This paper extends the simple errors-in-variable bound to the setting of systems of equations. Both diagonal and nondiagonal measurement error covariance matrices are considered. In the nondiagonal case, the analogue of the simple errors-in-variable interval of estimates is an ellipsoid with diagonal equal to the line segment connecting the direct least squares with a two-stage least squares estimate. For the diagonal case, the set of estimates under some conditions must lie within the convex hull of 2k points.

The three-factor, n-good model is displayed graphically and tested empirically. The three-dimensional endowment vectors and expansion paths are represented by points in an endowment triangle. Features of this endowment triangle determine relative factor returns, Rybczy nski and Stolper-Samuelson derivatives, output mixes, and the directi on of trade. The effects of mobile factors and nontraded goods are al so considered. Capital accumulation is shown to induce changes in out puts, trade, and the returns to factors that depend on the abundance of land relative to labor. Weak evidence for this 3 A n model is foun d in a 1978 U.N. data set on the value of output.

The Heckscher-Ohlin-Vanek model predicts relationships among industry input requirements, country resource supplies, and international trade in commodities. These relationships are tested using data on twelve resources, and the trade of twenty-seven countries in 1967. The Heckscher-Ohlin propositions that trade reveals gross and relative factor abundance are not supported by these data. The Heckscher-Ohlin-Vanek equations are also rejected in favor of weaker models that allow technological differences and measurement errors.