 cases at the University Hospital, University of Tromsø. In the total group no association was found in either sex for all arthrosis combined. In women with arthrosis of both hip and knee joints, however, the ratio between observed and expected showed a seasonal trend with a peak in the spring (1.48 for April births) and a low in the autumn and winter (0.39 for November births) (Test for seasonality: X2 = 9.48, d.f. = 2, p < 0.01). Low sunlight exposure prior to a crucial period in skeletal development is suggested as a possible cause.
A new proxy variable for the investment part of the initial Feldstein and Horioka model is proposed. We denominate it 'modified gross fixed capital formation'. It is derived by subtracting the imports of fixed assets included in an economy's gross fixed capital formation from the gross fixed capital formation itself. This way, the exclusively domestic part of an economy's investment is isolated. Applying it in the case of Norway, the aforementioned approach significantly reduces or even eliminates the high autocorrelation inherent in the initial Feldstein and Horioka model specification. Norway appears to be characterized by a high degree of international capital mobility.