1. A read method for a nonvolatile memory device, the method comprising: performing read operations on selected memory cells using a plurality of different read voltages; counting a number of memory cells in each of a plurality of threshold voltage bands based on data read using the different read voltages; deciding coordinate values of a probability density function corresponding to a threshold voltage of the selected memory cells based on the number of memory cells in each of the plurality of threshold voltage bands; obtaining coefficients of the probability density function based on the coordinate values; and deciding, as a read voltage of the selected memory cells, a threshold voltage of a coordinate point at which a slope of the probability density function is ‘ 0 ’.