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The Limits of Mathematics and NP Estimation in ... - Chichilnisky

The Limits of Mathematics and NP Estimation in ... - Chichilnisky

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80Advances <strong>in</strong> Econometrics - <strong>The</strong>ory <strong>and</strong> Applications<strong>and</strong> the UK st<strong>and</strong>s for those countries exhibit<strong>in</strong>g the average. Table 1 shows the 20-yearevolution <strong>of</strong> the self-employment rate with<strong>in</strong> the EU-15.1987 1995 2000 2007Austria - 10.8 10.5 14.4Belgium 15.3 15.4 13.6 12.8Denmark 9.2 8.4 8.0 8.9F<strong>in</strong>l<strong>and</strong> - 14.3 12.6 12.6France 12.7 11.6 10.0 9.0Germany 9.1 9.4 9.7 12.0Greece 35.4 33.8 31.3 35.9Irel<strong>and</strong> 21.8 20.8 16.5 16.8Italy 24.4 24.5 23.6 26.4Luxembourg 9.2 10.0 8.7 6.1Netherl<strong>and</strong>s 10.1 11.5 10.0 12.4Portugal 27.2 25.8 20.2 24.2Spa<strong>in</strong> 23.5 21.8 18.0 17.7Sweden - 11.3 9.8 10.6United K<strong>in</strong>gdom 12.5 13.0 10.9 13.8EU15 15.9 15.0 13.6 15.6Table 1. Self-employment rates (Eurostat Labour Force Survey). Note: Percentage <strong>of</strong> selfemployedpersons over total employed.Us<strong>in</strong>g a homogeneous database, we <strong>in</strong>vestigate whether differences exist <strong>in</strong> the pr<strong>of</strong>itability<strong>of</strong> school<strong>in</strong>g <strong>and</strong> experience, both between the two employment statuses, <strong>and</strong> across thethree sample countries. <strong>The</strong> database used <strong>in</strong> this work has been obta<strong>in</strong>ed from theEuropean Community Household Panel (ECHP), from 1994 to 2000, which providesabundant <strong>in</strong>formation about the personal <strong>and</strong> labour characteristics <strong>of</strong> <strong>in</strong>dividuals, <strong>and</strong> hasthe advantage that this <strong>in</strong>formation is homogeneous across the sample countries, given thatthe questionnaire is the same <strong>and</strong> the collection process is coord<strong>in</strong>ated by the StatisticalOffice <strong>of</strong> the European Community (EUROSTAT). Additionally, the application <strong>of</strong> paneldata techniques <strong>of</strong>fers some clear advantages over the traditional cross-sectionalapproaches. First, <strong>in</strong>dividual unobserved heterogeneity is controlled for. Second, biasesaris<strong>in</strong>g from aggregation, selectivity, measurement error, <strong>and</strong> endogeneity can be dealt with<strong>in</strong> an appropriate form. Third, dynamic behavior, such as the movements <strong>in</strong>to <strong>and</strong> out <strong>of</strong>self-employment, may be explicitly accounted for.<strong>The</strong> two usual estimators used <strong>in</strong> panel data, that is to say fixed <strong>and</strong> r<strong>and</strong>om effects, are,however, <strong>in</strong>adequate <strong>in</strong> this sett<strong>in</strong>g if the objective is to obta<strong>in</strong> consistent <strong>and</strong> efficientmeasures <strong>of</strong> the pr<strong>of</strong>itability <strong>of</strong> education <strong>and</strong> experience. Thus, the presence <strong>of</strong> time<strong>in</strong>variant<strong>and</strong> possibly endogenous regressors (e.g. education), would make it impossible toestimate their associated parameters when a time or mean-differenc<strong>in</strong>g approach, i.e. thefixed effects, is applied. Additionally, the probable correlation between these time-<strong>in</strong>variantregressors <strong>and</strong> the unobserved effects causes the r<strong>and</strong>om effects estimator to be <strong>in</strong>consistent.Altogether, this po<strong>in</strong>ts to the advisability <strong>of</strong> us<strong>in</strong>g a hybrid technique that lies between bothextremes. Moreover, the potential existence <strong>of</strong> measurement errors <strong>and</strong>/or endogeneityrequires <strong>in</strong>strumental variables (IV) to obta<strong>in</strong> consistent estimates <strong>of</strong> the coefficients. As aconsequence, the Hausman & Taylor (1981) estimator is the most adequate, s<strong>in</strong>ce it has been

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