Left panel: synthetic transit spectra, observations, and synthetic observations for the planet GJ 1214b. The orange points denote the observational data by Kreidberg et al. (2014), while brown points denote the observational data by Bean et al. (2010), Désert et al. (2011), Bean et al. (2011), Berta et al. (2012), Fraine et al. (2013). Synthetic spectra for the cloudy f_sed = 0.3 model (Model 3 in Table 2) are shown as red or purple solid lines for the case including Na₂S+KCl clouds or KCl clouds only. The clear model is shown as a teal line. A straight line model is shown as a thick gray solid line. The black dots show the synthetic observations derived for one (top) and ten (bottom) transits, re-binned to a resolution of 50. Vertical offsets have been applied for the sake of clarity. Right panel: p values of the Kolmogorov-Smirnov test for the residuals between the synthetic observation of the Na₂S+KCl cloud model and the straight line model fitted to these observations. The p value is shown as a function of N_transit for the three different instruments of Table 3. For every (instrument, N_transit) setup, a new straight line model is fitted to the observations. The black dashed line denotes our threshold value of 10^-3.