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Figure 2: Constraint on the effective number of relativistic neutrino species, , by Stern et al. [26] using their measurements by the differential age method. Dotted line plots the 5-year WMAP [71] likelihood, dashed line plots the likelihood with WMAP and determined by Riess et al. [72], and the solid like the likelihood with WMAP, and data. Adding data helped refining the constraint to at 1- level. The improvement in the constraint by adding data is evident. Note that this figure displays the deviation of the statistic from its minimum inverted ( ). The intersections of the plots with the constant line correspond to 2- constraints.