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Department of Taxation and Finance

Survey of Ratio Study Methods Used By the States

(September 1995)


State Assessing
Units (a)
Frequency of Ratio Studies Use of Sales Use of Appraisals Data Period
(in Months)
Primary Measure of Assessment Level Uniformity Measures Reassessment Cycle (in Years)
Alabama County, 67 Annual Yes (b) No 6 (c) Median COD (d) 5
Arizona County, 15 Quarterly Yes (e) No 18-30 Median COD/COV (f) None
Arkansas County, 75 Annual Yes Yes 12 Weighted Mean (g) None None
Colorado County, 63 Annual Yes (b) Yes (h) 18 Median COD/PRD (i) 2
Connecticut Cities/Towns, 169 Annual Yes No 12 Median COD/PRD 10
Florida County, 67 Ann/Bien(j) Yes Yes (k) 12 Weighted Mean (g) COD 3 (visits
Georgia County, 159 Annual Yes Yes 12 Median/Wtd. Mean (l) COD/COV None
Idaho County, 44 Annual Yes (e) Rarely 12 Wtd. Mean/Median (m,g) COD/COV/PRD 5
Illinois County/Town, 969 Annual Yes (b) No 12 Median COE/Coefficient of Concentration 4
Iowa County, 111 Ann/Bien(n) Yes Yes (o) 12 Median (p) COD None
Kansas County, 105 Annual Yes (e) Yes (k) 12 (c) Median (g) COD/PRD (g) Annual Updates
Kentucky County, 120 Annual Yes Yes (k) 6 Median (g) COD 4
Louisiana Parish, 70 Annual(q) Yes Yes 12 Median COD 4
Maine City/Town/
Unincorporated areas, 488
Annual Yes Yes (r) 12 (c) Mean COD None
Massachusetts City/Town, 351 Bien/Trien (s) Yes (e, t) Yes (u) 12 (c) Median/Mean (v) COD 3
Michigan City/Town, 1527 Annual Yes (b) Yes (w) 24 Weighted Mean COD/PRD 5 (Voluntary)
Minnesota City/Town/Co., 2713 Annual Yes No 12/21 (x) Wtd. Mean/Median (y) COD/PRD 4
Mississippi County, 82 Annual Yes (e) No 12 Median COD/PRD None
Missouri County, 115 Biennial No Yes N/A Median (g) COD/PRD 2
Nebraska County, 93 Annual Yes (e) Yes (k) 18 Median COD/PRD (z) None
Nevada County, 17 Biennial No Yes N/A Median COD 5
New Hampshire City/Town, 259 Annual Yes No 12 Median COD/PRD None
New Jersey City/Town, 567 Annual Yes No 12 2-Yr. Wtd. Mean COD None
New Mexico County, 33 Annual Yes Rarely 12 Median COD/PRD 2
New York City/Town/Village/ County, 1241 Ann/Bien (aa) Yes (bb) Yes (cc) 12 (dd) Wtd. Mean/Median (ee) COD/PRD None
North Carolina County, 100 Annual Yes No 12 Median COD 8 (ff)
North Dakota City/Town, 1800 Annual Yes Yes (k, gg) 12 (c) Median COD/PRD None
Ohio County, 88 Triennial (hh) Yes (e) Rarely 36 Weighted Mean COD/PRD 6 (ii)
Oklahoma County, 77 Annual Yes Yes (k) 12 Median COD 4
Oregon County, 36 Annual Yes Rarely 12 (c) Mean/Median/Wtd. Mean (jj) COD/Av. Deviation 6
Pennsylvania County, 67 Annual Yes No 12 Mean None None
Rhode Island City/Town, 39 Annual Yes Yes 12 Median COD 10
South Carolina County, 46 Annual Yes Yes (k) 12 Median Index of Inequality 5
South Dakota County, 66 Annual Yes No 24 Median COD/PRD None
Tennessee County, 95 Variable (kk) Yes No 12 Median/Wtd. Mean (ll) COD/PRD 4 or 6
Texas County, 254 Annual Yes Yes 15 Weighted Mean (g) COD/PRD 3
Utah County, 29 Annual Yes Yes (mm) 18 Weighted Mean COD/COV/PRD 5 (nn)
Vermont City/Town, 251 Biennial Yes Yes (k) 24 Weighted Mean COD/PRD None
Virginia County/City, 135 Annual Yes No 12 Median None 2 city; 4 county
Washington County, 35 Annual Yes Rarely 8 Weighted Mean PRD 2, 4 or 6
West Virginia County, 55 Quarterly Yes No 12 Wtd. Mean & Median COD/PRD/M.W.(oo) 3
Wisconsin Co./Town/Vlg., 1849 Annual Yes Yes 12 Weighted Mean COD/PRD (pp) 5
Wyoming County, 23 Annual Yes No 12 Median COD/PRD 4


a. Units of local government which perform the assessing function.

b. Adjusted for financial terms.

c. Study period extended if valid sales are insufficient.

d. Coefficient of Dispersion.

e. Time adjusted.

f. Coefficient of Variation.

g. Uses confidence testing.

h. Agricultural class, and to supplement where sales are insufficient in other classes.

i. Price Related Differential (also known as the index of regressivity).

j. Annually tests whether each county is assessing within the permissible range of market value; biennially tests (half the counties per year) to determine the equitable distribution of state aid to schools.

k. To supplement where sales are insufficient.

l. The median is used by the Dept. of Revenue to test that the level of assessment meets statutory requirements. The weighted mean is calculated by the Audit Dept. to equalize values for school aid apportionment.

m. The weighted mean is calculated in one test to equalize values for school aid apportionment; the mean (or median) is calculated in a second test to adjust locally determined values, if necessary.

n. There are two purposes for the ratio studies done in Iowa. An annual test establishes equity among overlapping taxing districts and recipients of state aid. A biennial test equalizes all property classes in every assessing jurisdiction to the statutory level of 100% of true value.

o. Commercial and rural residential in biennial study.

p. A regression index is also calculated.

q. Selected property class studied in four-year period.

r. For residential and seasonal property only.

s. Biennial equalization study, triennial certification study.

t. Residential sales only

u. Audits in lieu of appraisals on non-residential property for triennial study; supplements with commercial/industrial appraisals for biennial study.

v. Uses median in triennial study; uses unweighted aggregate mean in biennial study.

w. Sporadic use of appraisals in commercial/industrial classes.

x. Twelve months for equalization purposes; 21 months for school aid purposes.

y. Uses weighted mean for state aid purposes; uses median for equalization purposes.

z. Both calculated only for residential property.

aa. Annual residential sales study, biennial equalization study.

bb. For residential sales study only.

cc. Used in equalization study only.

dd. Twelve months for residential ratio study; not applicable for equalization study.

ee. Uses weighted mean in equalization study; uses median in residential sales study.

ff. Some counties voluntarily revalue every four years.

gg. Appraisals are done by county directors.

hh. Semi-annual interim ratios issued.

ii. With updating in the third year of cycle.

jj. All three statistics are calculated by the state. Each county chooses which one is the best indicator for its array of ratios.

kk. Varies by each county's reappraisal cycle.

ll. Uses median for equalization purposes; uses weighted mean for update study purposes.

mm. Used for supplementing rural residential sales.

nn. With annual updates.

oo. Mann Whitney test.

pp. Also coefficient of concentration and frequency table.

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