What effect does multi-path propagation have on data transmissions?

Multi-path propagation happens when a radio signal reaches the receiving antenna by two or more paths, usually because it bounces off buildings, terrain, or the ionosphere. Because these paths have different lengths, the separate signals arrive slightly out of phase or at slightly different times. For data transmissions, these overlapping, delayed signals cause what is known as intersymbol interference, effectively smearing or scrambling the digital data bits together. Because the receiving equipment cannot properly isolate and decode the overlapping information, the overall error rate of the transmission will increase. Modifying transmission rates by a specific factor based on the number of paths (as suggested by the distractors) is neither practical nor how radios handle multi-path issues. Additionally, FM voice and data are not immune to multi-path distortion, making increased error rates the only correct outcome.