Gross murder rates cannot be a valid and consistent method of measuring deterrence, for a variety of well know reasons (1).
As many anti death penalty folks, including academics, wrongly, present some gross murder numbers as a foundation for arguing against deterrence, I present this:
HISTORY: MURDER RATES AND EXECUTION CYCLES
Again, this is not how deterrence is measured (1), however . . . .
1. The United States has had double digit executions, annually, from 1984 - 2011 (3).
Murders are, now, at a 43 year low (2),
Murder rates are, now, at a 48 year low. (2).
It's not surprising that death sentences are at a 37 year low (3).
2. Double digit annual executions stopped in the US in 1964 and resumed in 1984 (3).
During that period, murders increased by 100%
murders in 1964 9,360 (2)
murders in 1984 18,670 (2)
3. There was a moratorium on all executions in the US from 1967 to 1977 (3).
During that period, there was a 56% increase in murders (2).
murders is 1967 were 12,240 (2)
murders in 1977 were 19,120 (2)
Capital murders may have dropped by 80% or more in Texas since 1991 (2).
Murder in combination with rapes and/or robberies makes up, by far, the largest percentage of death penalty eligible murders.
Murders have dropped 58%, rapes 20% and robberies 41% (2).
A much lower occurrence of rape/murders and robbery/murders equals a much lower number of death sentences.
The per capita rape/murders and robbery/murders will have dropped even more dramatically, because Texas has seen a population explosion during this period.
Murders rates have dropped 71%, rapes 46% and robberies 61% (2).
The drop in capital murders is but the most obvious and pronounced explanation for a drop in death sentences.
Contributions to that drop also include:
1) Plea bargains to life without parole (LWOP) , a plea only possible with the death penalty;
2) Two classes of murderers have been excluded from the death penalty, that being those under 18 and those with mental retardation; and
3) Depending upon conditions within individual jurisdictions, with a downturn in the economy, the up front costs of the death penalty may have caused some jurisdictions to offer either plea bargains or lesser than death penalty option trials, to a degree more than in the past.
1) a) "Death Penalty, Deterrence & Murder Rates: Let's be clear"
NOTE: There are some deterrence studies which find a reduction in murders, soon after executions. Howevewr, I am, primarily, dealing with murders and murder rates for any given year.
2) United States Crime Data, from FBI UCR
The Disaster Center is a convenient and reliable source for crime data
murders rapes robberies
1991 2652 9266 47900
2011 1126 7439 28395
dif 1526 1827 19505
less 58% 20% 41%
murders rapes robberies
1991 24,700 106,590 687,730
2011 14,612 83,425 354,396
dif 10,088 23,165 333,334
less 41% 22% 48%
Source: Disaster Center, from FBI UCR
3) Capital Punishment, 2010 - Statistical Tables, Bureau of Justice Statistics, Tracy Snell, Dec 2011, see Figure 1, page 1 and Table 8, page 12,
OF COURSE THE DEATH PENALTY DETERS
LIFE: MUCH PREFERRED OVER EXECUTION:
99.7% of murderers tells us "Give me life, not execution"
See sections C and D within
The Death Penalty: Saving More Innocent Lives
"DEATH PENALTY DETERRENCE CLARIFIED"
Innocents More At Risk Without Death Penalty