Figure 1.

Comparison of score histogram versus theoretical distribution. Comparison of score histogram versus theoretical distribution. A randomly picked query spectrum is used to score peptides in NCBI's nr database. For this query spectrum, nine hundred unit intensity peaks were added to the processed spectrum to match S_us. In panel (A), the red staircase represents the histogram of scores computed using Eq. (1) with w_i = 1, while the blue line represents the theoretical distribution predicted from peptides with n = 44 theoretical peaks. In panel (B), scores computed using Eq. (1) with w_i(m_i) = exp(-Δ m_i) for peptides with different numbers of theoretical peaks are collected, resulting in the overall score histogram represented by the red staircase. The solid curve plots our fitting of the histogram using Eq. (17) where the fitting variables are β, γ ≡ n/(6⟨x²⟩ β²) and .