Methods of operating nonvolatile memory devices include testing strings of nonvolatile memory cells in the memory device to identify at least one weak string therein having a higher probability of yielding erroneous read data error relative to other strings. An identity of the at least one weak string may be stored as weak column information, which may be used to facilitate error detection and correction operations. In particular, an error correction operation may be performed on bits of data read from the strings using an algorithm that modifies a weighting of the reliability of one or more data bits in the bits of data based on the weak column information. More specifically, an algorithm may be used that interprets a bit of data read from the at least one weak string as having a relatively reduced reliability relative to other ones of the data bits.