a level of 60 ppm to 110 ppm. From NICMOS observations, [@Pont2009] derive a flat spectrum with a RMS of 190 ppm. In particular, they find no significant absorption in the 1.4 $\mu$m water band; instead, they find a flux excess of 142 ppm. Given the noise level, the data do not constrain the models. Another study of NICMOS transmission spectroscopy of HD 189733b, GJ-436b, and XO-1b finds no conclusive evidence for molecular features [@Gibson2011a]. Instead, residuals in the spectra are attributed to instrumental effects. The data themselves are the same as previous studies. The derived spectra are found to be dependent on the decorrelation procedure, necessary to remove instrumental noise. An answering comment from @Deroo2010 emphasizes in particular that a good decorrelation can not be achieved without considering the angle of the spectral trace on the detector. Indeed when that parameter is omitted, as in the spectrum of XO-1b reported by [@Gibson2011a], the result differs considerably from those in which it was included, [@Swain2008] and [@Tinetti2010], as we illustrate in the Appendix. More generally, @Gibson2011a [@Gibson2011b] consider the linear decorrelation method used in previous studies inadequately removes systematics, and that the instrument model should not be extrapolated between orbits.

