Concepts and Definitions Used in Area Sampling Frame Workshop on Area Sampling Frame Concepts and Definitions Used in Area Sampling Frame Hassan Serghini Budapest 15-18 October 2012 This presentation is preparation by using references mentioned at the end of this presentation NOM Prénom Fonction

Properties of sampling frames Target population Sampling units 17/01/2019 CONTENTS: Introduction Sampling frame Properties of sampling frames Target population Sampling units Reporting units Area sampling Types of segments Tracts Parcels and Fields Closed, open and weighted segments

Introduction Presentation of some concepts and definitions related to area sampling frame; All concepts used in other frames are applicable to area sampling frame

Sampling frame Sampling frame is a list of all sampling units and a set of rules for identifying population units; It is a means by which a target population may be sampled. Sampling frame is used for sampling and also for a census (Enumeration districts). List frame: farmers, agribusinesses, fields of crops; Area frame: segments of land; Multiple frame: combination of area frame with list frame designs

Properties of sampling frames Complete frame: all the target population (the universe) is covered by the frame; Frame coverage is an essential feature for its suitability for a survey; Inadequate coverage is a potential problem in agricultural surveys. The target population should be carefully defined: which segments of the population are excluded from coverage?

Properties of sampling frames Omissions and erroneous duplicates are often not known: unaware of the need to correct the frame before sampling. A few omissions or duplicates in a frame are acceptable; For completeness and accuracy, frame should be current. An obsolete frame obviously contains inaccuracies and is likely to be incomplete. Example of a frame that is out of date is an old agricultural census. It will not accurately reflect new farmers or those who quit agricultural activities.

Target population Target population: all the items (people, farms, animals, businesses,…) about which information is needed; The population actually sampled could be different from the target population. Example: estimation of a crop total production with omission of some regions where the production is very small. A survey population is the sampling frame and the procedures for using it. Difference between the survey population and a target population.

Sampling units Population units: individual elements of the target population; Sampling units: well-defined units that allow access to the target population; Sampling units are the units that a survey population is divided into for sampling purposes. They are the units subject to random selection.

Sampling units Cluster sampling is the sampling plans wherein the sampling units are groups (clusters) of reporting units. Primary Sampling Units (PSU) or Counting Units: areas with recognizable physical boundaries formed by a number of segments; The frame of PSUs allows to select the probability sample without listing all segments;

Reporting units Reporting units are the individual elements or units that compose a population for data collection (reporting) purposes. Each reporting unit in the population is associated with one and only one sampling unit. For area sampling the reporting unit is a tract or a farm (holding).

Area sampling Total area for the population is divided into segments. An area sampling unit is a "cluster" of reporting units associated with a segment. Area sampling is a form of cluster sampling and the theory of cluster sampling applies; A segment is a piece of land referring to the aggregate of the reporting unit that compose an area sampling unit; Segment is also used to mean area sampling

Types of segments Segment with identifiable physical boundaries (roads, railroads, rivers, canal, tracks…); Square segment: defined by straight lines forming squares; its end points established by latitude and longitude coordinates (associate farms, land, animals, etc. with land inside the segment); Point segment: segment constructed around a random point with specific rules associating farms, land, animals, etc. with land inside or touching the segment;

Tracts Each segment is divided into non-overlapping tracts. A tract is a the part of the holding which lies within the boundaries of the segment, or the land of the segment not part of any agricultural holding; Two elements in the definition of a tract: The definition of a farm and by The boundaries of a segment. A farm is composed of one or more tracts.

Parcels and Fields A tract is divided into a number of parcels; A parcel is a piece of land entirely surrounded by other land, water, road… not forming part of the holding; A parcel consist of 1 or more fields adjacent to each other; A field is a piece of land on which a specific variety of crop and planting date or specific crop mixture

Closed, open and weighted segments B G C D F Segment limits, Tract limits, Farmer residence

Closed, open and weighted segments Tract Farm Description A 1 An entire farm, operator lives inside the segment. B 2 An entire farm, operator does not live inside the segment. C 3 A nonfarm tract. One resident who operate a farm. No part of their farm is located in this segment. D 4 Tract D is composed of 2 parcels at two locations within the segment. Farmer lives in the segment and has no land outside the Segment E 5 Tracts E and E' compose farm number 5. A segment boundary is dividing the farm into two tracts. The operator lives in tract E’ F 6 A part of farm number 6. The remainder of the farm is a tract located a few miles away from this segment. The operator lives outside the segment. G 7 Tract G is part of farm number 7. The operator lives In the segment

Closed, open and weighted segments Closed segments: tracts A, B, C, D (2 parcels), E, F and G; Open segments: Farms 1, 3 and 4; Weighted segment: Farms 1 (weight=1), 2 (weight=1), 3 (weight=0), 4 (weight=1), 5 (weight=E/(E+E’)), 6 (weight=F/(F+ Reminder of the farm)), 7 (weight=G/(G+ Reminder of the farm)),

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: 375713, 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: 401697, Rome 1998;

 شكرا Thank you Merci