By using which method of assignment of participants to treatment conditions, investigators increase the chances that participants' characteristics will be equally distributed across treatment groups?

Correct Answer: B

Rationale: By using random assignment of participants to treatment conditions, investigators increase the chances that participants' characteristics will be equally distributed across treatment groups. Random assignment helps reduce the likelihood of bias in the selection process and ensures that any differences between groups are due to the treatment and not pre-existing group differences. Sequential, systematic, and correlational assignment methods do not provide the same level of assurance in distributing participants' characteristics equally across treatment groups.

Correct Answer: D

Rationale: The concern Professor Higgins has regarding the findings of the longitudinal study is related to cohort effects. Cohort effects occur when a specific group of individuals experience a common event or circumstance that could influence the results of a study. In this case, the participants witnessing the terrorist attacks on the World Trade Center could have had a significant impact on their development and mental health outcomes, leading to cohort effects observed in the study. Choice A, 'practice,' is incorrect as it refers to the repeated performance of an activity to improve skill. Choice B, 'cross-sectional,' is incorrect as it involves data collection at a single point in time. Choice C, 'dropout,' is incorrect as it refers to participants leaving a study prematurely.

Correct Answer: B

Rationale: A sequential design permits researchers to check if cohort effects are operating. This design involves combining cross-sectional and longitudinal research, allowing for the comparison of different cohorts at different ages. By using this approach, researchers can determine if developmental changes observed are due to age or generation-specific factors. Therefore, a sequential design is valuable in addressing the potential influence of cohort effects on developmental outcomes. Choices A, C, and D are incorrect because a sequential design does not neglect diversity in developmental outcomes, is not necessarily less efficient than a longitudinal design, and can make both cross-sectional and longitudinal comparisons.

Correct Answer: B

Rationale: Ethical standards permit deception in research studies if investigators satisfy institutional review boards that such practices are necessary. Institutional review boards are responsible for ensuring that research studies comply with ethical guidelines and protect the welfare of study participants. Deception should only be used when necessary, and the board's approval indicates that safeguards are in place to minimize harm to participants. Choices A, C, and D are incorrect because ethical deception in research studies is not based on the age of participants, observing from behind mirrors, or obtaining informed consent without revealing the study's real purpose.