Hermione and Luna conducted a study on the effects of marijuana on academic performance, and the effect of school on marijuana usage. They recruited 50 people from a well-known group of potheads at school, and 50 people from a well-known group of abstainers. At the beginning of the 2014 school year, they administered three measurements of key variables: (a) marijuana use - "how often do you smoke marijuana?"; (b) grade point average - "what were your grades for the previous semester"; and (c) relationship with their teachers - "in general, how good is your relationship with your teachers?" At the end of the school year, the researchers reassessed the three key variables: (a) marijuana use - "how often did you use marijuana in the past year?"; (b) GPA - "what are your grades for the current semester?"; and (c) relationship with teachers - obtained teachers' ratings of their relationships with the students in the study. By the end of the school year, 25 percent of potheads had dropped out of school (and thus out of the study), while none of the abstainers dropped out. Overall, the researchers found that people who use marijuana had significantly poorer GPAs and relationships with their teachers compared to non-users. However, the also found that marijuana users decreased their usage by the end of the school year, whereas a significant percentage of abstainers started using marijuana by the end of the school year. Thus, they concluded that marijuana negatively impacts people's scholastic achievements, and that school helps habitual users stop using marijuana but simultaneously causes people who never used marijuana to start using. Obviously, this study has many problems, particularly with its internal validity. Please describe how four of the eight threats to internal validity may have influenced the results of this study, and offer solutions for how to deal with these internal validity threats. In your answer, be sure to (a) describe each threat, (b) identify how each threat is present in the study, (c) explain how the threat would specifically impact the results of the study, and (d) offer one suggestion for how to solve or prevent each threat.

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The Answer of Hermione and Luna conducted a study on the effects of marijuana on academic performance, and the effect of school on marijuana usage. They recruited 50 people from a well-known group of potheads at school, and 50 people from a well-known group of abstainers. At the beginning of the 2014 school year, they administered three measurements of key variables: (a) marijuana use - "how often do you smoke marijuana?"; (b) grade point average - "what were your grades for the previous semester"; and (c) relationship with their teachers - "in general, how good is your relationship with your teachers?" At the end of the school year, the researchers reassessed the three key variables: (a) marijuana use - "how often did you use marijuana in the past year?"; (b) GPA - "what are your grades for the current semester?"; and (c) relationship with teachers - obtained teachers' ratings of their relationships with the students in the study. By the end of the school year, 25 percent of potheads had dropped out of school (and thus out of the study), while none of the abstainers dropped out. Overall, the researchers found that people who use marijuana had significantly poorer GPAs and relationships with their teachers compared to non-users. However, the also found that marijuana users decreased their usage by the end of the school year, whereas a significant percentage of abstainers started using marijuana by the end of the school year. Thus, they concluded that marijuana negatively impacts people's scholastic achievements, and that school helps habitual users stop using marijuana but simultaneously causes people who never used marijuana to start using. Obviously, this study has many problems, particularly with its internal validity. Please describe how four of the eight threats to internal validity may have influenced the results of this study, and offer solutions for how to deal with these internal validity threats. In your answer, be sure to (a) describe each threat, (b) identify how each threat is present in the study, (c) explain how the threat would specifically impact the results of the study, and (d) offer one suggestion for how to solve or prevent each threat.

Hermione and Luna Conducted a Study on the Effects of Marijuana