What is the misinformation effect and how does it relate to eyewitness testimony?

The misinformation effect, demonstrated by Elizabeth Loftus, occurs when misleading information presented after an event alters a person's memory of that event. In her classic study, participants who were asked "How fast were the cars going when they smashed into each other" gave higher speed estimates than those asked about the cars "hitting" each other. The word "smashed" planted a misleading suggestion that changed their memory.