been when demand was lower; if service quality (rather than quantity) follows diminishing returns to labour input, a general demand for a higher service quality automatically produces a reduction in per-capita productivity. A typical labour market pattern is that high-GDP countries have a higher ratio of service-sector to traded-goods-sector employment than low-GDP countries. If the traded/non-traded consumption ratio is also correlated with the price level, the Penn effect would still be observed with labour productivity rising equally fast (in identical technologies) between countries. The protectionism explanation Lipsey and Swedenborg (1996) show a strong correlation between the barriers to Free trade and the domestic price level. If wealthy countries feel more able to protect their native producers than developing nations (e.g. with tariffs on agricultural imports) we should expect to see a correlation between rising GDP and rising prices (for goods in protected industries - especially food). This explanation is similar to the BS-effect, since an industry needing protection must be measurably less productive in the world market of the commodity it produces. However, this reasoning is slightly different from the pure BS-hypothesis, because the goods being produced are 'traded-goods', even though protectionist measures mean that they are more expensive on the domestic market than the international market, so they will not be "traded" internationally Trade theory implications The supply-side economists (and others) have argued that raising International competitiveness through policies that promote traded goods sectors' productivity (at the expense of other sectors) will increase a nation's GDP, and increase its standard of living, when compared with treating the sectors equally. The Balassa–Samuelson effect might be one reason to oppose this trade theory, because it predicts that: a GDP gain in traded goods does not lead to as much of an improvement in the living standard as an equal GDP increase in the non-traded sector. (This is due to the effect's prediction that the CPI will increase by more in the former case.) History The Balassa–Samuelson effect model was developed independently in 1964 by Béla Balassa and Paul Samuelson. The effect had previously been hypothesized in the first edition of Roy Forbes Harrod's International Economics (1939, pp. 71–77), but this portion was not included in subsequent editions. Partly because empirical findings have been mixed, and partly to differentiate the model from its conclusion, modern papers tend to refer to the Balassa–Samuelson hypothesis, rather than the Balassa–Samuelson effect. (See for instance: "A