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

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114Advances <strong>in</strong> Econometrics - <strong>The</strong>ory <strong>and</strong> Applications6.1.4 <strong>The</strong> White’s testThis test is a general test where I do not need to make any specific assumptions regard<strong>in</strong>gthe nature <strong>of</strong> the heteroscedasticity, whether it is <strong>in</strong>creas<strong>in</strong>g, decreas<strong>in</strong>g etc. <strong>The</strong> test onlytells us if I have an <strong>in</strong>dication <strong>of</strong> heteroscedasticity.2 20 : iH i<strong>The</strong> alternative hypothesis is not H 0 , anyth<strong>in</strong>g other than H 0 .<strong>The</strong> test can be divided <strong>in</strong>to several steps:1. Run an OLS on:y 1X1 ... X i i k ki iFrom this equation I get ˆi which is used as a proxy for the variance.2. Run an OLS on:ˆ ... ... 2 2 2i 0 1X1i kXki k1X1i kkXkk kk1X1iXk iWhere k is the number <strong>of</strong> parameters. <strong>The</strong> variance is considered to be a l<strong>in</strong>ear function <strong>of</strong> anumber <strong>of</strong> <strong>in</strong>dependent variables, their quadratic <strong>and</strong> cross products. Thus, the X:s is usedas a proxy for Z.3. Calculate an F-test:Restricted model:2 ' 'ˆi 0 i From this test the restricted residual sum <strong>of</strong> squares (RSS R ) is measured.<strong>The</strong> F-test is:WhereF=((RSS R -RSS U )/k) / (RSS U /(n-k-1))H0 : i 0 i1,2... k6.1.5 <strong>The</strong> ARCH Engel’s LM testThis is a test for AutoRegressive Conditional Heteroscedasticity (ARCH). <strong>The</strong> ARCHprocess can be modeled as:y X t t twhere the Variance <strong>of</strong> t conditioned on t i: Var( t \ t i ) = 0 + 1 t i1. Use OLS on the orig<strong>in</strong>al model <strong>and</strong> get: ˆt . Square it <strong>and</strong> use it <strong>in</strong> the follo<strong>in</strong>gunrestricted model:2 22. ˆ ˆt 0+ itii+t3. Test whether i = 0, for any i = 1, 2 , . . . By an F-test as before.2

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