A University Alumni Office Conducted a Survey of Their Alumni

Multiple Choice

A university alumni office conducted a survey of their alumni to assess changes in attitudes toward the university over time.In the first year of the survey,the alumni office surveyed graduates from the year 2009.In the second and third years of the survey,graduates from the years 2011 and 2013 were surveyed,respectively.When examining the results of the survey to determine whether attitudes of the alumni changed over time,the alumni office should consider

A) the likely problem of attrition in their sample.
B) only the results of the 2013 sample.
C) the potential problem of noncomparable samples.
D) all of these