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Technical review meeting on World Programme for the Census of Agriculture 2020 Volume 2 – Operational guidelines on implementing census of agriculture Rome, Italy 30-31 January 2017 Chapters 12 and13: Mapping & preparation of frames and Sample design Item 4 Oleg Cara Consultant, Agricultural Censuses and Surveys Team ESS FAO Naman Keita Consultant, Agricultural Censuses and Surveys Team ESS FAO 1 CONTENTS • • • • • • Mapping ◦ Purpose of maps used for Agricultural Census (AC) ◦ Cartographic work and types of maps Preparation of frames for AC ◦ Types of frames and sources of information ◦ Some guidelines on building frames ◦ Frame requirements for various census modalities Use of sampling for census enumeration Main types and choice of sample design Advantages & disadvantages of complete enumeration and sample enumeration censuses Discussion points 2 Purpose of maps Census planning and frame preparation o Provide the cartographic base for planning (including budget estimation of) the census. o For a sample enumeration can be used to improve sample design by providing information for stratification and other auxiliary information. Organization, conduct and supervision of field data collection o Maps (or sketches) are used to organize the field work. o GIS provides a computer-based design of EAs and significant automation of map production tasks. o The use of maps should be an essential part of the enumerators' training. Presentation and analysis of census results o Maps can be used to relate statistical data with the corresponding geographic area, facilitate the understanding of statistics and assure a more extended and appropriate use of data. 3 Cartographic work and types of maps • The cartographic work should be conducted during the early stages of preparatory census activities. • It should start with the inventory of available geospatial information and maps and the evaluation of their suitability for AC purposes. B • A large proportion of the cartographic preparations for an AC consists of delineating and identifying the enumerators' areas (EAs) of work. • In many countries EA maps are prepared as part of the cartographic work of the Population and Housing Census (PHC). In some countries the cartographic work is conducted for both PHC and AC (e.g. Brazil). • Adapting, revising and updating available maps to the census requirements. • Types of maps: topographic sheets, other government maps, satellite images, aerial photography, communication maps, land-use maps, economic maps, city and tourist maps, EA maps from PHC. 4 Types of frames • The List Frame is a list of agricultural holdings and/or households. However, when the list of agricultural holdings and/or households is missing, the list of EAs could serve as a starting point for the development of a census frame. • The Area Frame is a set of land elements, which may be either points or segments of land. • The Multiple Frame, in which part of the population is covered by a list frame (e.g. special holdings) and the remainder (e.g. other holdings) by an area frame. 5 Sources of information for the construction of an AC frame • • • • The statistical data and maps of the EAs of the most recent PHC and a list of EAs along with their number of households/housing units. The statistical data and maps of the EAs of the latest AC including a list of EAs with their number of holdings. Statistical farm registers, cadastral and other cartographic materials, other statistical and administrative data sources, which include listings of holdings and/or holders' addresses or their approximate location. It might be necessary, due to lack of reliable information, to prepare the census frame by conducting a listing operation (prior to starting the enumeration of the holdings). 6 Some guidelines on building frames for AC • To be able to enumerate all holdings a preliminary frame is indispensable. It is made of a set of physical materials (cartographic maps, EA maps, etc.). • When PHC does not include specific questions on agriculture, the economic activity status must be considered together with occupation and industry in order to provide an approximation for households involved in own-account agricultural production. • The minimum data items recommended to be included in the PHC to better identify such households are: (i) Whether the household is engaged in any form of own-account agriculture production (ii) measure of farm size, e.g. area of land & the number of livestock. • Use of farm registers & other statistical/administrative sources to build a frame. • Preparation of sampling frames corresponding to each sample selection stage, including detailed mapping to support the field data collection (when sampling is used). The frame requirement is directly related to the type of sampling. • Using new technology for building frames, e.g.: GPS, GIS, Remote Sensing. 7 Frame requirements for various census modalities (1) Frame requirement for a classical census o o o o o o An initial frame of holdings in the household sector and in the nonhousehold sector is needed. The total area of the country is unambiguously divided into nonoverlapping subdivisions - EAs in such a way so that the enumeration work in each area can be handled by a single enumerator during the census data collection period. Coordination of the construction of the EAs of the population and agricultural censuses. Use of available cartographic materials. It might be necessary (due to lack of good maps) to prepare sketches for the EAs. Conduct a listing operation due to lack of reliable information, if needed. Establish a sampling frame (when sampling is used). 8 Frame requirements for various census modalities (2) Frame requirement for a modular census o o o As for the classical census, an initial frame of holdings in the household sector (or EAs) and in the non-household sector is needed to conduct the complete enumeration for the core module (CM). The CM should provide the necessary information for building appropriate sampling frame(s) for the subsequent supplementary module(s), SM(s). A built-in process should be developed for generating sampling frame(s) for SM(s), according to the design(s) decided. Frame requirement for an integrated census and survey modality o o As for the classical census, an initial frame is needed for organizing the complete enumeration for the CM. The frame requirements for rotating modules are similar to those for SM of the modular census. Frame requirement: modality based on use of registers as a source of AC data o The frame requirements for field operation component are identical to those discussed in the modalities above. 9 Use of sampling for census enumeration • In a classical census sampling may be applied when: using the short-long questionnaire concept (the short questionnaire is administered to all target population of holdings, while the long questionnaire is administered only to a sample of such holdings); or conducting a sample-based census as a single one-off operation. • In the modular approach sampling is needed for selection of holdings to apply the supplementary module(s). • When the census is part of an integrated census/survey modality rotating modules are conducted on a sample basis. • Use of registers as a source of census data could also be combined with filed enumeration on a sample basis. 10 Sampling techniques Sampling techniques: simple random sampling (SRS), systematic sampling (SYS), stratified sampling (STR), sampling with probability proportional to size (PPS), multivariate probability proportional to size (MPPS), cluster sampling, etc. One-stage (element) sampling: a fairly complete and up-to-date frame is required. is not always feasible when conducting ACs, especially in countries with a not well established system of agricultural surveys. Cluster sampling: a sampling frame at the element level is not needed for the whole population. cost efficiency, that is, the relatively low cost per sample element. in practice, clusters tend to be internally homogeneous, and this intra-cluster homogeneity increases standard errors and thus decreases statistical efficiency. The multi-stage sampling procedure, which involves multiple sampling at different stages, aimed at achieving maximal accuracy of statistics for allowed costs, is largely employed for ACs and surveys. 11 Main types of sample designs for census enumeration • Sample designs can be classified according to the type of sampling frame used, i.e. based on: • • List frames Area frames and Multiple frames. The main difference between these types of sample designs is whether the final stage of sample selection is a listing of holdings or households, or is land based, or if a combination of a sample of area elements with a list sample is applied to obtain the census estimates. Handbook on Master Sampling Frames for Agricultural Statistics (Global Strategy, 2015). 12 List sample designs (1) • The most commonly used sampling procedures in ACs. • List sample designs often include some strata of “special holdings” that are completely enumerated, or have a high sampling fraction. List sample designs for classical censuses ◊ Element sampling (using SRS, SYS, STR, PPS, etc.). ◊ Single-stage cluster. ◊ Multi-stage sampling. ◊ Country examples: Croatia : One-stage sample design based on STR Suriname: Combination of complete enumeration with cluster sample design 13 List sample designs (2) List sample designs for modular census o o A multistage sampling for supplementary modules: Suits very well in-depth surveys when the application of detailed and time consuming questionnaires is needed. It is commonly applied, where EAs are the PSUs and holdings are the SSUs. Depending on the availability of information about PSUs, SSUs, etc., the use of STR or selection with PPS would be appropriate to improve the efficiency of the sample design. Country examples: Togo: two-stage sample design for supplementary modules Burkina Faso: two-stage probability sample design India: combination of one-stage and two-stage sampling designs. 14 Sample designs based on area frames and multiple frames Sample designs based on area frames o Well suited for estimating parameters related to land areas such as cropland and can be used to evaluate the quality of the data collection. o Has major limitations for estimating other parameters required by a census (such as on livestock, demographic and social characteristics, etc.): Many important agricultural characteristics have a skewed distribution; The sampling of area units alone increases the sampling variance. When land of a large holding belongs to a sampled segment, the expansion factor can lead to inaccurate estimators for some variables. For instance, farms that have livestock and do not have their own land are difficult to pick with an area frame. Sample designs based on multiple frames o The joint use of area and list frames: a list of relatively few “special holdings” complement the larger population of smaller farms covered by the area frame. o Country examples of agricultural censuses conducted in Fiji and Puerto Rico. 15 Choice of sample design • • • • • • Achieving maximal accuracy for available total budget (resources), or minimal costs for required accuracy/ level of aggregation for census data: two ways of stating the aims of efficiency. Resources include the availability of trained and experienced personnel in sampling techniques, financial and information resources. The sample design should be simple enough to operate in the field. List sample designs versus area sample designs. Multiple frame designs versus area sample designs. Multiple frame sample designs versus list sample designs (pros and cons determined by strengths and weaknesses of the area component of the former): Precision of the estimates. Basis for a crop yield estimation. Complexity of implementation. Mapping requirements. Proximity of the holder or respondent to the holding. Distinguishing characteristics. 16 Complete enumeration versus sample enumeration census Complete enumeration Advantages 1. 2. 3. 4. Reliable census results for the smallest administrative and geographic units and on rare events (such as crops/livestock types) Provides a reliable frame for the organization of subsequent regular infra-annual and annual sample surveys. In terms of frames, it is much less demanding in respect of the holdings’ characteristics Requires fewer highly qualified statistical personnel with expert knowledge of sampling methods than a census conducted on a sample basis.This is particularly important in countries with limited technical expertise Aggregating data from a complete enumeration is straightforward and does not involve statistical estimations. 1. 2. 3. 4. Sample enumeration Is generally less costly that a complete enumeration Contributes to decrease the overall response burden Requires a smaller number of enumerators and supervisors than a census conducted by complete enumeration. Consequently, the quality of data can be expected to be much better because of the employment of better trained enumerators and supervisors and better quality control Require less processing capacity and the results are usually available sooner. 17 Complete enumeration versus sample enumeration census Complete enumeration Sample enumeration Disadvantages 1. 2. 3. High cost and administrative complexity High overall response burden Requires a very large number of field staff. As a result: candidates with the desired qualifications might not be available in the required number the standard might be lowered adequate training of a large number of field census staff in a short period of time is also challenging, with a consequent effect on the quality of data 4. The amount of data to be processed is very large. The results may be considerably delayed if not sufficient data processing capacities are in place. 1. 2. 3. 4. 5. 6. The amount of subnational data and cross-tabulations that can be produced is limited Cannot provide accurate information on events that occur infrequently May not ensure an adequate or complete frame for subsequent agricultural surveys Requires a reliable sampling frame Requires personnel who are well trained in sampling methods and analysis Analyzing the data from a sample enumeration requires the use of more complicated techniques. 18 Discussion points • Relevance of: Sections on: mapping, frames, sample designs, advantages and disadvantages of complete enumeration and sample enumeration censuses. Boxes and country examples. 19 THANK YOU 20