Figure 2: Constraint on the effective number of relativistic neutrino species, , by Stern et al.  using their measurements by the differential age method. Dotted line plots the 5-year WMAP  likelihood, dashed line plots the likelihood with WMAP and determined by Riess et al. , 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.