Identify the threat to external validity in the following examples: a

Identify the threat to external validity in the following examples:

a. A teacher read research reporting great results from using a particular remedial reading program. She tried the program in her classroom but did not get the same results.

b. A teacher read about a new method of instruction that was very successful with regular classes. The method did not work when she tried it with her special education students.

c. A research journal reported that a new antismoking fi lm had brought about a signifi cant change in students’ attitudes. After viewing the fi lm, students expressed many more negative attitudes toward smoking than they had on a prefi lm measure. A teacher decided to use the fi lm with his middle school students but did not want to take time to administer the “pretest.” He administered an attitude scale following the fi lm but did not fi nd marked negative attitudes toward smoking.