Dr. Harrison wants to test the effectiveness of the support group he runs for undergraduates who have drinking problems. He recruits a group of students who have been referred to the counseling center. He randomizes them to two groups: a structured-session group and an unstructured-session group. The structured-session group attends 10 structured support-group sessions at 8:00 a. m. on Fridays that are facilitated by Dr. Harrison. The unstructured-session group attends 10 unstructured meetings at 3:00 p. m. on Wednesdays that are facilitated by members of the group. Several of the participants in the structured-session group stop attending after just a couple of sessions. All the members of the unstructured-session group attend their meeting regularly. At the end of the 10 weeks, Dr. Harrison measures drinking behavior of the people who are still attending the groups. He finds the drinking behavior of people who attended all 10 structured-group sessions is less than the drinking behavior of people who attended all 10 unstructured-group sessions. Which kind of threat to internal validity should Dr. Harrison be concerned about?

selection-attrition threat                                  

Explanation:

In research methods, there are eight different threats related to internal validity.

Selection-attrition threat: The term "selection-attrition threat" is described as the propensity of a few individual's to be more likely to leave or drop out of a specific study as compared to other people. Therefore, this propensity of the individual can threaten the psychological experiment's validity.

In the question above, the given statement signifies the "selection-attrition threat".

the aksumite empire was an ancient kingdom located in what is now northern ethiopia from the period of 100 ad to 940 ad. its capital was the city of aksum. the kingdom established itself as one of the 4 great powers at its time, along with persia, rome, and china.

the kingdom was rich in goods like gold, iron, and salt. it established strong commercial ties with the regions governed by rome, egypt, and persia (arabia). aksum was a key location in this commercial network. trade was also facilitated with the introduction of the aksumite currency.

i am confused, what is the question? i can you out if you put it into more depth.