BLANKET INCAPACITATIVE SENTENCES CAN BE ALLOCATED BY IMPOSING THE SAME SENTENCE LENGTH ON ALL SERIOUS CRIMINALS OR BY GIVING DIFFERENT SENTENCE LENGTHS FOR DIFFERENT CRIMES (THE DIFFERENCE BEING THE FREQUENCY WITH WHICH A GIVEN CRIME OCCURS IN THE POPULATION, NOT ITS RELATIVE SEVERITY). THE MAJOR DIFFERENCE BETWEEN COLLECTIVE INCAPACITATION AND A JUST DESERTS MODEL IS THE BASIS FOR INCARCERATION. UNDER INCAPACITATION, INCARCERATION IS USED TO REDUCE CRIME. UNDER JUST DESERTS, SENTENCES ARE PUNISHMENTS AND ARE DISTRIBUTED ON THE BASIS OF JUSTICE. BOTH SYSTEMS CAN ALLOCATE THE SAME AMOUNT OF PUNISHMENT; THE CRITICAL DIFFERENCE LIES IN THE APPROACH TO DETERMINING WHO GETS WHAT PUNISHMENT. IN DECIDING WHETHER INCAPACITATION OR JUST DESERTS SHOULD GUIDE DETERMINATE SENTENCING, IT IS NECESSARY TO DETERMINE THE EXTENT TO WHICH EACH APPROACH REDUCES CRIME. IF COLLECTIVE INCAPACITATION DOES NOT REDUCE CRIME SIGNIFICANTLY BETTER THAN DOES THE JUST DESERTS MODEL, THEN THE LATTER SHOULD PREVAIL IN THE ALLOCATION OF PUNISHMENT IN A FREE SOCIETY. TO COMPARE INCAPACITATION AND JUST DESERTS, A 'VELOCITY OF CRIMINALITY' FORMULA IS DEVELOPED AND USED TO ANALYZE THE RELATIVE EFFECTIVENESS OF INCAPACITATION AND JUST DESERTS MODELS OF SENTENCING IN REDUCING CRIME AMONG A POPULATION OF 50,225 MALE AND FEMALE OFFENDERS RELEASED ON PAROLE DURING 1968 AND 1969. THE VELOCITY FORMULA, A RATIO BETWEEN THE NUMBER OF CRIMES COMMITTED BY AN INDIVIDUAL AND THE TIME THE INDIVIDUAL IS FREE TO COMMIT CRIMES, PROVIDES A BASIC UNIT OF MEASUREMENT FOR ASSESSING CRIME REDUCTION DUE TO INCAPACITATION. THE ANALYSIS SHOWS THAT THE JUST DESERTS SENTENCING MODEL IS 90 PERCENT AS EFFECTIVE AS COLLECTIVE INCAPACITATION IN REDUCING CRIME IN THE STUDY POPULATION. THE INCAPACITATIVE POTENTIAL OF DESERT-BASED SENTENCING APPEARS TO BE SUBSTANTIAL. ALTHOUGH THE ANALYSIS MERELY ILLUSTRATES THE QUANTIFIABILITY OF INCAPACITATIVE EFFECTIVENESS AND IS NOT TO BE GENERALIZED, IT DOES APPEAR THAT THE ADVANTAGES OF A JUST DESERTS SYSTEM OF PUNISHMENT MUST BE CONSIDERED. SUPPORTING DATA AND A LIST OF REFERENCES ARE INCLUDED.