Analysis of Competing Hypotheses Dr Michael Townsley School of Criminology and Criminal Justice, Griffith University
21–27 April 2014 / International Summit On Scientific Criminal Analysis
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Outline
Defining What Analysis Is
Systematising Good Analysis
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What Do We Mean by Analysis? Analysis is not simply descriptive. It must include some component of reasoning, inference or interpretation. Regurgitating numerical values or summarising the situation is not analysis Need a system for doing this, comprising: • Appropriate theory • Methods to generate and test hypotheses
A system will allow you to generate knowledge about the criminal environment.
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Outline
Defining What Analysis Is
Systematising Good Analysis
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Generating and Testing Multiple Hypotheses
Need a way of coming to a decision: 1
document the characteristics of the problem (the symptoms)
2
derive convincing explanations for how the characteristics generate the crime problem (multiple hypotheses)
3
try to falsify these explanations.
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Documenting the Symptoms of a Crime Problem
Use Ekblom (1988) compendium question: the core of the analysis can be summarised in a compendium question: what offences occurred; where, when, under what circumstances and by what method were they committed; and who or what was the victim or target? The answer to the question can contribute to an understanding of the crime pattern, the criminal opportunities that underlie it, and the scope for prevention.
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Generate Explanations for the Problem
1
use environmental criminology theories (explicit)
2
ask police officers and other public servants what is causing the problem (implicit/experience)
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Test Multiple Hypotheses
Analysis of Competing Hypotheses (Heuer, 1999) is a technique developed in intelligence circles for analysts to avoid the major cognitive biases while assessing multiple hypotheses. Adapted for crime analysis by Townsley et al. (2011).
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Cognitive Biases
Three pervasive cognitive biases: 1
Availability bias (e.g. vividness effect)
2
Search satisficing (premature closure)
3
Confirmation bias
ACH attempts to reduce their influence in decision-making.
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ACH in 8 Well Defined Steps 1
Identify the possible hypotheses to be considered.
2
Make a list of significant evidence and arguments for and against each hypothesis.
3
Prepare a matrix with hypotheses across the top and evidence down the side.
4
Refine the matrix. Reconsider the hypotheses and delete evidence and arguments that have no diagnostic value.
5
Draw tentative conclusions about the relative likelihood of each hypothesis.
6
Analyse how sensitive your conclusion is to a few critical items of evidence.
7
Report conclusions. Discuss the relative likelihood of all the hypotheses, not just the most likely one.
8
Identify milestones for future observation that may indicate events are taking a different course than expected. 10 / 23
ACH Example
There is a concentration of vehicle crime in a shopping centre. Analysis shows the typical vehicle that get stolen is a lower end vehicle and is recovered within 48 hours. The incidents occur mainly in the afternoon and during school holidays. Theft sites cluster in one particular car park in the complex. This car park is also host to other crimes (theft of vehicles, criminal damage, etc).
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Step 1: Identify the possible hypotheses to be considered
1
vehicles are stolen that are easy to steal (low effort)
2
vehicles are stolen where there is little security (low risk)
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Step 2: Make a List of Significant Evidence and Arguments for and Against Each Hypothesis.
Symptoms in red There is a concentration of vehicle crime in a shopping centre. Analysis shows the typical vehicle that get stolen is a lower end vehicle and is recovered within 48 hours. The incidents occur mainly in the afternoon and during school holidays. Theft sites cluster in one particular car park in the complex. This car park is also host to other crimes (theft of vehicles, criminal damage, etc).
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Step 2 continued
This gives us: 1
mainly in the afternoon
2
lower end vehicle
3
they are recovered within 48 hours
4
cluster in one particular car park in the complex
5
also host to other crime types
6
during school holidays
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Step 3: Prepare a Matrix With Hypotheses Across the Top and Evidence Down the Side.
H1
H2
mainly in the afternoon lower end vehicle they are recovered within 48 hours cluster in one particular car park in the complex also host to other crime types during school holidays
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ACH Download A cross platform application of ACH1 exists
1
http://www2.parc.com/istl/projects/ach/ach.html
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Step 3 continued: Determine Diagnosticity A row at a time, determine if the Evidence confirms, disconfirms or is neutral to the Hypothesis
mainly in the afternoon lower end vehicle they are recovered within 48 hours cluster in one particular car park in the complex also host to other crime types during school holidays
H1
H2
-
+
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Step 3 continued: Determine Diagnosticity
mainly in the afternoon lower end vehicle they are recovered within 48 hours cluster in one particular car park in the complex also host to other crime types during school holidays
H1
H2
+ +
+ -
-
+
+
+ +
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Step 4: Refine the Matrix. Reconsider the Hypotheses and Delete Evidence and Arguments That Have No Diagnostic Value.
mainly in the afternoon lower end vehicle they are recovered within 48 hours cluster in one particular car park in the complex also host to other crime types during school holidays
H1
H2
+ +
+ -
-
+
+
+ +
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Step 5: Draw Tentative Conclusions About the Relative Likelihood of Each Hypothesis. The column with the least inconsistencies is the most likely, not the one with the most consistencies.
mainly in the afternoon lower end vehicle they are recovered within 48 hours cluster in one particular car park in the complex also host to other crime types Total
H1
H2
+ +
+ -
-
+
–3
+ –2
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Remaining Steps in ACH
Step 6: Analyse how sensitive your conclusion is to a few critical items of evidence. Step 7. Report conclusions. Discuss the relative likelihood of all the hypotheses, not just the most likely one. Step 8. Identify milestones for future observation that may indicate events are taking a different course than expected.
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Summary: Analysis Principles
• Identify symptoms using Ekblom’s compendium question • Pose multiple explanations of the problem • Use ACH as way to judge between different explanations • Use the scientific method–try to disprove explanations
rather then confirming them
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Bibliography I
Ekblom, P. (1988). Getting the Best out of Crime Analysis. Crime Prevention Unit. Home Office, London, UK. Heuer, R. J. (1999). Analysis of Competing Hypothesis, chapter 8, pages 95–110. Center for the Study of Intelligence, Central Intelligence Agency, Langley, VA. Townsley, M., Mann, M., and Garrett, K. (2011). The Missing Link of Crime Analysis: A Systematic Approach to Testing Competing Hypotheses. Policing, 5(2):158–171.
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