Saturday, January 26, 2013

Does Population Size Predict Violence?

During a recent discussion on gun control, an individual made a seemingly reasonable assumption that crime rate was influenced by population size. I didn't disagree with that assumption and my gut told me that it was probably true. However, I decided I needed more data before I could come to that conclusion.

The first thing I did was narrow down what type of behavior I wanted to look at. In this case, I wanted to look at Violent crimes. This is violent crimes as defined by the FBI:

In the FBI’s Uniform Crime Reporting (UCR) Program, violent crime is composed of four offenses: murder and nonnegligent manslaughter, forcible rape, robbery, and aggravated assault. Violent crimes are defined in the UCR Program as those offenses which involve force or threat of force.

Source: FBI Website

So now that I knew what I wanted to look at I needed data to analyze. I found the following data on another FBI Page.

This data had to be cleaned up to only include population and total number of violent crimes per state.

State Population # of Violent Crimes
     Connecticut            3,580,709                       9,767
     Maine            1,328,188                       1,636
     Massachusetts            6,587,536                     28,219
     New Hampshire            1,318,194                       2,478
     Rhode Island            1,051,302                       2,602
     Vermont               626,431                          847
     New Jersey            8,821,155                     27,203
     New York          19,465,197                     77,490
     Pennsylvania          12,742,886                     45,240
     Illinois          12,869,257                     55,247
     Indiana            6,516,922                     21,626
     Michigan            9,876,187                     43,983
     Ohio          11,544,951                     35,484
     Wisconsin            5,711,767                     13,532
     Iowa            3,062,309                       7,826
     Kansas            2,871,238                     10,162
     Minnesota3            5,344,861                     11,825
     Missouri            6,010,688                     26,889
     Nebraska            1,842,641                       4,665
     North Dakota               683,932                       1,689
     South Dakota               824,082                       2,094
     Delaware               907,135                       5,075
     District of Columbia4               617,996                       7,429
     Florida          19,057,542                     98,199
     Georgia            9,815,210                     36,634
     Maryland            5,828,289                     28,797
     North Carolina            9,656,401                     33,774
     South Carolina            4,679,230                     26,760
     Virginia            8,096,604                     15,923
     West Virginia            1,855,364                       5,861
     Alabama5            4,802,740                     20,174
     Kentucky            4,369,356                     10,406
     Mississippi            2,978,512                       8,036
     Tennessee            6,403,353                     38,944
     Arkansas            2,937,979                     14,129
     Louisiana            4,574,836                     25,406
     Oklahoma            3,791,508                     17,243
     Texas          25,674,681                   104,873
     Arizona            6,482,505                     26,311
     Colorado            5,116,796                     16,383
     Idaho            1,584,985                       3,184
     Montana5               998,199                       2,670
     Nevada            2,723,322                     15,309
     New Mexico            2,082,224                     11,817
     Utah            2,817,222                       5,494
     Wyoming               568,158                       1,246
     Alaska               722,718                       4,383
     California          37,691,912                   154,944
     Hawaii            1,374,810                       3,949
     Oregon            3,871,859                       9,586
     Washington            6,830,038                     20,121

Next, I copied this data over to SPSS which is a data analysis software. For those of you unfamiliar with SPSS and statistical analysis in general, think of it as software that helps you draw conclusions based off mathematical formulas. These analysis help you make probability statements (similar to weather predictions) to determine if there are relationships or differences.

I will be helping you (the reader) determine what we can conclude from the SPSS outputs.

Before I ran the analysis I was aware of certain limitations with these data. First, there are many things not being taken into account. To begin with, we aren't taking into account how many cities are in each state, the rate of poverty per state, amount of land, or other variables which could easily moderate any data and change the conclusions we draw from this given data set. Basically, we are working within limitations.

On to the analysis...

ANOVA Stands for Analysis of Variance. The important information from this table is the column all the way to the left under Sig. This stands for "significance". Basically what you can interpret from the .000 is that there is less than .01% chance that the population and number of violent crimes are not related.

Adjusted R Square is the value we want to look at in this table. Roughly what this translates to is that about 95% of violent crimes can be predicted by a change in population. When population increases, so too does the number of violent crimes. However, this does NOT mean that population increase CAUSES increases in violent crimes, only that you can predict an increase (with a very high degree of certainty in this case) in violent crimes.

I intend to analyze some more data soon. For example, I'd like to see how states with strict gun laws compare to states with less strict gun laws. This will take some time, stay tuned.

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