The following summarizes the percentage changes in operating income, percentage changes in revenue, and betas for four pharmaceutical firms.

Business groups Market Value of Equity Change in operating income Beta

Pharma corp $27\%25\%1\mathrm{.}00$

SynerCorp $25\%32\%1\mathrm{.}15$

BioMed $23\%36\%1\mathrm{.}30$

SafeMed $21\%40\%1\mathrm{.}40$

Calculate the degree of operating leverage for each of these firms.

Use the operating leverage to explain why these firms have different betas.