Krahenbuhl & Blades conducted a study to investigate the influence of question repetition and question type on a child's ability to remember accurately. In the study, a total of 136 children aged five, seven and nine watched a fifteen-minute live presentation. One week later, the children were asked twenty questions which were repeated two more times during the interview. The accuracy of children's responses to unanswered questions decreased with repetition. They found that children were more likely to change an answer to an unanswered question than to a question to which they knew the answer. Overall, the children gave the same answers to only three-quarters of the repeated questions. The most common pattern of change involved children changing their response the second time a question was asked and then maintaining that response when the question was repeated. This study shows that repetition can have a negative effect on a child's eyewitness testimony, and thus render the use of children's eyewitness testimony about criminal activity ineffective. However, these studies may not be accurate in demonstrating how these factors influence children's eyewitness accounts because they lack ecological validity. They were all performed in a very laboratory-like environment, thus eliminating the nature of a child's memory. The children knew they were participating in a study and therefore may have done so