The impact of comparability assessment and the use of internal standards. The relative increase of GFP expression calculated by the spectral counting method (black bar) was compared to that obtained by the external measurement using fluorescent (white bar). IS and CA represented the use of internal standards and comparability assessment, and the sign of plus (+) and minus (−) indicates the “the use” and “without the use” of method, respectively. For example, IS(+)/CA(+) meant the relative amount of GFP calculated with the use of internal standard and comparability assessment of replicates. The p-values were obtained by the Student t-test (see the Experimental procedures). (A) and (B) is the comparison of sample obtained at early and late exponential phase, respectively.