University of Kentucky College of Agriculture
ENTFACT-113

PROCEDURE FOR SELECTING RANDOM LOCATIONS FOR SAMPLING

by Doug Johnson, Extension Entomologist
University of Kentucky College of Agriculture

 

These figures are designed to help you remove your personal bias while selecting sampling points in a field. You will have to modify them to fit larger and smaller fields.

 

  • 1. Divide the field into general sampling areas.
  • 2. Randomly select one number between 1 and 100 for each general sampling area.
  • 3. Consult Table 2. 100 Sets of Random Site Selection Directions, under ENTRY NUMBER, to find the random numbers you have selected. Record the set of walking instructions listed in the table for each of your random numbers.
  • 4. Select the first area of the field to be scouted.
  • 5. Go to the edge of that area. If this is a field edge go 30 paces into the field. This is your starting point.
  • 6. Use the walking instructions to locate your actual sample site.
  • 7. Take your sample.

 

As an example: let's look at a small corn field of 20 acres. According to the University of Kentucky IPM Scout Manual a field this size requires 3 samples to be taken.

 

  • 1. Divide the field into three general sampling areas.
  • 2. Select three random numbers say, 2, 31, 24.
  • 3. Look at Table 2 for Entry Numbers 2, 31, and 24 and you will find the following walking instructions:
Table 1: Example Site Selection
General Sampling Area
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
1
2
Right
3
19
2
31
Right
3
15
3
24
Left
9
1

  • 4. Select the first area to be scouted.
  • 5. Go to the edge of the first area. If it is a field edge go into the field 30 paces. From this starting point, follow the walking instructions for General Sampling Area 1 in the above table: Turn right, walk 3 paces, turn back to your original direction, take 19 paces, sample the area in front of you.
  • 6. Go to the next general sampling area and repeat the process using the second set of walking instructions (General Sampling Area 2 in the table above).

 

Through experience you will find that the number of paces specified may be too many or too few to use depending upon field size. If the field is very large, simply multiply the number of paces by 10 or 100. If the field is very small, divide the number of paces by some number (e.g. 10) to keep you from running over the end of a sampling area.

Remember the objective is to remove bias from your selection of sites. There is nothing magic about these numbers.

 

Table 2. 100 Sets of Random Site Selection Directions
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
1
Right
1
5
2
Right
3
19
3
Right
16
9
4
Right
17
24
5
Left
13
17
6
Right
5
6
7
Left
19
4
8
Left
11
18
9
Right
14
16
10
Right
7
20
11
Left
25
7
12
Right
24
14
13
Right
18
11
14
Right
6
21
15
Left
20
25
16
Right
15
1
17
Right
21
22
18
Left
23
23
19
Left
8
10
20
Right
2
2
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
21
Left
22
13
22
Right
16
8
23
Right
12
3
24
Left
9
12
25
Left
4
15
26
Right
2
6
27
Right
12
13
28
Left
11
22
29
Right
7
11
30
Right
4
14
31
Right
3
15
32
Right
21
3
33
Left
16
4
34
Right
19
17
35
Left
5
8
36
Right
6
19
37
Left
24
9
38
Right
23
5
39
Right
25
1
40
Right
15
23
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
41
Left
8
24
42
Left
10
25
43
Left
20
10
44
Right
22
16
45
Left
1
20
46
Right
9
7
47
Left
13
2
48
Left
18
12
49
Left
17
21
50
Right
14
18
51
Left
11
3
52
Right
6
19
53
Left
14
10
54
Left
22
22
55
Left
13
11
56
Left
3
12
57
Left
10
13
58
Right
18
21
59
Left
8
20
60
Left
2
15
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
61
Right
12
18
62
Left
4
8
63
Right
21
6
64
Right
15
24
65
Right
24
4
66
Left
5
13
67
Left
23
23
68
Left
7
14
69
Left
19
11
70
Left
25
1
71
Left
20
25
72
Right
1
12
73
Right
16
8
74
Left
17
7
75
Right
9
19
76
Left
10
24
77
Right
6
6
78
Left
7
15
79
Left
8
5
80
Left
17
21
Entry Number
Direction - Left or Right
Paces - Left or Right
Paces Away
81
Right
3
18
82
Right
18
17
83
Left
25
2
84
Left
20
16
85
Left
22
3
86
Right
23
22
87
Right
1
9
88
Left
16
10
89
Left
24
1
90
Right
14
23
91
Left
4
24
92
Left
2
25
93
Left
15
10
94
Left
19
16
95
Left
12
11
96
Right
11
23
97
Right
21
1
98
Right
9
4
99
Left
13
18
100
Left
5
21

 

Revised: 5/96

 

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

 

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!

 

Photos courtesy University of Kentucky Entomology