Simulation of an Artificial Society with crime and

punishment José Roberto Iglesias,

Instituto de Física e Faculdade de Ciências Econômicas, UFRGS,

Porto Alegre, Brasil

econofis’10, são paulo, march 2010

Co-authorsCo-authors

• Viktoriya Semeshenko (Buenos Aires)• Jean-Pierre Nadal (Paris)• Mirta B. Gordon (Grenoble)

Gordon, Iglesias, Nadal, Semeshenko, Crime and Punishment: the economic burden of impunity, European Physical Journal B 68, 133–144 (2009)

Crime is as old as Crime is as old as humankind humankind “Passional (non-rational) crimes”:

a) Cain and Abelb) Don José and Carmen

Economic crimes a) Jacob and Esaub) Ronald Biggs and the Great Train

Robbery (8 august 1963)c) Bernrad Madoff and “financial

pyramids”(2009)

Crime is as old as Crime is as old as humankindhumankind “Passional (non-rational) crimes”:

a) Cain and Abelb) Don José and Carmen

Economic crimes a) Jacob and Esaub) Ronald Biggs and the Great Train

Robbery (8 august 1963)c) Bernrad Madoff and “financial

pyramids”(2009)

Crime is as old as Crime is as old as humankindhumankind

Multidisciplinary explanations and Multidisciplinary explanations and “solutions” for crime: philosophy, “solutions” for crime: philosophy,

law, sociology, ethics, economics...law, sociology, ethics, economics...

Modeling crime… and punishmentModeling crime… and punishment

Crime and punishment: Crime and punishment: the economic burden of the economic burden of

impunityimpunity The main hypothesis of the model:Crime, particularly economic crimes – stealing, robbery -

has an economic mobile.Each person is characterize by an “honesty” coefficient

that, when high, has dissuasive effect of the decision of committing an offense.

This “honesty” label is a global characterization of education, risk-aversion, fear, moral standards, fear, etc…

The probability of punishment depends on the stolen amount.

Offenders are punished, if caught, with fines an prison, both proportional to the stolen amount.

The average honesty of the population changes as a function of the perception of the society of the level of control of criminality.

Becker’s UtilityBecker’s Utility

(exp)(exp) BootyfWpBootyU kcast

)(BootyE

HU

k

k

ep

We add the “honesty” factor as an additional constraint

)()( BootyEfWpBootyEU kcast

Initial configurationInitial configuration• Each agent i is characterized by

a monthly wage Wi [Wmin,Wmax] triangular, [1,100]

a time-dependent honesty index Hi [Hmin,Hmax] triangular, [0,100]

When and how a crime is When and how a crime is committed?committed?

Criminal attempts

At each attemptselect potential criminal k and a victim v

success of the attempt depends on k’s honesty and the expected gain or booty* (cf. *G.Becker, P. Shikida)

If the crime is performed the offender gets S and the victim losses S

So that

• Crime: k robs a victim a random amount – S ≤ Kv !

H

NNmA inmates

11)(

WfWpWU kcast 55

WS 5vWrndS 10

W

U

H

H

k eepk

5

Arrested offenders and Arrested offenders and punishmentpunishment

Probability of punishment:• p0 – … of small offences

• p1 – … of large offences

Offender k goes to prison for months

Retribution: Offender k pays a fine f x S,

W

SS

e

pppS

1

)( 101

WS /1

Monthly resultsMonthly results

• Simulation setting:• N=1000, 240

months, Nc=5%• S=r*10*Wv, f=0.25S

• Various p0, p1

Crime and punishment: Crime and punishment: resultsresults

averages over 240 months

Left: With prison after-effects Right: Without

Wealth and Gini coefficientWealth and Gini coefficient

The Cost of PenaltiesThe Cost of Penalties

Histograms: WealthHistograms: Wealth

CorrelationsCorrelations

HysteresisHysteresis

What happens if the probability of punishment What happens if the probability of punishment changes in time?changes in time?

ConclusionsConclusions There is a first order phase transition in the criminality as a function of the probability of punishment This transition is accompanied by changes in the assets and inequality of he full society. Honesty coefficient (education) is an essential ingredient, along with the economic motivation of crime Punishment is not just fines and prison but also economic aftereffects. The after-effects of prison may increase criminality. If prison do not recover the offenders, crime is the only issue

Ongoing and upcoming…Ongoing and upcoming…• Rehabilitation: effects of incarceration on

honesty indexes and wages• Treatment of recidivism• Underlying networks (social and criminal)• Comparison with the empirical data

• Data from Rio Grande do Sul: correlations between size of the city, average education and criminaliry.

• Shikida interviewed inmates in Paraná: Economic crime is the rule. But criminality seems not to be correlated with poverty

• It is difficult to obtain the fraction of punished crimes to evaluate p0 and p1

Muito obrigado por Muito obrigado por vossa atençãovossa atenção

www.if.ufrgs.br/~iglesias

«The degree of civilization in a society can be judged by opening the doors of its prisons»(F. M. Dostoievski: F. M. Dostoievski: House of the DeathHouse of the Death)