ECMT2150 Intermediate Econometrics Assignment

The topic and information on the dataset

This assignment involves the application of a range of econometric methods to analyse how police should respond to domestic violence in order to reduce the number of repeat offences.

The issues are well summarised by Angrist and Pischke (2015, p.116): “abuse victims are often reluctant to press charges. Arresting batterers without victim cooperation may be pointless and could serve to aggravate an already bad situation... At the same time, victim advocates worry that the failure to arrest batterers signals social tolerance for violent acts that, if observed between strangers [as opposed to between domestic partners], would likely provoke a vigorous law enforcement response.”

We have a data set** used by Angrist and Pischke (2015) and Angrist (2006). The data set is named ‘Assignment.dta’.

• Download the data from the Assignment tab in our Canvas site.
• **Note: I have created a few different versions of the data and each student will have a link to just one of these. I have edited the data slightly for each version, but by enough that you need to work on your own data. If you work on one of your classmate’s data sets, you may answer one or more questions in the quiz incorrectly and lose marks or be referred to the academic integrity office.

This data was originally collected and analysed by Sherman and Berk (1984) and Berk and Sherman (1988). The original data come from the Minneapolis Domestic Violence Experiment (MDVE). The experiment was designed to assess the effect of arresting batterers or using a softer response on the re-occurrence of a domestic violence (DV) assault within 6 months at the same address.

The research design for the experiment randomly assigned two possible responses that the police officers attending the DV incident should follow. The police officers had to either:

• arrest the DV offender (the batterer), or
• use a softer response. In the softer response, Angrist calls it the “coddled” response, the police officers would either separate the DV offender by ordering the offender to stay away from the address for 8 hours or counsel/offer advice to the DV offender.

The incident had to meet certain criteria in order for the experiment to go ahead – namely, both the suspect and the victim had to be present when the officers arrived and the police officers had to have probable cause to believe that the cohabitant or spouse had committed a misdemeanor assault against a partner in the past 4 hours. Importantly, cases of life-threatening or severe injury (felony assault) were excluded.

So, we can see the two options the police officers had as two possible treatments, arrest or the “soft response”. Arrest usually meant a night in jail for the DV suspect. How was the randomization supposed to work in the experiment? Police officers had a physical pad of paper report forms that were randomly coloured and different colours indicated the police should follow a particular response to the incident. For the experiment, police officers were directed to act according to the colour of the report form on the top of the pad of forms. For example, if the top report form was green the police should arrest the DV offender and if the top report form was blue they should use the soft response on the DV offender.

Note that if the experiment had been carried our properly and the treatments (arrest or soft response) were truly randomised, we would be able to simply compare the probability of a reoccurrence of DV within 6 months for those offenders who were arrested to those who received the “soft response”.

But, in practice, police officers did not always follow the actions prescribed by the colour of the report form on the top of the pad. In some cases, the DV suspect was arrested even though the randomly assigned response by the report form directed the police to use the soft response.

Sometimes there were other circumstances that lead the police officers to elect to arrest the DV suspect. Other times, the police officers simply forgot their report forms. So, in practice, which treatment was delivered by the police officers (arrest or soft response) was not truly random.

Police officers had some role in choosing the response in at least some cases and so the choice they made may be related to other factors. I won’t say more here because I want you to think about this and answer some questions on it in your assignment.

So, we have a “broken” experiment. But all is not lost. IV methods can be a way to solve the problem and still identify the causal effect of the “soft response” versus arrest. In our data, for each DV incident, we have the following key variables:

• reoccur
• actual_soft
• assigned_soft
• actual_arrest
• assigned_arrest

as well as some useful other explanatory variables. See below for full details. We will use the variable assigned_soft as an instrumental variable for the variable actual_soft.