Answer Part One
Sourcebook of criminal justice statistics Online
http://www.albany.edu/sourcebook/pdf/t412008.pdf

Table 4.1.2008

Estimated number of arrests a

By offense charged, United States, 2008

Offense charged
Total b 14,005,615
  • Murder and nonnegligent manslaughter 12,955
  • Forcible rape 22,584
  • Robbery 129,403
  • Aggravated assault 429,969
  • Burglary 308,479
  • Larceny-theft 1,266,706
  • Motor vehicle theft 98,035
  • Arson 14,125
  • Violent crime c 594,911

aData are based on all reporting agencies and estimates for unreported areas.
bBecause of rounding, figures may not add to total. Total does not include suspicion.
cViolent crimes are offenses of murder and nonnegligent manslaughter, forcible rape, robbery,
and aggravated assault.
dProperty crimes are offenses of burglary, larceny-theft, motor vehicle theft, and arson.
Source: U.S. Department of Justice, Federal Bureau of Investigation, Crime in the United
States, 2008, Table 29 [Online]. Available: http://www.fbi.gov/ucr/cius2008/data/

Quote Originally Posted by SadisticNature View Post
While you're at it you could try and find data on random stops. Police tend to be more suspicious of black people, so there are a far higher rate of random stops, and a far higher rate of searches at the border etc.

I have several acquaintances who smoke marijuana, 4 of whom took their personal amounts across the border, the three white guys weren't searched, the one minority was. Admittedly this is only an anecdotal case, but if stuff like this plays out in the larger data, then its quite likely blacks are not necessarily committing more crimes but rather are being treated with suspicion and hence are caught more frequently.

So looking it how arrests compare to convictions wouldn't show you the larger picture of what level of crimes are being committed. It would only show you what level of crimes are being caught. Assuming a random sampling is certainly problematic as there is strong evidence of bias. Take for instance racial profiling:

The idea behind it was that blacks committed a higher percentage of crimes, so if a police officer has two suspicious people (one white, one black) fleeing the scene of a crime and can only chase one of them they go after the black guy. There are several possibilities for what actually happened here:

Case (i): The black guy did it. They likely catch him and prosecute.

Case (ii): The white guy did it. He escapes the initial scene, and chances are somewhat poor that they track him down to catch him and prosecute.

Case (iii): They were accomplices. The black guy likely gets caught and is prosecuted. He may or may not turn over his accomplices.

So if you have a police force that responds to a chase scene in this way, you would have bias in your data. The white guy is far more likely to not be caught for this crime than the black guy.