  The ellipticity function of cosmic voids exhibits strong dependence on the
amplitude of the linear matter power spectrum. Analyzing the most recent void
catalogs constructed by Foster and Nelson from the fifth data release of the
Sloan Digital Sky Survey, we measure observationally the ellipticity function
of giant galaxy voids. Then, we incorporate the redshift distortion and galaxy
bias effect into the analytic model of the void ellipticity function and fit it
to the observational result by adjusting the value of the power-spectrum
normalization with the help of the generalized chi^{2}-minimization method. The
best-fit normalization of the linear power spectrum is found to be
sigma_{8}=0.90+/-0.04. Our result is higher than the WMAP sigma_{8}-value but
consistent with that from the recent work of Liu and Li who have constructed a
new improved CMB map independently.
