Description

TUTORIAL 2
Please work on the problems before coming to class. In class, you will engage in group work.

A Case Study on Recycling Rates in Singapore
You are a student of a new course NEA1000 Environmental Matters of Singapore and you have been assigned to do a group project on recycling of Paper/Cardboard waste in Singapore with your classmates, Chuan and Tammy. The file recyclingstats.pdf was compiled by Chuan using data found on the National Environment Agency website. For the tutorial discussion, we assume that the data refers to domestic recycling only.

Recycled (‘000 tonnes)
Disposed (‘000 tonnes)
Total (‘000 tonnes)

Paper/Cardboard. Is Tammy’s claim correct? How can you reconcile her claim with your answer in (a)?

c. From the file recyclingstats.pdf, Tammy computed the rate of

% of waste recycled in… Households Shophouses Educational Institutions Petrol Kiosks Hawker Centres Places of
Worship
2012 3.9 9.1 10.2 8.9 5.6 14.3
2013 4.1 9.3 12.3 9.1 5.6 14.2
2014 3.8 9.7 15.6 8.7 7.5 15.6
2015 4.5 10.3 16.1 10.2 8.2 16.1
2016 5.3 10.1 16.9 11.2 9.3 15.2

Tammy decided to conduct a study to understand the prevalence of Paper/Cardboard recycling amongst NUS students. She stood at the main entrance of Town Plaza in front of the spiral staircase over a period of two weeks during her free time. Knowing that she would not be able to interview everyone who was going to walk past her, she decided beforehand to only survey one student out of every seven who walks past her, starting from the first person she sees when she arrives at the entrance. She collated the information she gathered in the data set recycling_survey.csv. Below is a brief description of the variables:
Variable Description
year The student’s year of study.
use_monthly The average monthly usage of Paper/Cardboard of a student.
• Often – At least once a day for the whole month • Sometimes – Once in two to six days inclusive
• Seldom – At most once a week, but at least once in two weeks
• Rarely – Less frequent than once in two weeks
recycle_monthly The average number of times a student brings his/her recycled materials to a designated recycling bin in a month.
stay_campus Whether a student stays on campus.
foreigner A student is a “foreigner” if he/she is not a Singapore Citizen or a Singapore Permanent Resident.

e. Chuan hypothesises that students who have a lower average monthly usage of Paper/Cardboard would bring their recycled materials to a designated recycling bin more frequently, as these behaviours both suggest that a student is more environmentally conscious.

He suggests considering an average monthly usage of Paper/Cardboard of a student to be “low” if the student’s response was “Rarely” or “Seldom” (otherwise, it is considered “high”); and considering a student to have “healthy” recycling habits if the student brings the recycled materials to a designated recycling bin more than twice on average each month (otherwise, it is considered “unhealthy”). What is the association between having healthy recycling habits and a high average monthly usage of Paper/Cardboard within Tammy’s data set?

g. Upon seeing what Chuan did, Tammy decided to explore the data set as well. She sliced the data set using whether a student is a foreigner as a third variable and analysed the association between recycling habits and the use of Paper/Cardboard. She then produced the following stacked bar plots:

Tammy claims that from her plots, Simpson’s Paradox is not observed, and thus “whether a student is a foreigner” is not a confounder in the association between recycling habits and the usage of Paper/Cardboard. Based only on Tammy’s plots above, is Tammy’s claim true?

h. “We can have a good understanding of recycling of Paper/Cardboard amongst NUS students from the study because 2000 students responded to the survey, and systematic random sampling was used,” Tammy asserts.
Would you agree with her assertion?