I found data from Montgomery county, Maryland which in 2011 effected the Montgomery County Carryout Bag Law to charge shoppers 5¢ a piece for single-use carryout bags at retail stores..In Montgomery, unlike in California, 80% of the amount collected from the bags is due to the county..As a result Montgomery County has good data on their Bag Law program.Here, I examine the data to see what effect, if any, the Carryout Bag Law has had on buyer behavior..Ideally, we would compare a pre-treatment Montgomery (or a similar untreated county) to Montgomery after the bag tax was effected..However, we only have data from Montgomery, and only after the fact..So we’ll instead investigate the trend in bag use over time since the law was effected..I’ll discuss data preparation first..My R code and the data can be downloaded here..Feel free to skip to the takeaways at the end of the post!Brief Introduction to the Bag_Tax DataThe data contains 1303 unique vendors and their roughly monthly contributions to the bag tax..Each entry (row) is a unique contribution made by a vendor during a time period, indicated by the first and last day of the period..Entries report the number of bags sold and dollar amount collected, among other things (see Table 1 for a sample from the data. I didn’t include all the columns)..Data cleaning was quick: I removed entries which were dated before the law came into effect, and entries that appeared to be from the future (When I downloaded the data, the website reported that they had last been updated on Aug 9, 2018. Any entries after that were considered wrongly dated).. More details