A study examined whether frequent use of digitall social media during adolescence is related with subsequent occurrence of ADHD symptoms. Researchers rated the frequency of digital social media use (high frequency or low frequency of use) of teens who were 15 or 16 years old and did not show symptoms of ADHD st the star of the study. They then followed the participants for two years and recorded whether or nor ADHD symptons appeared The results are shown in the table show. a) what are the cases in this study? b) what kind of sampling did the researcher do? Briefly explain. c) what is the explanatory variable? What type of variable is it? Explain. d) What is the response variable? Identify the variable type. Explain. e) What type of study was conducted? Briefly explain. f) Is it appropriate to conclude causation in this case? Explain