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No predictive model is going to be 100% accurate unless by chance. The nature of predictive modeling is to learn from the past and see into the future. Essentially, predictive modeling is just modeling. Think about why we use statistical models - so we can fit the data into a pattern of behavior and anticipate future results. It's all about how you use and interpret this model.
Crime analysts may use a tool similar to the following example on a robbery series:
|3/1/2005||Tue||--||18:30||1502 E Broadway||$1,120|
|3/8/2005||Tue||7||17:25||1454 S Main St||$1,130|
|3/12/2005||Sat||4||19:00||1903 S First St||$1,370|
|3/17/2005||Thu||5||20:00||1989 N Fourth St||$1,420|
|3/24/2005||Thu||7||20:25||1048 N Third St||$1,700|
|4/2/2005||Sat||9||21:45||1336 E Kimberly Ave||$980|
|1 St. Dev Earliest||7/16/2005||18:33|
|1 St. Dev Latest||7/20/2005||21:45|
|# of Days til Next||3.18|
Based on the frequency of the robberies and the amount stolen, the next predicted date is in 3.18 days. Now, would you tell your patrol officer that they can expect another hit in exactly that time? No. But you can use this information to provide a possible date range. You can also provide the most likely time for a robbery to occur. Past data helps us to identify patterns for the future but it is not always the rule to follow for future events. This data is used in conjunction with intelligence reports from patrols.
Data is concrete. It gives us the probability of future events occurring. Add in variables that you know will affect the probability, and you have a predictive model that is even less concrete. Explaining this to your "customer" should go something like this:
This is what happened [insert data here]. This is the probability of it happening again [insert probability here]. Based on the pattern, the next most likely event occurrence is [insert data range].
In conclusion, it's all about conclusions. You will not be able to give a definite "next step", though you can come pretty close. A marriage of data analysis and intelligence analysis will give you a higher probability of catching and preventing criminal actions.