《外语教学研究方法》.ppt

Measurement Issues Another set of potential problems centers on the measures that are used: tested, questionnaires, observations, interview procedures, or any other means of quantifying language behavior. Since the result of a study are only as good as the data on which they are based, it is essential to make sure that the measures themselves are not introducing extraneous variables into the study. Three problems that the researcher should particularly watch for are the practice effect, the reactivity effect, and the instability of the measures or the results. Practice effect Practice effect ：essentially involves the potential influence of the measures on each other. Its strongest form occurs when the same test is given repeatedly in a study to determine if there are changes in performance. For instance, a study might be concluded to determine whether students are making gains in grammar during three weeks of intensive Spanish study. By giving the same grammar test before and after such learning, the researcher might attempt to determine how much the students improved during this period. The problem is that students often learn from their mistakes. So, formally or in formally, they may have cleared up any problems they had with the first test at the time of the second test, especially if subject expectancy was involved. Thus, any apparent gains in the scores on the second test may reflect the students’ actual growth in general proficiency in grammar or their learning the items on the particular test in question. If the practice effect is not controlled, it will obviously be impressible to separate these two variable. Thus, the results will be ambiguous and difficult to interpret. Reactivity effect In some language studies, a reactivity effect may occur when the measures themselves are causing a change in the subjects. One example of this effect might be an attitude questionnaire, in which the subjects actually form or solidity