I do not know and I have no opinion but I strongly suspect
that the practice of charging or not charging DUI[1] may
vary a lot from State to State as I strongly doubt that
actual DUI varies so much among populations:
http://www.statisticbrain.com/number-of-dui-arrests-per-state/
Note that Wisconsin shows one per 140 persons and then next
door Illinois is rated 1:2621. I know that Illinois has a
history of vacated charges for DUI which are both
ridiculously expensive and also routine in the Chicago metro
area, but that rate seems unconnected to reality.
NJ with 1:362 versus NY at 1:773 are not as dramatic as a
comparison to DE at an unbelievable one to 4219 persons.
In sum, I believe there are significant factors we have not
considered. You can't make the case that a legal (by statue
or by prosecution or sentencing practice) could make that
magnitude+ sized difference.
[1] Perhaps reporting/not reporting?
p.s. I dropped that list into a spreadsheet with ratios.
State DUI Arrests in 2015 Population Size RATE
Alabama 14,991 4,802,740 320.4
Alaska 5,538 722,718 130.5
Arizona 39,746 6,482,505 163.1
Arkansas 11,707 2,937,979 251.0
California 214,828 37,691,912 175.5
Colorado 28,198 5,116,769 181.5
Connecticut 8,235 3,580,709 434.8
Delaware 215 907,135 4 219.2
Florida 61,852 19,057,542 308.1
Georgia 25,421 9,815,210 386.1
Hawaii 5,812 1,374,810 236.5
Idaho 11,850 1,584,985 133.8
Illinois 4,909 12,869,257 2621.6
Indiana 23,475 6,516,922 277.6
Iowa 14,147 3,062,309 216.5
Kansas 13,080 2,871,238 219.5
Kentucky 2,363 4,369,356 1849.1
Louisiana 7,977 4,574,836 573.5
Maine 7,270 1,328,188 182.7
Maryland 23,714 5,828,289 245.8
Massachusetts 12,941 6,587,536 509.0
Michigan 35,534 9,876,187 277.9
Minnesota 29,832 5,344,861 179.2
Mississippi 11,629 2,978,512 256.1
Missouri 34,004 6,010,688 176.8
Montana 4,240 998,199 235.4
Nebraska 13,692 1,842,641 134.6
Nevada 14,445 2,723,322 188.5
New Hampshire 4,571 1,318,194 288.4
New Jersey 24,313 8,821,155 362.8
New Mexico 9,741 2,082,224 213.8
New York 25,169 19,465,197 773.4
North Carolina 49,599 9,656,401 194.7
North Dakota 4,003 683,932 170.9
Ohio 19,088 11,544,951 604.8
Oklahoma 18,980 3,791,508 199.8
Oregon 17,015 3,871,859 227.6
Pennsylvania 53,319 12,742,886 239.0
Rhode Island 2,778 1,051,302 378.4
South Carolina 14,742 4,679,230 317.4
South Dakota 6,190 824,082 133.1
Tennessee 26,322 6,403,353 243.3
Texas 90,066 25,674,681 285.1
Utah 6,894 2,817,222 408.6
Vermont 2,647 626,431 236.7
Virginia 27,732 8,096,604 292.0
Washington 34,952 6,830,038 195.4
West Virginia 4,429 1,855,364 418.9
Wisconsin 40,549 5,711,767 140.9
Wyoming 7,159 568,158 79.4