[R] confidence interval or error of x intercept of a linear regression

[Thomas Lumley]

I should probably also add the health warning that the delta-method approach to ratios of coefficients is REALLY BAD unless the denominator is well away from zero.

When the denominator is near zero nothing really works (Fieller's method is valid but only because 'valid' means less than you might like for a confidence interval method, and the bootstrap is useful but not necessarily valid)

      -thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle