Friday, July 30, 2010

Research Proposals and Confusion about Dependent Variables

The following blog posting was originally uploaded to my hub here:

Having taught a year-long, two-course research component to Kean students for the past few years, it has become apparent that one of the most nagging issues for students is the dependent variable. Consider the following:

"My research proposal is about whether the death penalty reduces murder, so my dependent variable would be whether or not states have capital punishment, right?"


Research methods textbooks aren't necessarily helpful. Yes, they give the definition but even when my students do the reading, I can see from the blank stares that what they've read isn't sinking in. Here's a sampling of definitions for dependent variables from a few methods books:

From Singleton & Straits (2010), Approaches to Social Research: "The dependent variable is the one the researcher is interested in explaining and predicting. Variation in the dependent variable is thought to depend on or to be influenced by certain other variables. The explanatory variables that do the influencing and explaining are called independent. If we think in terms of cause and effect, the independent variable is the presumed cause and the dependant variable is the presumed effect."

From Maxfield & Babbie (2011), Research Methods for Criminal Justice and Criminology: "The variable assumed to depend on or be caused by another variable (called the independent variable). If you find that sentence length is partly a function of the number of prior arrests, then sentence length is being treated as a dependent variable."

And from my beloved Bachman & Paternoster (1997) Statistical Methods for Criminology and Criminal Justice: "Dependent variable - the variable that is being affected or influenced by another variable. It is often denoted as y. In a causal analysis the dependent variable is caused by the independent variable."

See a common theme in these definitions? The variables pertain to cause and effect. In the social sciences (like CJ, sociology and psychology), the effects are often people's behavior. In criminal justice field, those behaviors of interest would be..... crime! Crime. Antisocial behavior. Violence. Bad things that people do.

How do we measure our dependent variable crime? There are various ways, including arrests, victimization data (people reporting that they were harmed), and self-report criminal behavior (what people tell you they did criminally, for which they may or may not have been caught).

So to return to the original research question "Does capital punishment reduce crime?" the dependent variable would be crime, specifically states' arrest rates.
Other examples:

(1) Research question: Does the such-and-such conflict resolution program make schools safer?

Dependent variable: measure(s) of school safety such as # of fights, # of times the police are called to a school, # of suspensions for fighting.

(2) Research question: Does Colorado's anti-bullying law reduce bullying in school?

Dependent variable: measure(s) of bullying in school, such as data gathered through surveys of students about whether they've been bullied, done any bullying, or witnessed any bullying

(3) Research question: Does mandatory arrest by police reduce domestic violence (DV)?

Dependent variable: measure(s) of domestic violence reoffending (for instance)

(4) Research question: Which makes neighborhoods safer, having the police drive through the area or walk the beat on foot?

Dependent variable: measure(s) of neighborhood crime, such as home burglaries


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