1. A researcher decides to test whether cooperative group testing (CGT) makes an increase in learning among college students. The researcher uses his two classes of EDR 751 to test whether CGT increases learning. Class A is the control group and they receive no special treatment. Class B will use CGT. The researcher tells class B that he expects CGT to increase learning, and that he will try it on them. He also tells class A that class B is trying a new method of teaching which is expected to increase learning, and that they will be used as a comparison group to see if they learn less.

Which threats are most likely to occur?

2. A researcher wishes to know whether dynamic or static assessment will increase teachers’ expectations for mentally handicapped (intellectually challenged) children. The researcher randomly assigns the teachers to two groups. The first group of teachers views the child via a dynamic assessment procedure. Following this viewing, both groups of teachers view the child via a static assessment. After this viewing, both sets of teachers complete an instrument designed to measure the teachers’ expectations of the child’s likely academic performance.

Which threat to external validity occurred?

3. A researcher is interested in determining whether Cooperative Group Testing (CGT) really increases academic performance (achievement). In each of the following studies he uses a Solomon Four Group design. In the first study, he looks at the effect of CGT on final exam scores in educational research classes. In the second study he looks at final class scores in several calculus classes to see if CGT had an effect. In a third study, which takes much longer, he looks at gains on the Iowa Test of Basic Skills for middle school students who used CGT for one year versus those who did not use CGT.

Which threat to external validity is the researcher most concerned with?

4. A researcher is interested in determining whether presentation method of contraceptive use will increase the use of contraceptives among sexually active teenagers. Aware of the possible threats to internal validity, the researcher decides to use the pretest-posttest control group design to test his hypothesis. Prior to giving the experimental and control groups of teenagers the treatment, the researcher asks the students to fill out a survey on their sexual activity and use of contraceptives. After completing the survey, the experimental group views a short video on contraceptive use and some of the dangers in not using contraceptives. The control group watches an episode of "Ren and Stimpy". The researcher then administers a second survey to the teenagers that is designed to measure whether they plan to use contraceptives in the future and he finds that a larger proportion of the experimental group say yes.

Which threat to external validity most likely occurred?

1. A researcher decides to test whether cooperative group testing (CGT) makes an increase in learning among college students. The researcher uses his two classes of EDR 751 to test whether CGT increases learning. Class A is the control group and they receive no special treatment. Class B will use CGT. The researcher tells class B that he expects CGT to increase learning, and that he will try it on them. He also tells class A that class B is trying a new method of teaching which is expected to increase learning, and that they will be used as a comparison group to see if they learn less.

Which threats are most likely to occur?

A: Selection-treatment interaction possible since intact groups were used--if randomly formed groups are not used, then selection-treatment interaction always possible. Since the researcher tells the groups what he expects to find, experimenter-effects are likely. Also, since each class knows which is the experimental and control group, reactive arrangements are also likely.

2. A researcher wishes to know whether dynamic or static assessment will increase teachers’ expectations for mentally handicapped (intellectually challenged) children. The researcher randomly assigns the teachers to two groups. The first group of teachers views the child via a dynamic assessment procedure. Following this viewing, both groups of teachers view the child via a static assessment. After this viewing, both sets of teachers complete an instrument designed to measure the teachers’ expectations of the child’s likely academic performance.

Which threat to external validity occurred?

A: Multiple-treatment interaction may occur here since two types of viewing (static and dynamic) were used with the experimental group.

3. A researcher is interested in determining whether Cooperative Group Testing (CGT) really increases academic performance (achievement). In each of the following studies he uses a Solomon Four Group design. In the first study, he looks at the effect of CGT on final exam scores in educational research classes. In the second study he looks at final class scores in several calculus classes to see if CGT had an effect. In a third study, which takes much longer, he looks at gains on the Iowa Test of Basic Skills for middle school students who used CGT for one year versus those who did not use CGT.

Which threat to external validity is the researcher most concerned with?

A: Given the special efforts to include three different types of achievement and students, the researcher was clearly concerned about specificity of variables--that is, the researcher did not want a critic to be able to say "well, you only tested this with college students," or "well, you only tested this with middle school students." So by included graduate students in educational research, undergraduates or high school students with calculus, and middle school students with general achievement as measured by ITBS scores, the research need not fear one claiming his study was too narrowly focused. Also, since the Solomon four group design was used, the researcher may also test for pretest-treatment interaction effects since groups with and without a pretest will be present.

4. A researcher is interested in determining whether presentation method of contraceptive use will increase the use of contraceptives among sexually active teenagers. Aware of the possible threats to internal validity, the researcher decides to use the pretest-posttest control group design to test his hypothesis. Prior to giving the experimental and control groups of teenagers the treatment, the researcher asks the students to fill out a survey on their sexual activity and use of contraceptives. After completing the survey, the experimental group views a short video on contraceptive use and some of the dangers in not using contraceptives. The control group watches an episode of "Ren and Stimpy". The researcher then administers a second survey to the teenagers that is designed to measure whether they plan to use contraceptives in the future and he finds that a larger proportion of the experimental group say yes.

Which threat to external validity most likely occurred?