Answer: Does banning plastic bags actually help? How can you find out?

Sorry about the delay.  You can guess what I'm doing!  (Yes, I'm off SCUBA diving one more time.  Expect more exciting challenges about the natural history of islands.) 

However, my trip to <an unnamed location> is relevant to last week's SearchResearch Challenge.  

Plastic trash in the sea is a huge problem, albeit plastic nets are a bigger concern than plastic straws.  

But plastic bags are a bigger problem than you might think--they look like jellyfish to sea turtles, and as they break up into pieces, the plastic bag fragments look like other kinds of food, leading to fish and seabirds eating lots of plastic, which is both not nutritious and difficult to excrete.

As I mentioned, I was listening to one popular podcast about this topic on NPR (here's the transcript and the audio) pointing out that passing a law banning thin-film plastic bags in supermarkets seems to have actually caused an INCREASE in the number of plastic bags sold. 

That seems counterintuitive. And THAT's the kind of thing that makes me start doing a bit of research.  

After hearing this story about plastic bags, I naturally asked the following Research Questions: 

1. The story is clearly talking about a paper that Rebecca Taylor wrote.  Can you find that paper?  (What's the title?  Where was it published?)  

2. Once you find that paper, can you tell us where the data was collected from?  How representative is this data?  

3.  What do you call the counterintuitive effect when a partial regulation of consumer products results in the increased consumption of these products?  Is there a technical term we can use in future searches on this topic?  

4. How well has banning plastic bags worked in other places?  Can you find another study of a place where plastic bags have been banned?  How well did that work out?

1.  Finding that Rebecca Taylor paper wasn't too hard.  My query was: 

     [ Rebecca Taylor plastic bags ] 

which took me quickly to her web site, www.rebeccataylor.site/research  On her site you'll find on the effects of particular economic choices, including the paper we're looking for, "Bag Leakage: The Effect of Disposable Carryout Bag Regulations on Unregulated Bags"  
which appeared in the Journal of Environmental Economics and Management in January, 2019.  

2. Where is the data from?  The obvious place to look for the sources of the data is the original paper.  However, the original paper isn't available at the above landing page.  (Why not?  The paper is published at a journal that is owned and operated by the publishing house of Elsevier.  They run many journals.  That publisher sees it in their interest to not make the original paper available as an open access article. But fear not... read on!)  

So now what?  

Many authors (thankfully!) can't publish the final form publication of their paper, but CAN make a pre-final version available.  These are often called preprints and can be found without much trouble. The idea of a preprint is to get early feedback from colleagues.  It's often somewhat different from the final version.  However... in this case, the preprint is easy to find and tells us what we want to know--the origin of the data! 

I just did this search: 

     [ filetype:pdf  "Bag Leakage: The Effect of
        Disposable Carryout Bag Regulations
        on Unregulated Bags" ] 

That is, I used the filetype: operator to search for PDFs of the title of the paper, which I surrounded in double quotes to be sure I found ONLY this paper.  

This leads us to the paper at the SSRN (Social Science Research Network, which is, oddly enough, owned by Elsevier--the publisher that didn't share the open-access paper on their primary website).  

Reading through her paper, it's clear that she collected her data from California.  Quoting Taylor's paper: 

California provides an exceptional quasi-experiment for analyzing the effects of  disposable carryout bags (DCB) policies... [thus] policies have varied greatly in both their implementation dates and locations. It is important to note that local jurisdictions decide when DCB policies will be operative; the stores within a jurisdiction do not make this decision.

This is what makes California a great location for a "natural experiment."  By collecting data from those places that implemented a change AND those places that did not, it was possible to have an experimental group and a side-by-side natural control group that did not have any new DCB policies.  

In particular, the data comes from... 

... the Retail Scanner Database collected by AC Nielsen and made available through the Kilts Center at The University of Chicago Booth School of Business. 

... I use a subset of retail scanner data from participating stores in California between January 2009 and December 2015. ... I focus my analysis on food stores (i.e., supermarkets, grocery stores, and specialty food stores), mass merchandising stores (e.g., supercenters and big-box stores), and drug stores because these stores formats regularly sell non-food grocery items, such as trash bags. ... I include stores in [cities or counties] that meet the following criteria: (1) ... is no more than 50 miles from the coast, and (2) the jurisdiction is either an entire county or can be uniquely identified based on its 3-digit zip code. ... I limit the sample to the stores in 11 counties and 8 cities uniquely identified by their 3-digit zip code. This gives me a total of 546 stores. 

Looking farther down in the paper, there are charts and measures of the representativeness of the stores.  (See Table 1) It includes cities like Santa Monica in southern California, and counties like Alameda in northern California.  Income ranges from low to high, and population varies from 92K up to 1.6M.  

It's fairly diverse.  But it IS only in California. On the other hand, the data samples 546 stores, so this is a pretty good sample size.  


3.  What do you call the counterintuitive effect when a partial regulation of consumer products results in the increased consumption of these products?  Is there a technical term we can use in future searches on this topic? 

In this paper, Taylor gives us a term in the very first line:  "Leakage occurs when partial regulation of consumer products results in increased consumption of these products in unregulated domains."  

You might know what "leakage" means, but clearly, she's using it in a specialized sense.  THAT's the sign of a technical term.  (Much like the word boot in Computer Science meaning "to start up." One boots a computer at the start.)  

So, in this paper, leakage is used as a technical term meaning the effect of partly regulation something in order to decrease its use, but instead has the effect of increasing its use.  

Obviously, the title of the paper is a play on words:  bags leak when they're not supposed to, and "bag leakage" is the counterintuitive effect of increasing use when the goal is decrease.  

I did a search for [ leakage economics ] in Google Scholar to find other uses of this term, and found many.  I didn't know this, but it's a fairly common term that basically refers to capital or income that exits an economy or system rather than remaining within it. In economics, the term refers to the outflow from a circular flow of income model. 

Taylor is extending this definition slightly to talk about plastic bags leaking out of the recycling cycle.  As Taylor says, "If unregulated consumption [ of other plastic bags ] is easily substituted for regulated consumption [of banned bags ], basing the success of a regulation solely on reduced consumption in the regulated market overstates the regulation’s welfare gains..."  

In other words, it won't help to ban a product if another nearly-the-same product is easy to get.  

4. How well has banning plastic bags worked in other places?  Can you find another study of a place where plastic bags have been banned?  How well did that work out?

I started with the straightforward search: 

     [ how well do plastic bag bans work ] 

hoping to find articles about the effectiveness of plastic bag bans in other locations.  

It was pretty easy to find articles about banning plastic bags in Kenya (National Geographic, mixed success),  Massachusetts (Wired, mixed success), Maine and Vermont (Conservation Law Foundation, uncertain), Ireland (a levy, not a ban, Smithsonian, and the Ireland Institute for Environmental Policy, works well), and Denmark (EcoWatch, works well).  And so on.  It really is, pardon my pun, a mixed bag of results.  

After reading many of these articles, it's pretty clear that banning (or imposing a tax) DOES reduce the use of lightweight plastic bags, but it's not completely a clear win because people shift to other sources of bags.  That's Leakage in the sense that Taylor defines it, and so getting to the bottom of this requires a large-scale systems analysis.  Which is what Rebecca Taylor is trying to do in this paper.  

The key point of Taylor's paper might be in the last sentence of the abstract:  "policy evaluations that ignore leakage effects overstate the regulation’s welfare gains."  

It's easy to believe that a ban will solve the problem, but it also opens up the prospect of unanticipated consequences... which is where we started this discussion.  

My bottom line:  It's complicated, but the only way to really answer our Research Question is to do a full, sophisticated, extensive analysis of what the effects of a ban are... and the leakage that inevitably comes with it.   But it's an approach that has some promise!  

Search Research Lessons 

It's tempting to try to completely resolve the "do plastic bag bans work" question here, but I'll leave that to some enterprising graduate student in environmental studies to do that kind of work.  

For us, there are several points to make vis-a-vis SearchResearching for these kinds of things... 

1.   Finding the original paper was tricky, requiring a  search for a preprint.  Keep in mind that when you hit a paywall (where you'd have to pay for the paper), it's often possible to look around and find a copy of the paper available as a preprint.  It might not be 100% the same as the final version, but as you saw, in our case, it worked really well.  In our case, using filetype:PDF as a filter got us to that preprint. 

2. Finding the provenance of the original data is easy.. once you have the paper.  After you've got that, it's a simple matter of reading a bit to figure out from whence the data came.  (That's called its provenance.)  

3.  Watch out for technical terms.  Words that are used in a special way (or specialized context) can be useful for searching for other articles that help amplify / clarify what you're searching for... Check out "leakage" in this context.  

4. Looking for other contrasting studies is a great way to get context on what you're trying to understand.  In this post, we just used a simple question ("how well do plastic bag bans work")  as a query and found lots of other sources of information from other places.  


Hope you enjoyed this romp through online search methods!  

Search on!