1. Alternative delimitations of area sampling frame
Workshop on Area Sampling Frame
Alternative delimitations of area sampling frame
Hassan Serghini
Budapest October 2012
This presentation is preparation by using references mentioned at the end of this presentation
NOM Prénom
Fonction

2. Segments with identifiable boundaries Square segments Point Sampling
27/04/2019
CONTENTS:
Introduction
Segments with identifiable boundaries
Square segments
Point Sampling
Strengths and weaknesses

3. Introduction
3 Types of segments are used for agricultural area sample surveys:
Segments with identifiable boundaries (roads, rivers, canals…) that provide an ambiguous identification of the segment;
Square segments, defined by straight lines forming square whose end points are established by map coordinates;
Segments based on random points: segment constructed around random point according to specific rules;

4. Segments with identifiable boundaries
The area sample design for segments that have identifiable permanent physical boundaries: segments with nearly equal size in each stratum;
The sampling usually consists of two-stage design;
Primary sampling units (PSU) also called counting units or frame units: areas with recognizable physical boundaries formed by segments;
The measure of PSU is equal to the number of segments it contains;

5. Segments with identifiable boundaries
PSUs in each stratum, are ordered by similarity of agricultural characteristics, ordering that will ensuring also a geographic distribution of the sample;
The PSUs facilitate the location of the sample of segments selected using systematic or random selection of segments;
For identifying a selected segment it is only necessary to partition the corresponding PSU into a number of segments equal to its assigned number of segments;
The frame of PSU allows to select the probability sample without actually listing all segments;
Random replicated sampling selection is generally used;

6. Square segments
After stratification a sample of square segments of equal size is selected;
The selection is simpler;
Data collection is the same as for segments with recognizable boundaries;
Difficulty for holders to recognize their land within the square segment;
Difficulty of obtaining reliable data for the tracts of a segment that are difficult to observe on the ground;

7. Point Sampling
Segment point: operator of land under the point; the sampling units the holding
Segment coincides with the land of agricultural holding and the segment boundaries are identified at the time of interview;
Obtain information about the entire farming operation;

8. Point Sampling
It is used when funds are not available for acquiring satellite images or areal photos (necessary for identifying boundaries),
Stratification as usual;
Data collection can be done by objective measurement of areas or simply by holders’ declarations;
Least cost compared to the others;

9. Point Sampling
Point may fall in non-farm areas (road, streams, property boundaries…): the first farm found to the north of the selected point is chosen in the sample;
If the point falls in the boundary of 2 farms: the farm to northeast became the sample unit;
Farms may have non contiguous parcels of land: all of them are in the fame sample;

10. Point Sampling
All information collected are based on holders declaration. With possible high non sampling errors.
Holders may not declare some of the parcels that are not contiguous;
Expand data using point-specific probabilities of selection based on total land area in stratum (S), number of points sampled in stratum (N), and total land operated by specific farmer (s):
The expansion factor (EF) for this farmer is: EF=S/N/s;
Ex. S=50000 ha, N=100; s=10 ha; EF=50;

11. Strengths and weaknesses
Types of segment
Strengths
Weaknesses
Segments with boundaries
Low non-sampling errors, tracts and farmers
High investment cost, necessity of boundaries
Squared Segments
Simpler sampling
Difficultly for farmers to recognize their lands within the segment
Point segments
Information for all the farm, no need for satellite images and areal photos
Non-sampling errors

12. References used
Earl E. Houseman, Area Frame Sampling in Agriculture, Statistical Reporting Service • U.S. Department of Agriculture, SRS No. 20;
FAO, Multiple Frame Agricultural Surveys, Volume 1, Current Surveys Based on Area Sampling Methods, FAO Statistical Development Series, FAO LIBRARY AN: , Rome 1996;
FAO, Multiple Frame Agricultural Surveys, Volume 2, Agricultural Survey Programmes Based on Area Frame or Dual Frame (Area and List) Sample Designs, FAO Statistical Development Series, FAO LIBRARY AN: , Rome 1998;

13.  شكرا
Thank you
Merci