There are many factors to buying a home. Comparing construction date to the property’s current condition versus required repairs is a (relatively) straightforward way of determining whether a prospective home buy is more of an investment or an asset. Looking at surrounding facilities and businesses is another factor to finding the perfect home. Are there schools? Are they any good? What kind of businesses are nearby? Is there a dynamic restaurant and shopping scene or are there "for lease" spaces? What is the crime rate like? And it is this final question that is the most difficult to answer, for a myriad of reasons.
To determine crime rates in a given population, there are two main data systems that are used by police departments. There is a Computer Aided Dispatch (CAD) system, which is essentially raw incoming data. They are emergency calls that come in and are then documented for filing. These include fire and ambulance requests so they initially have excess information that don't necessarily pertain to crimes. These reports are processed and filed into a Records Management System (RMS). This data is static and is used for reference and to cross check the performance of programs to see if they have been effective. So while they become a record of crime, they are also used as part of quality control efforts that police departments always have in motion.
So CAD is ongoing incoming data of reported crime that is open for updates as details emerge from each case. It is then recorded and becomes a part of the RMS data set and these bodies of data are sent to the FBI for filings on a volunteer basis. This is important to consider as well. Police forces aren't required to present all the crime data for national review and they also dictate whether or not to even report some crimes. Either the claims are deemed unsubstantial or the crime is filed in a category that doesn’t encapsulate the entirety of the crime. For example: If there is an assault and a robbery, it will be filed as an assault and not robbery, as the former is deemed more serious than the latter.
So we have crime data that is active and incoming and also data that is backlogged and updated on six-month intervals. This is done on a local level. There are national data sets as well but they are also sourced on a volunteer basis and can't be used conclusively to form any assumption on crime rates in isolated sample sizes. The National Incident Based Reporting System (NIBRS) is similar to the Uniform Crime Reporting Program (UCR, which is used by the FBI) but is updated more frequently. It has a uniform standard of crime filing so it is a step above UCR in terms of consistency. It should also be noted that while analysts use NIBRS and UCR, they are submitted voluntarily. To counter this there is the National Crime Victimization Survey.
The NCVS is the checks and balances to this whole crime data aggregation system. It is a survey that focuses on victim’s experiences. It gathers more details about the crimes and is done independent from police filings. Excluding murder, arson, and social/commercial crime, NCVS collects data on incidents that might not get filed due to hierarchical practices. It does a general, large sample size. Since 1973 a survey of 100,000 people, from the ages 12 and up, are collected twice a year for three years. It's careful to not scrutinize on any basis of protocol or bias. It is a general sampling that gives analysts an example of a larger whole. This data is for very general application as it can't be used to draw any conclusions on any specific region or demographic. It's mostly used by social scientists, but that doesn't mean it's not something worth checking out.
So when you're viewing crime statistics, you're either looking at data that is report-based, filtered through a hierarchy of filing protocols and is subject to change or updating, or you're looking at a catch-all survey of any and all crimes and claims that happened to individuals in a sample size. For the former, one should observe (if possible) the time of each incident as well as location. Arrests will often remove a case or incident that may be on a UCR but those arrests are something to scrutinize before drawing any conclusions. Crime data can be influenced by "arrest rates" but that doesn't take in account whether the crime was genuinely solved with a resulting conviction from that arrest.
What this really says is that crime data collection is a diverse science. There are many sources of authority that provide crime data that are subject to change and may differ greatly from national surveys. There are "known" crimes and they are filed (or not) based on a set of protocols that differ from state to state. So when looking at crime stats keep in mind where the sampling is from (city, state, country, etc.), what the system requirements are (lumping what is deemed as smaller crimes under larger crimes), and what the arrest-to-conviction rate is.
So if you're considering moving and want to get an informed idea of crime rates in a prospective area, consider what crime data is provided but take it with a grain of salt. This is not to say that whatever crime information you find is questionable, it's just that crime data is constantly in flux. There are many different forms and definitions of it and there are various, arbitrary ways in which it is quantified. The complexity of crime within a population is just that -- complex. So there is no end all way of staying on top of the data as it's coming in every second of the day. Be mindful of arrest/conviction rates and the nature of those crimes. That's all that it comes down to.
Turn on the news in any city or town and they most likely will report on a crime. The frequency of these reports typically are not an accurate reflection of crime in that area. Often, areas with low crime will report on it more as it is an uncommon occurrence and therefore more interesting. Conversely, a population with high crime rates will report them less, as it is commonplace and they don't want to be redundant. It's easy to get a misrepresentative impression of an area and its crime rates. As long as you know where the data is coming from (CAD, RMS, UCR, NIBRS, or NCVS) and you keep in mind conviction rates, you will have a better idea of crime rates than most. And of course, as always, it is up to you if you deem this information substantial or significant enough to be a part of your decision to move.
Christopher W. Bruce, Steven R. Hick, Julie P. Cooper, Exploring Crime Analysis: Readings on Essential Skills. (U.S.A: BookSurge Publishing, 2004), 158-162.