HISTORIC NOTE
The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
of Florida
JUNE 1964
/j JUNE, 1964
AGRICULTURAL ECONOMICS MIMEO REPORT EC6413
A CONTINUING SURVEY FOR ESTIMATING
CURRENT NUMBERS OF FLORIDA
CITRUS TREES
ROY G. STOUT
J. W. TODD
THE DEPARTMENT OF AGRICULTURAL ECONOMICS, AGRICULTURAL EXPERIMENT STATION
in cooperation with
THE FLORIDA CROP AND LIVESTOCK REPORTING SERVICE, ORLANDO, FLORIDA
and THE DIVISION OF PLANT INDUSTRY, FLORIDA STATE DEPARTMENT OF AGRICULTURE, GAINESVILLE
CONTENTS
Page
INTRODUCTION . .. .. . ... 1
PROCEDURES ........ . . . 2
Sampling of Old Citrus Sections. . 3
Sampling of New Citrus .Sections e c .e 5
ESTIMATING TREE NUMBERS . . 6
Citrus Tree Numbers for 1961 .. ..... 6
Citrus Tree Numbers for 1962 .. . .. 7
Citrus Tree Numbers for 1963 . 9
Estimating Tree Numbers for rth Year ........ 12
STATISTICAL RELIABILITY OF ESTIMATES. . 13
Estimated Variances. .. 14
SOME REMARKS. .......... .. 18
SUMMARY ., c C . o o c e 0 .. 19
A CONTINUING SURVEY FOR ESTIMATING CURRENT NUMBERS
OF FLORIDA CITRUS TREES
Roy Go Stout* and Jo W0 Todd**
INTRODUCTION
During the three year period (195457) a complete enumeration was
made of the citrus trees in Florida, This tree census provided a more
complete breakdown of citrus tree numbers than had.ever been previously
available. These data.became extremely valuable to those who estimate
the size of the crop and for business leaders in the industry,, Today,
various business firms are requiring greater and greater accuracy in
current tree count .information, The Division of Plant Industry's job of
disease control and.inspection requires ever increasingaccuracy of tree
numbers and locations and.the .Crop and Livestock Reporting Service re
quires increased accuracy in tree.numbers for predicting the forthcoming
production as they rely more on objective methods of making estimates. l/
* Formerly Assistant Agricultural Economist, Florida Agricultural
Experiment Stationso
** Agricultural Statistician, Florida.Crop and Livestock Reporting
Service,
I/ Roy G, Stout, "Estimating Citrus Production by Use of the Frame Count
Survey" Journal.of Farm Economics, Volo XLIV, ppo 10371049o
Roy Go Stout, Size of Fruit and Droppage Rates.Influence Total Citrus
Production, Agricultural Economics Report 622, Florida Agricultural
Experiment Stations and Florida Crop and Livestock Reporting Service,
July, 1961i
B Wo Kelly, "Objective Methods for Forecasting Florida Citrus Pro
duction" Estadistica .Journal of the InterAmerican Statistical
Institute, .March, .19580
Since the completion of the enumeration of 1957, freezing weather,
removal of groves for industrial and residential development, .and the
movement of several million trees from nursery, indicates a need for
updating this .information, 2/ However, the cost of making a complete
enumeration of tree plantings and removals necessary to keep this census
up to date on an annual basis is prohibitive A system of continual
sampling has been.employed as .an.alternative .to complete enumeration,
The objectives of this paper are to: (1) describe the procedures
that are currently being used to.estimate tree numbers, and (2) estimate
the statistical reliability of the estimated tree numbers,
PROCEDURES
The current.sampling plan is designed so that 20 percent of all
citrus and potential citrus sections are covered each year This will
give complete coverage in five years Basically the sampling plan con
tains two component parts .in updating the 195457 census information0
One is a sampling of land .sections that .contained citrus in the 195457
census and the second component.is sampling all land sections considered
to be suitable for plantings but .contained no citrus in the last census
The first survey work.was .commenced.in 1960o Estimates of tree numbers
for 1961, 1962 and 1963 have been completed,
2/ Zach Savage, Movement of Citrus Trees from Florida Nurseries, July lI
1928 to June 30 19623 Agricultural Economics Mimeo Report 633,
Department of Agricultural Economics, Florida Agricultural Experiment
Stations, November, 1962o
Sampling of Old Citrus Sections
In preparing the basic sampling maps, every section showing commer
cial citrus in the 195457 census was numbered 1 through 5 in a serpentine
manner in each.countyo 3/ Each year 20 percent of these sections are
visited For example, the first year all sections.numbered five and the
second year all sections numbered two were visited, Records for all com
mercial groves from the 195457 census are used and every commercial grove
listed at that time is visited and a record is made regarding the present
existence or nonexistence of the grove
A rate of change in tree.numbers in all groves remaining that existed
in 1957 was made by recounting trees in a sample of approximately 550
of these remaining groves, This number changes slightly each year due to
rounding to whole numbers within counties, (It was 543 in 1961c) These
sample groves were completely enumerated and.the grove information matched
with 195457 information for the same groves to determine a rate of change
in numbers .and other related information A minimum of ten commercial
groves was included in the sample for each county providing there were
that many groves in the sample land sections The number of sample groves
in the larger citrus counties was determined by the ratio of the number of
groves in the county to.the total groves in those counties,
In these old citrus sections all.complete new groves planted since
the 195a57 census were completely enumerated,. The sample information
for old citrus sections is shown.in the first four columns of Table lo
3/ A commercial grove is all grove property that one .man or organization
owns in a given section,
Table loTotal and 1961 Sample Number of Sections and Groves
in Florida Citrus Survey by County
Old Citrus Sections
New Citrus
Sections
"Noncitrus"
Sections
Total No, of Total. No, of. Total No, of Total No, of
County Sec Sec, in Groves Groves in Sec Sect in Sec Sec, in
tions Sample in.Co. 161 Sample tions '61 Sample tions '61 Sample
Alachua
Brevard
Broward
Charlotte
Citrus
Clay
Collier
Dade
DeSoto
Duval
Flagler
Glades
Hardee
Hendry
Hernando
Highlands
Hillsboro
Ind, River
Lake
Lee
Manatee
Marion
Martin
Okeechobee
Orange
Osceola
Palm Beach
Pasco
Pinellas
Polk
Putnam
Sarasota
Seminole
Sto Johns
St, Lucie
Sumter
Volusia
Total
23 4
208 41
36 7
35 7
51 10
0 0
2 0
98 19
151 30
12 2
5 1
0 0
292 58
18 3
90 18
125 25
467 93
120 24
619 124
61 12
168 33
192 38
20 4
13 2
440 88
181 36
36 7
282 56
120 23
859 171
128 25
38 7
175 35
22 4
116 23
66 13
233 46
5502 1089
53
1027
196
63
110
0
4
545
613
63
6
0
1304
54
312
863
2332
757
4712
156
421
827
25
17
3568
533
42
1344
695
5242
509
108
958
54
674
105
1061
29353
10
10
10
10
9
0
0
123
10
9
1
0
13
3
9
9
24
10
47
9
9
10
6
4
37
10
8
14
9
53
9
10
9
10
10
9
10
543
25
65
16
22
70
45
2
86
47
0
28
16
194
12
88
89
136
40
142
20
99
64
37
25
44
144
54
111
ill
19
169
74
15
60
22
66
90
51
2287
5
12
3
4
14
9
0
17
9
0
5
3
38
3
17
17
27
8
27
4
19
12
7
5
8
48
10
22
4
33
14
3
12
4
13
18
10
464
317
539
364
157
370
0
450
210
480
0
92
477
144
200
203
761
369
253
155
776
487
615
486
683
434
946
389
359
82
989
311
473
96
406
384
632
14089
7
11
7
11
8
0
9
4
9
0
2
10
3
4
4
15
8
5
3
16
10
13
10
14
9
19
8
7
2
20
7
10
2
8
8
13
296
Sampling of New Citrus Sections
A complete listing was made of all sections that showed land suit
able for citrus, but did not contain citrus in the 195457 census, This
classification was made by use of aerial photographs, soil conservation
maps and consulting with various professional people in each county,
These sections were numbered from one to five in a serpentine manner in
each county and each year onefifth of these sections are covered and
all plantings .are completely enumerated,
Since this classification of land sections included subjective eval
uation, a check on the classification was made.by sampling the "noncitrus"
sections, A two percent sample of these "noncitrus" sections is checked
each year During the two years of operation, citrus has been found in
less than 10 of these "noncitrus" sections The last four columns of
Table 1 show the total and number of sample sections.for the new and
"noncitrus" components of the overall sampling plan,
Dade County, because of local problems, was handled differently.
This .county produces nearly all the state's Persian Limes and avocados
that are sold commercially, as well as a sizeable part of the lychees and
mangos Donna, the 1960 hurricane, struck through the center of this
area causing considerable damage, and it.was deemed necessary to enumer
ate completely all trees in the sample sections in this county,
As field work is completed by counties, all reports are edited and
punched on IBoM, cards. This information is then summarized and expand
ed to an estimate of the total trees.for each county,
6
ESTIMATING TREE NUMBERS
The following equations were used to expand the field data to esti=
mates of tree numbers by counties0
Citrus Tree Numbers for 1961
For tree numbers in old groves;
Y = X (1)
A o E i
T Xi
Where Y = 1961 estimate of number of trees for th county in old
groves
Yi = number of trees in ith sample grove in cth county in
1961o
xi = number of trees in ith sample grove in cth county in
1957o
X, = total number of trees in cth county in 1957o
For tree numbers in new grove plantings in old and new sections;
^ 1
Ycn Xj (2)
fn
A
Where Ycn = number of trees in new groves in cth county,
Xj = number.of trees in jth section
f = sampling rate = o2
So, Yen = 5 Xj (3)
For total trees by county;
A A A
Cc = Yo + Yn 4)
6
ESTIMATING TREE NUMBERS
The following equations were used to expand the field data to esti=
mates of tree numbers by counties0
Citrus Tree Numbers for 1961
For tree numbers in old groves;
Y = X (1)
A o E i
T Xi
Where Y = 1961 estimate of number of trees for th county in old
groves
Yi = number of trees in ith sample grove in cth county in
1961o
xi = number of trees in ith sample grove in cth county in
1957o
X, = total number of trees in cth county in 1957o
For tree numbers in new grove plantings in old and new sections;
^ 1
Ycn Xj (2)
fn
A
Where Ycn = number of trees in new groves in cth county,
Xj = number.of trees in jth section
f = sampling rate = o2
So, Yen = 5 Xj (3)
For total trees by county;
A A A
Cc = Yo + Yn 4)
A
Where Cc = total number of trees in cth county.
and for the state;
A
T = 'C (5)
Where T = estimated total number of trees in the state
Citrus Tree Numbers for 1962
The second 20 percent of the land sections and associated sample of
groves in these.sections were surveyed in 1962o Estimates of tree numbers
were derived for 1962 utilizing the data from both the 1961 and 1962 sam
ple data, In order to combine the two samples, the one year old trees
were removed from the 1962 sample and an estimate of the number of one
year old trees was made from the sample alone. Once the one year old
trees were removed from the 1962 sample it was the equivalent of a second
sample for 1961, hence, the two samples were combined for estimating coun
ty and state totals Then the estimated number of one year old trees was
added to give the final estimate for the 1962 season, Equation (1) was
extended as follows to estimate the number of trees in old groves in 1962
A Yil+ Eyi2 ,Pi2 Pi2
Y =  + Xc (6)
oxil xi2 C Xi2
Where Yco = 1962 estimate of number of trees for cth county,
yil = number of trees in ith sample grove in cth county in
1961.
Yi2 = number of trees in ith sample grove in cth county in
1962.
Pi2 = number of one year old trees in ith sample grove in cth
county in 1962o
il = number of trees in 1957 in the 1961 it sample grove in
cth county
xi2 = number of trees in 1957 in the 1962 ith sample grove in
cth county
Xc = number of trees in county in 1957,
The procedure for estimating the tree numbers in new grove
consists of extending equation (2).
Ycn = Xjl
1 ( Xj2 P ] + 
f2 ( 2 f2
plantings
LPj2 (7)
A
Where Y n= number of trees in new groves in cth county in 1962
Xjl = number of trees in jth sample section in 1961o
Xj2 = number of trees in jth sample section in 1962c
Pj2 = number of one year old trees in jth sample section in
1962
fl = sampling rate in 1961 = o20o f2 = sampling rate in
1962 = .,2
Since fl = f2, equation (7) becomes;
Ycn 2,5 [ Xjl + Z Xj2 Pj2j + 5 2Pj2
The total number of trees for each county and the state for 1962 was then
estimated as indicated in equations (4) and (5),
The total number of trees for all citrus, all orange, and all grape
fruit for 1961, 1962, and 1963 by counties as estimated by foregoing pro
cedures and for 1957 as reported from the complete census, are shown in
Tables 2 and 3. 4/
Citrus Tree Numbers for 1963
The freezes of December 1214, 1962 caused considerable damage to,
and killed outright, many citrus trees. Consequently, it was decided to
prepare estimates of tree numbers for 1963 based only on survey data con
ducted following the freeze. It was .alsofelt that the normal 20 percent
of sections and the approximately 550 groves would not be sufficient in
size due to greater variability between groves brought about by the
freeze,
4/ Some writers have indicated that the simple ratio estimates by strata
should not be used if the sample size is small, William Go Cochran,
Sampling Techniques, John Wiley and Sons, Inc,, New York, 1953,
pp .130313. Morris He Hansen, William No Hurwitz, William G, Madow,
Sample Survey Methods and Theory, Volo 1, John Wiley and Sons, Inc,,
1953, ppo 198200o One reason for this warning is that if there is a
bias in these small samples and the bias is accumulated over all
strata, there may be.a considerable error in the total0 Cochran says
that unless there is good empirical evidence to the contrary, a
combined ratio estimate is to be recommended. The combined ratio
estimate does not give ratio estimates for the strata (in this case,
the county), but only a total for the universe0. To compare these two
methods each county was expanded on a direct estimate for 1957 and
1961o These estimates were summed for the state and these totals
used to form the combined ratio estimate.for the state This com
bined ratio times 1957 tree numbers gave the 1961 estimate, The es
timate for all citrus trees for the state in groves that existed in
1957 by use of the stratified ratio estimate as described in this
report was 44,301,200 trees, The combined ratio procedure gave an
estimate of 44,321,300 total .citrus trees, a difference of 20,100
trees or about 005 percent0 The difference in the two procedures for
all oranges was lo6 percent and for all grapefruit it was 4ol percent
Table 2,Total Number of
Census in 1957,
Trees for All Citrus by Counties from Completed
and Estimated for 1961, 1962, and 1963
County
Alachua
Brevard
Broward
Charlotte
Citrus
Clay
Collier
Dade
DeSoto
Duval
Flagler
Glades
Hardee
Hendry
Hernando
Highlands
Hillsboro
Indian River
Lake
Lee
Manatee
Marion
Martin
Okeechobee
Orange
Osceola
Palm Beach
Pasco
Pinellas
Polk
Putnam
Sarasota
Seminole
Sto Johns
St, Lucie
Sumter
Volusia
Others
State
1957
1961
(Number of
42
1126
355
89
114
2
3
641
721
10
6
0
1483
45
572
1654
2458
1266
7825
177
653
1104
133
17
5197
884
114
2334
1041
8494
377
163
1116
29
1990
171
1080
43486
24
1345
285
84
132
2
354
676
5
7
2398
83
869
1986
3936
1442
8796
134
740
1407
326
24
4963
1222
110
2281
915
9383
412
145
1394
21
2207
247
964
49219
1962
Trees in Thousands)
31
1.511
305
107
146
3
62
327
858
6
12
28
2513
143
875
2016
3821
1731
9696
148
984
1131
573
40
4831
1354
122
2803
741
9453
385
135
1448
19
2545
255
998
52156
0 = less than 1,000
= no citrus,
a/ Included in Others for 1963e
1963
a/
1595
352
200
96
a/
155
346
1011
a/
76
2268
208
761
2007
3519
2182
7517
170
987
747
1276
110
4098
1095
165
1825
450
9241
306
164
1075
a/
3242
179
888
36
48348
Table 3,Total Number of Trees for All Orange and All Grapefruit by
Counties from Completed Census in 1957, and Estimated
for 1961,.1962, and 1963
County All.Orange All Grapefruit
1957 1961 1962 1963 1957 1961 1962 1963
(Number of Trees in .Thousands)
Alachua 38 22 28 a/ 2 1 2 a/
Brevard 736 893 1054 1134 305 360 345 319
Broward 295 209 243 292 46 66 50 48
Charlotte 49 44 92 179 9 6 4 7
Citrus 96 114 130 87 8 4 4 1
Clay 1 1 a/ 0 a/
Collier 2 1 62 150 1 
Dade 64 22 20 18 31 5 5 5
DeSoto 586 562 758 879 100 82 58 50
Duval 8 4 4 a/ a/
Flagler 5 5 10 a7 0 1/
Glades 0 28 76 0 0
Hardee 1356 2247 2353 2132 75 48 51 44
Hendry 35 78 131 195 7 2 7 8
Hernando 465 785 758 667 36 17 11 5
Highlands 1160 1635 1619 1568 312 158 183 197
Hillsboro 2006 3427 3331 3027 252 231 210 185
Indian River 431 525 687 1098 756 813 937 964
Lake 5816 6608 7338 5681 1106 1073 1037 772
Lee 106 94 102 124 45 19 25 22
Manatee 396 483 721 753 187 161 171 124
Marion 997 1344 1080 716 56 23 19 15
Martin 101 270 510 1056 10 12 38 33
Okeechobee 14 20 35 75 2 2 3 16
Orange 4232 4047 4014 3426 322 219 234 160
Osceola 740 1109 1222 984 56 41 47 49
Palm Beach 69 67 74 115 25 24 25 24
Pasco 1982 2002 2442 1563 203 126 155 124
Pinellas 477 448 401 279 495 405 295 142
Polk 5758 6983 7085 7092 1934 1566 1577 1462
Putnam 317 356 338 258 17 16 12 12
Sarasota 122 109 112 139 35 30 16 16
Seminole 888 1169 1252 883 83 71 47 45
Sto Johns 26 17 16 a/ 1 1 1 a/
St. Lucie 951 1190 1436 197'4 813 731 778 917
Sumter 154 236 235 156 5 6 6 3
Volusia 875 820 830 749 67 44 41 34
Others 29 1
State 31352 37944 40552 37554 7402 6363 6394 5799
0 = less than 1,000o = no citrus,
a/ Included in Others.for 1963o
In order to obtain a larger sample for estimating tree.numbers,
additional crews were employed and.the sample that was surveyed just
prior to the freeze in 1963 was resurveyed in 1963, In addition, the
sample that was normally scheduled for 1963 was also completed, Thus,
tree numbers for 1963 were based on an equivalent.two year sample using
formulas as described for estimating the tree numbers in 1962o Those
few counties that completely escaped freeze damage were not resurveyed,
Estimates for these counties .in 1963 were based on three years of survey
information,
During the first two years of the survey tree ages were assigned
according to size of bearing.surface, This procedure would create prob
lems in estimating tree numbers for 1964 and later years For example,
in 1964 the problem would arise in equations 6, 7, and.9 in distinguish
ing between the number of new plantings during the survey year and one
year old trees so classified.because of reduced bearing surface from
the freeze To adjust to this situation the actual age based on date of
planting was determined for each grove enumerated in addition to the
classification into age groups by size of bearing surface, In future
years the actual age grouping .will be used in estimating total tree num
bers and the age groups by size .of bearing surface will be used to allo
cate the total numbers into age groups
Estimating Tree Numbers for r'h Year
All information to the rth year can be utilized in preparing the
rth year estimate if the information .is adjusted for plantings between
the first and the rth year
Equation.(6) can be restated in.general terms as follows;
g r
o i=1 j=1 Yij
cor x c
g r
i Z xij
i=1 j=l
g r1
g rI
LE Z ij+l
i=1 j=l
A
Where Y = estimate of number of trees in old groves for cth
county in rth year.
yij = number of trees in ith grove for jth sample year,
xij = number of trees for ith grove for jth sample year that
were present in 1957,
Xc = number of trees in cth county in 1957o
Pi j+l= number of trees in young plantings in ith grove for
jth sample year of ages one to ro
(Note, The first sample contains.the trees that were one year old
in 1961, hence, Pi,j+l rather than Pij)c
Equation (7) can be written in general form as;
A1 k r k r
Ycnr rf Xij + ) (j1) Pij
r i=1 j=1 i=1 j=1
(10)
A
Where Y
Xij
Pij
= estimated number of trees of new plantings in cth
county for rth year,
= number of trees in ith section of jth year,
= number of trees in young plantings in ith grove for
jth sample year of agesone to ro
STATISTICAL RELIABILITY OF ESTIMATES
The systematic sampling procedure was used to select the sample sec
tions and groves because of the greater ease in selecting the samples
and maintaining the information in an orderly manner for such a large
and continuing sample The effect of the systematic sampling on the var
iance, in a few of the large counties, was found to be small0 Consequent
ly, the variances in this report were not adjusted for this effect Also
the computations on the ratio variances become complex if adjustments for
this sampling plan.are made Since simple random sampling procedures us
ually estimate larger variances than.systematic sampling and after study
ing the two estimates in two large citrus counties, it was decided that
the systematic sampling component could be ignored without significant
change in the results, recognizing that any bias would likely be on the
high side,
The following equations .were used to compute variance and sampling
errors for the county and state estimates,
Estimated Variances
For old groves;
co 2 2
s (Yco) = (f) yi + R xi 2Rc (11)
nco(ncol)
2 A
Where s (Y ) = the estimated variance of the estimate of total
trees in old groves in 1961 in the cth county,
Nco = total number of groves in cth county in 1957,
nco = sample number of groves in cth county for 1961,
Yi
Rc  for cth county,
xi
yi = number of trees in ith sample grove in cth county for
1961,
xi = number of trees in ith sample grove in cth county for
1957o
(l f) = finite correction factor, f = sampling rate,
Equation (11) is also appropriate in estimating the variance for 1962,
2 2
but nco, Y xi, and x ii are combined for both years after the one year
old trees are removed from each grove as indicated in equation (6),
For new groves;
2 2
2 2 co 2 s cn
s2(Y ) = M (1f) + M (lf)
cn co m c mcn
co on
(12)
2 A
Where s (Y ) = estimated variance of the estimate of total trees in
new groves in 1961 in cth county
M c= total number of old citrus sections in cth county in
1957o
mco= sample number of old citrus sections in cth county in
1961o
2
s = variance of the number of trees per section in old
c citrus sections for cth county in 1961,
Mcn mcn, and s2 have similar meaning for new citrus sections
cn c cn
in 19610
The estimated variance .for new groves in 1962 requires equation (12)
to be modified to include the estimated variance of the number of one
year old trees,
2 A
Where.s (Yn)
M = M
2
s and
col
2
s and
co2
2 2 2 2
2 col co2 2 cnc 2 (_13)
,) = M (1f) + M (lf)
O m the cntota
co m co J Ln mcn
estimated variance of the total number of trees in
new groves in c county in 1962o
Smc, and mcn are as defined in equation (12)o
2
cn estimated variance of the number of two year old
and older trees in old and new sections in
1962o
2
s = estimated variances for one year old trees in
cn2 old and new sections in 1962o
For total trees;
2 A 2 A 2 A
s (C) = s ( ) + s (Y ) (14)
c co cn
Where s (C) = estimated variance of the total trees in cth county
for each year of 1961 and 1962,
2 A 2 A
s(T) = s (C) (15)
c
2 A
Where s (T) = estimated variance of .the total trees in the state
for each year of 1961 and 1962,
Sampling Errors
The relative sampling error.for each county.was computed by:
soeo = t x 100
Cc
and for the state by;
tOCVs (T)
see = x 100
A
T
Where tI = the small sample normal deviate value at A05 level
The sampling .errors for the .state estimates indicate that the state
figures on.all citrus, all orange and.all grapefruit are reliable figures
(Table 4), The counties with the larger number of trees show the smallest
sampling errors. Lake County, with nearly nine million trees, had the
lowest sampling error of 6o0 percent, .followed by Polk County with ten
million trees and a sampling error of 803 percent in 1961,
The combined samples for making the 1962 estimates improved the reli
ability of most county estimates as well as increasing the precision of
Table 40Relative Sampling Errors of Estimated Total Number of All
Citrus, All Orange and
and State
All Citrus
1961 1962
(Percent)
All Grapefruit Trees,
of Florida by Years*
All Orange
1961 1962
(Percent)
by Counties
All Grapefruit
1961 1962
(Percent)
Alachua
Brevard
Broward
Charlotte
Citrus
Clay
Collier
Dade
DeSoto
Duval
Glades
Hardee
Hendry
Hernando
Highlands
Hillsboro
Indian River
Lake
Lee
Manatee
Marion
Martin
Okeechobee
Orange
Osceola
Palm Beach
Pasco
Pinellas
Polk
Putnam
Sarasota
Seminole
St, Johns
Sto Lucie
Sumter
Volusia
State
* CC = 005
County
22ol
13o8
57,5
905
10305
219o1
14o6
3800
24o5
14o1
15o5
12o7
6,0
2408
14o9
16o5
12,6
2062
15o8
14ol
25o7
8o3
15o6
1403
23,8
22o2
906
29o0
23o0
4,3
2200
22l1
20o9
3504
55o6
7202
7203
30o2
26o7
37,8
145,7
10,4
35o2
15ol
804
12.1
11.1
6,7
16o4
12o7
22o5
31,9
25.4
604
13o3
702
10,4
10o9
600
14o6
14o6
33ol
13o9
11o5
13,0
12,2
2,7
2303
21ol
5906
17o6
117 4
4708
12ol
3103
29o8
16o7
20o7
16,3
18,6
1804
14ol
19,6
2209
11,8
11,2
17,2
55,2
71ol
18ol
17o4
2704
22,7
18,0
35,5
26,9
409
2203
2602
21o2
4709
5800
81ol
7404
4602
29,1
25o5
145 7
9,3
3608
15o6
1001
16o9
17,4
9,7
25,6
17o5
3207
41ol
31o2
6,4
507
7,2
10o5
4309
806
14,7
18,4
38o8
15ol
14,0
13o3
2006
85,8
48,1
41,3
20o8
10o7
lo3
904
27,1
6,2
54,0
62,3
3,8
2602
20,0
13o6
53o2
10,5
87o8
34o6
16,8
71o4
4402
30o6
19,1
10o2
170,3
26,3
19o6
703
1004
20,3
4o6
83ol
77,5
7,2
22,9
28o0
3,7
31,6
17o6
7o6
2608
74o2
7,8
27,5
6,0
2202
4807
3o6
the state estimates Slightly over 50 percent of all citrus trees are
in counties with a sampling error of nine percent or less and 70 percent
in counties with a sampling error of 12 percent or less, By type, 37
percent of the orange and 56 percent of the grapefruit trees were in
counties with sampling errors of nine percent or less and 64 and 72 per
cent respectively in counties with sampling errors of 12 percent or less
Sampling errors for the 1963 estimated tree numbers were not com
putedo It is likely true that the freeze created greater variation in
estimated tree numbers, thereby, causing sampling errors in 1963 larger
than in 19620
SOME REMARKS
In conducting a continuous survey of this type, several problems
are encountered One problem, as indicated by the sampling error of
the counties with small number of trees, is having tree numbers that
may be smaller than the previous year, even though no layman type ex
planation is available This was not too serious a problem.in deriving
estimates for 1962 although it may be more of a problem in future years.
One way of handling this would be to publish data every other year, but
the industry is extremely interested in this information being released
on an annual basis The service aspects of such a report may justify
editing the figures to make the published figures remain in line, Large
groves and large new plantings, as are presently taking place in the
lower east coast counties, particularly Martin, will undoubtedly give
estimates in some years that will not be in line with the previous year's
estimate, In such cases an "educated" editing of the data.may be in
order
The amount of field work would, and sampling errors could., be re
duced somewhat if some more elaborate design were used in classifying
and sampling the potential citrus land sections, since trees are found
in only about 25 percent of the sections However, this visiting these
large numbers of sections with no trees does not effect the estimate of
the tree numbers and the present scheme fits the needs of the Division
of Plant Industry's disease.and pest control program and it reduces the
possibility of missing new sections containing citrus,
All field work is performed by employees of the Division of Plant
Industry, largely composed of five crews of two men each, traveling in
jeeps that maneuver in and out.of most groves0 Considerable information
on root stocks, diseases, spacings, .etc, is obtained in addition to the
tree numbers by age and variety The annual cost of the survey and tab
ulations is about $85,000, The complete census in 195457 cost about
onethird of a million dollars With increased wages and other costs,
such an undertaking would be considerably more today0 Therefore, con
sidering that the needs of the Division of Plant Industry are met as
well as obtaining data for a continuous updating of the number of citrus
trees, the costs of the present survey seem to be well justified,
SUMMARY
This report has discussed a procedure for updating tree numbers on
an annual basis from a date of complete enumeration and some statistical
analysis of the reliability of these estimates0 Estimates for the years
1961, 1962, and 1963 have been completed and field work for the 1964 sea
son is under wayo The analysis indicates that the estimated state numbers
20
are quite reliable and that the estimates in most counties are suffi
ciently accurate for many business.decisions and sampling procedures,
The reduction in the sampling errors as additional years are incorpor
ated into the estimates should increase the reliability of the tree
numbers beyond the level presented in this report,
