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9: What are some core research concepts?

The chapter covers the action of undertaking a study as part of the scientific method. Core concepts such as the distinction between policy research and applied research, external and internal validity, and reliability and generalizability are all summarized. The chapter also discusses samples from populations and the eligibility pool. The chapter provides advice on determining sample size, outlines seven sampling approaches researchers can use, as well as describing various survey options. There is also a discussion around how to select a research method, and a description of the many benefits to instituting a pilot study, along with some practical tips.

Glossary terms in this chapter

Policy research: Explores the impacts of different government or organizational policies and how they affect various outcomes.
Applied research: Tends to be more focused on the practical application of ideas to change the criminal justice system.
Validity: Relates to how much strength we can place in our conclusions and inferences.

Internal validity: Refers to the legitimacy of inferences we make about the causal relationship between two things. Strong internal validity in a causal relationship means changes in one thing effect or cause a change in the other.

External validity: The extent to which the findings of a study can be generalized to other situations, groups, or situations.

Reliability: Refers to whether you can consistently replicate the same results.

Generalizability: Generalizability speaks to the capacity of research to apply to other people or situations.

Sample size: Sample size is an important consideration if data are going to be sampled. Sampling means to draw a subset from a broader population. 
Population: A population is a group of individuals that share a common characteristic, such as residency of a city. These are the cases or units that comprise all individuals eligible for a study.
Eligibility pool: See population
Sample: A sample is a smaller, subset of the eligibility pool or population.
Sampling approach: The approach the researcher uses to choose the units of the population into the sample. 
Quantitative research: Involves measurable characteristics and frequently involves the use of statistical techniques to estimate how likely any observed differences between characteristics could have occurred by chance.
Positivist: Positivists lean towards the ‘science’ in ‘social science’ and favor quantitative methods to understand the laws and principles that influence human behavior and our social trends.

Mixed methods research: Mixed methods research combines quantitative and qualitative research techniques and approaches into a single study.

Surveys: Surveys are a method of asking people a range of questions about related research topics, to gain understanding of a larger population.

Closed-ended survey questions: Closed-ended survey questions limit the responses that a person can provide. The respondent can only select from the offered choices. 

Open-ended survey questions: Open-ended survey questions provide opportunity to answer and provide feedback more fully. These often comprise of open text field so respondents can type or write any answer they wish.

Dependent variable: The dependent variable is the variable being tested and measured. In evidence-based policing, it is the group, place, or population you want to impact. 

Pilot study: A preliminary project conducted at a smaller scale than the main project, so that the researcher can evaluate the feasibility and validity of the research design and methodology before embarking on the full-scale study.

Additional information and links

Core concepts in research

The opening story of the chapter (Not all research involves a knife fight) details a field work experience in Kensington, Philadelphia. Some bodyworn camera and station surveillance video of that incident can be found in the documentary Oscar One: Kensington Transit Corridor Overdose Response Study discussed farther down this page. 

It is common for there to be some confusion between internal and external validity of a research study. Even though using a medical scenario, this short description does a nice of job of explaining the difference. 

If you are looking to read more about sample methodology, there is a ten minute read here at Qualtrics. Qualtrics is a survey software company that creates an online environment for survey research. I've used it a number of times and found it to be very useful (caveat: Temple University has an account with Qualtrics). 

Pilot studies

If you have seen the companion video on pilot studies for this chapter (available on request to instructors and faculty only) then you will have seen details of two experiments, the Philadelphia Predictive Policing Experiment and the The Kensington Transit Corridor Overdose Response Study.

A web page with details of the Philadelphia Predictive Policing Experiment shows that the use of predictive policing found some benefits in terms of reduction in property crime, as well as some minor district-level crime control. There are three research articles linked to the study, most notably Ratcliffe, J. H., Taylor, R. B., Askey, A. P., Thomas, K., Grasso, J., Bethel, K., Fisher, R., Koehnlein, J. (2021) The Philadelphia Predictive Policing Experiment. Journal of Experimental Criminology, 17(1): 15-41. The article is available here

Oscar One

The Kensington Transit Corridor Overdose Response Study was a collaboration between SEPTA Transit Police and Temple University. There is one journal article available in reference to the research, Ratcliffe, JH & Wight, H (2022) Policing the largest drug market on the eastern seaboard: Officer perspectives on enforcement and community safety, Policing: An International Journal, 45(5): 727-740. You can download it here. 

There is also a 40 minute documentary about the project; Oscar One: The Kensington Transit Corridor Overdose Response Study. It features interviews, ride-along footage, and data on the study and the opioid crisis in Philadelphia. The documentary is available for free on YouTube. The video is also embedded below. 

Related Reducing Crime podcast episodes

Reducing Crime podcast episode

As an adjunct to the 40-minute documentary mentioned in the pilot studies discussion, Oscar One: The Kensington Transit Corridor Overdose Response Study, the Reducing Crime episode with Jennifer Wood provides more information on public health and policing.


Jennifer Wood (#32)

Jennifer Wood is a Professor of Criminal Justice at Temple University, and a criminologist with expertise in policing, regulation and public health. Our discussion covers the role law enforcement plays in the policing of mental health, addition and vulnerability, and the need to provide police with better structures, tools and options to help address these challenges. The detrimental impacts on officer health are also raised. 

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