02312cam a22002417 4500001000600000003000500006005001700011008004100028100002300069245016200092260006600254490005100320500002000371520128800391530006101679538007201740538003601812700002101848710004201869830008601911856003701997856003602034t0068NBER20170820025033.0170820s1988 mau||||fs|||| 000 0 eng d1 aNelson, Charles R.10aSome Further Results on the Exact Small Sample Properties of the Instrumental Variable Estimatorh[electronic resource] /cCharles R. Nelson, Richard Startz. aCambridge, Mass.bNational Bureau of Economic Researchc1988.1 aNBER technical working paper seriesvno. t0068 aSeptember 1988.3 aNew results on the exact small sample distribution of the instrumental variable estimator are presented by studying an important special case. The exact closed forms for the probability density and cumulative distribution functions are given. There are a number of surprising findings. The small sample distribution is bimodal. with a point of zero probability mass. As the asymptotic variance grows large, the true distribution becomes concentrated around this point of zero mass. The central tendency of the estimator may be closer to the biased least squares estimator than it is to the true parameter value. The first and second moments of the IV estimator are both infinite. In the case in which least squares is biased upwards, and most of the mass of the IV estimator lies to the right of the true parameter, the mean of the IV estimator is infinitely negative. The difference between the true distribution and the normal asymptotic approximation depends on the ratio of the asymptotic variance to a parameter related to the correlation between the regressor and the regression, error. In particular, when the instrument is poorly correlated with the regressor, the asymptotic approximation to the distribution of the instrumental variable estimator will not be very accurate. aHardcopy version available to institutional subscribers. aSystem requirements: Adobe [Acrobat] Reader required for PDF files. aMode of access: World Wide Web.1 aStartz, Richard.2 aNational Bureau of Economic Research. 0aTechnical Working Paper Series (National Bureau of Economic Research)vno. t0068.4 uhttp://www.nber.org/papers/t006841uhttp://dx.doi.org/10.3386/t0068