FAO STATISTICAL DEVELOPMENT SERIES No. 6
CONDUCTING AGRICULTURAL CENSUSES AND SURVEYS
Food and Agriculture Organization of the United Nations
Rome, 1995

CENSUS ENUMERATION

Census enumeration is a key census phase and the success of the census depends on it being done quickly, efficiently and with proven methods. This chapter describes different methods which can be applied in agricultural censuses and surveys, such as sampling (see also Chapter 7), interviewing, etc. The period and duration of enumeration is also discussed. There are also references to specific problems, such as mixed cropping, continuous harvesting, shifting cultivation and nomadic livestock. Detailed instructions are given on how to approach holders in order to gain their confidence, collaboration and cooperation. 

Particularly relevant are the following related topics: Instruction Manuals (Chapter 11), Training Programme (Chapter 12) and Organization of the Field Work (Chapter 15).

Introduction

14.1 The agricultural census operation consists of a series of closely-related activities which must be carefully planned in advance. It requires a well-coordinated organization from the planning stage to the dissemination stage. This operation must be able to handle the problems of statistical measurement of various characteristics of the agricultural holding, which is the unit of enumeration, and is generally considered to be much more complex than in other types of censuses and surveys. The agricultural census attempts to survey the entire agricultural economy of a country; therefore, the operation is particularly difficult for developing countries which have limited experience in organizing censuses and surveys. The census, as the name implies, is a collection of data for all individual agricultural holdings by direct enumeration. The economy of most developing countries is based on agriculture. These countries want to develop their agriculture rapidly using modern agricultural technology mostly generated in developed countries. To do so, requires detailed data on various characteristics of agricultural holdings.

14.2 Resource constraints are a major factor as each country considers whether the agricultural census is to be conducted as a complete enumeration or on a sample basis. Both methods have advantages and disadvantages. A census on the basis of a complete enumeration presupposes the existence of a certain minimum of facilities, such as funds, professional personnel for planning census methodology, sufficient number of qualified enumerators and supervisors, mapping material for the entire area to be covered by the census, data processing equipment, etc. All of these resources are not always available, especially in developing countries, with the result that a census on the basis of a compete enumeration cannot be conducted. However, a sample enumeration, even though it requires basically the same type of resources, requires fewer of them since the size of the operation can be much smaller. When making the decision to conduct a sample or a complete enumeration census, the advantages and disadvantages of both methods should be very carefully considered.

14.3 The application of sampling methods in an agricultural census and its advantages and disadvantages are discussed in Chapter 7. In this respect there are three main types of censuses to be considered:

1. Complete enumeration implies collection of data from all agricultural holdings. This is traditional, usually preferable, but is the most expensive method.
2. Sample enumeration implies drawing a "representative" sample of holdings and collecting data from only these holdings. This method should be used when resources are limited and when using objective measurement techniques.
3. A combination of complete and sample enumeration can be done in many different ways, such as the complete enumeration of large holdings and a sample enumeration of small holdings, or the collection of limited data by interview from all holdings and using sampling for area measurement, or for agricultural inputs, fertilizers, pesticides, machinery, etc.

14.4 The items of investigation which usually refer to the whole year are: economic activities and production of the holding, employment in agriculture, aggregate area under crops, area of land irrigated, agricultural machines used on the holding, use of fertilizers and soil dressing, existence of wood and fishery production, etc. A different time reference may be used for some items, such as a week or a month for employment in agriculture.

14.5 Questions related to a specific date generally refer to information regarding the holding, holder, and tenure of holding; land utilization, number of trees or vines; number of livestock and poultry; demographic classification; number of permanent workers; area of land provided with irrigation facilities and drainage; stationary power-producing machinery, etc. When the area under crops refers to "on the date of enumeration" the time reference is a specific date. Some countries record some livestock products, such as milk, cheese, etc., with a time reference on a specific date. The specific date is usually considered the day of enumeration. In many countries there is more than one crop season during the year. Usually, one of these seasons is the major season. In such cases, the information on total area of holding, area under different forms of tenure, and area classified according to utilization should relate to a specific date in the major crop season. If the seasons are equally important then information on these items may relate to a specific date during the season nearest to the date of enumeration.

Duration and period of enumeration

14.6 Duration of enumeration refers to the time taken to conduct the census enumeration. In the case of a population census de facto, the entire operation is ideally completed in one day, at least in urban areas, and in just a few days in rural areas. This is not possible in the case of an agricultural census. Generally, the enumeration is spread over a longer period. The duration of enumeration depends on many factors, such as availability of qualified personnel to serve as enumerators, length of questionnaires, use of objective measurements, means of communication, climatic conditions, etc. There may be certain items of information in the census programme dealing with data which can be more reliable if collected in more than one round of surveys. Data on employment in agriculture usually relate to the week preceding the date of enumeration, i.e., the period of one week which ends on the day of enumeration. This information if collected only once will have limited value. On the other hand, if the question is asked about employment over the census year the information may seriously be affected by respondent memory lapse. The same is true of livestock products such as milk and cheese, especially for small producers who maintain no records. For such items of information the countries may prefer to collect data by means of successive sample surveys at different times during the agricultural year.

14.7 Generally, countries with well developed agricultural statistics include in the agricultural census only those items on which data can be collected in one visit for the whole year. Data requiring repeated visits such as employment, production, etc., are collected by specialized surveys. The period of enumeration for censuses of agriculture organized by different countries has varied from about a week to more than a year in case of repeat visits. Countries organizing only one enumeration round tend to complete the field work in one to two months. It is advisable to complete the enumeration in as short a period as possible.

14.8 The enumeration period refers to the specific time of year when census enumeration operations are under way. This time frame can greatly affect the accuracy of census results. It is desirable that the interval between the enumeration period and the reference date should be kept to a minimum to avoid memory lapses. In countries where data on harvested crop areas are collected by interview, and data on crop production are also collected, enumeration should be immediately after the harvest of principal crops when the holder can be expected to have the information readily available and more free time for the enumerator.

14.9 In countries with more than one cropping season, more than one visit is desirable, particularly if crop area is to be measured. Field area measurements for a season can be carried out soon after the sowing is completed, and the crop yield surveys can start as soon as the crop harvest begins. Generally, not more than two crop seasons are realized in most countries. The second phase, i.e., the crop yield survey of the first season, will then coincide with the field area measurements of the second season and the crop yield survey of the second season will be the third phase.

14.10 Data on livestock production are normally collected in specialized surveys by interviewing the holders on volume of livestock products, such as milk yield, which varies from season to season, and production of wool and mohair which are produced almost entirely within fixed shearing seasons. To minimize errors arising from memory lapses, information on such items should be obtained soon after completion of a season. For milk yield information, a visit to the holdings at the close of each quarter of the year will be desirable. One or two of the quarters can be made to coincide with the sheep and goat shearing seasons. These quarters can also coincide with the three phases of land use and crop area and yield surveys. Thus, enumeration aimed at collecting all these data can be divided into four phases. In each phase the data on employment characteristics can be collected for the previous quarter to measure seasonal labour input variability.

14.11 The agricultural calendar giving inter alia the sowing and harvesting seasons and peak periods of sale of crop production, and the production periods of the other agricultural products, is indispensable in determining the phases of the agricultural census and survey periods of different items in a particular phase. In many countries the agricultural calendar dominates the census planning and organization (e.g., some areas may not be accessible in the rainy season). Data collected on annual agricultural production surveys, farm management surveys and from extension services can be used to prepare an agricultural calendar. These calendars can also be used to control census operations (and to plan annual agricultural surveys) and their preparation should therefore receive priority.

14.12 It is important that the enumerators select a suitable time to interview the holders. During the day the holders are usually at work. Therefore, mornings or evenings are suggested as more suitable for interviewing. The enumerators cannot work only during fixed hours each day. They cannot necessarily choose Sundays as holidays. In many countries there are certain "market" days on which most of the holders go to the market place to make their sales and purchases and cannot be contacted at home. It is advisable that on such days the enumerators observe their days of rest. Such arrangements have to be in line with local situations. In some countries there are some provinces or areas which are inaccessible during certain times of the year due to snow or floods, etc. The timing for enumerating these areas should be given priority over other areas.

Control of census operations and time schedule

14.13 In a country-wide operation like the agricultural census where staff are spread all over the country with a tight time schedule, it is of prime importance to devise ways and means for day-to-day control of operations so they are planned, organized and carried out methodically, correctly and according to a pre-determined time schedule. The need for an adequate number of supervisors and detailed guidelines for them and their training is discussed in Chapter 11. Designing a control chart for each phase or round of the census and a time schedule for enumerators and supervisors is most important.

14.14 For each phase of the census, a control chart giving the estimated date of commencement of an operation on any census item and the estimated period for its completion can be developed. The experience and knowledge gained in past censuses, and even in exploratory and pilot censuses, can be used to design and formulate the control chart. Against this control chart, the performance of each enumerator can be assessed.

14.15 In order for the control chart to be really effective, at the end of each day's work each enumerator should be required to record on a prescribed time-disposition schedule the work completed (see example in Frame 14.1). The content of this schedule can differ from country to country, phase to phase and month to month in the same phase, depending on the items of work to be covered in a phase or a month.

Country....................................... Province...................................... To be completed each day by the enumerator for the month of ............. Date  Morning=M  Afternoon=A  Village where the enumerator worked  Name of enumerated holder(s)  Nº of completed quest.  Nº of measured parcels  Yields measured ( crop and Nº of parcel )  OBSERVATIONS  1  2  3  4  5  6  7  8

Methods of enumeration

14.16 The mail method of collecting data for a census is generally used in countries where the holders are educated and maintain accurate accounts of holding operations. However, data suffer from errors arising from non-response and biases inherent in a mail questionnaire method. Mail questionnaires can be used in a census of large modern holdings, settlements and irrigation schemes, and holdings under the control, supervision, guidance or management of government or public organizations and institutions for which records are maintained or can be maintained. For individual agricultural holdings, which are mostly small and subsistence in character, the census will have to be conducted by interview or inquiry method with the help of trained enumerators.

14.17 While actual measurements are desired and possible in respect of items such as land use, and crop areas and yields, information on items such as livestock numbers (and even livestock products if included under the census programme), machinery and equipment, holding population and employment, etc., will have to be collected by interviewing the holders. It is useful (if possible) to make provision for physical verification of part of the information obtained by interview. This can be done at all three stages, namely by the enumerators themselves in the process of enumeration, by supervisors in a programme of post-enumeration verification. Systems of adequate cross-checks of information on related items at the inquiry stage can be developed. This will not only improve the quality of the data, but will also give the enumerators an insight into the types of mistakes respondents are likely to make and the precautions to be taken to avoid them.

14.18 Objective methods of area and yield measurements and physical verification can be applied where the census is conducted by trained enumerators. In the case of census by mail questionnaire, the respondents are expected to know the crop areas and production, and will frame their own estimates in which they can use measurements already taken, if any, of sales, ratios of quantity of seed planted to area planted, estimated average yield per unit, fertilizer and pesticide application rates, etc. They can also use the method of measuring field dimensions by pacing. Measurements by local weights and measures can be used to estimate production of commodities such as milk, wool and mohair.

14.19 Objective measurement of areas can be done in different ways: (i) by actual measurements in the field or (ii) by using aerial photography or remote sensing imagery. There are different methods of actual field measurement such as rectangulation, triangulation and compass traversing. Rectangulation is recommended as the simplest if most of the fields are rectangular. Triangulation is a more universal method than rectangulation but requires walking inside the field. Compass traversing consists of measuring the length of the sides of a field and taking compass bearings. This is the most universal method, recommended by FAO, with the advantage of self-control through so-called closure error. This method requires the following equipment: measuring tape 20-50 metres, compass with ½ degree precision, sometimes a clinometer for measuring slopes in mountainous areas and a programmable calculator to calculate the area (usually for use by supervisors). Whatever method is applied, actual field measurements are very time-consuming because each field has to be visited by the enumerators. For this reason measurements are done only on a sampling basis and never by complete enumeration.

14.20 Objective yield measurements are even more time-consuming and require a visit to the field at the time of the harvest.

14.21 The use of aerial photography for measuring areas of fields, although feasible, has a very limited application in agricultural censuses and surveys. Agricultural census data are collected from agricultural holdings and the use of aerial photographs implies that each field of a holding covered by the census is identified by the enumerator and the holder on available photos. Aerial photographs are costly and create organizational complications to ensure that up-to-date photos are available at the time of the enumerator's visit. There may be distortions in size of fields on a photo due to difficulties in keeping horizontal flight at a constant altitude and due to uneven terrain. Use of remote sensing data for estimating field area is only possible for very large fields (such as those in the central parts of U.S.A. and Canada) but even then it is not normally used because of high costs.

14.22 The use of satellite data in the U.S.A. to improve sample estimates for crop areas is an important application of remote sensing. Considerable improvement has been achieved for some crops and, as a result, the sample size using satellite data could be cut by half to achieve the same precision. A new generation of satellites which produce better imagery are expected to increase the applicability of remote sensing in crop estimation work.

14.23 It should be mentioned that remote sensing has proved to be very useful for agricultural statistics for broad land use classification and particularly for construction of area sampling frames. Area sampling frames constructed using satellite imagery are considered to be superior to classical frames (list of villages) as they guarantee better coverage (fewer omissions and duplications) and do not require frequent updating. Although the area sampling frame is not important for complete enumeration censuses, it can be for sample surveys and is considered to be one of the most important applications of remote sensing in agricultural statistics. This subject is discussed in more detail in Chapters 5 and 6.

14.24 There are several important aspects of using remote sensing in land use statistics:

1. Remote sensing has the advantage over agricultural censuses and surveys as it covers all land territory while agricultural surveys cover only the area of the agricultural holding, which in some countries may exclude communal pastures, forests, etc.
2. Remote sensing can provide data on broad land-use categories, such as cultivated land, pastures, forests, water areas, etc. Further breakdown of land use into crop types or other smaller categories of land use has not been successful.
3. Data on broad land-use categories, when combined with an area sampling frame, are very useful to prepare an efficient sampling design for agricultural sample surveys.
4. There are some conceptual problems of comparability of data on agricultural land use, as remote sensing relies on completely objective methods (biomass, etc.), while agricultural censuses and surveys use holders' concepts (forest grazing land is classified as forest or pastures according to its main use). Classification of remote sensing data requires "ground truth" which can be obtained from agricultural censuses or surveys.
5. Remote sensing is an independent source of land-use data which does not use the agricultural holding as a unit of enumeration and, apart from the consideration mentioned earlier, this application of remote sensing is not described in this publication.

14.26 In the interview method there are various techniques used to obtain reliable data. To get the right answer to a question often a number of indirect questions will have to be used by the interviewers. They may also have to give background explanations in the dialect in which they are interviewing the respondent in order to communicate the proper meaning of the original questions. Enumerators should be encouraged to note the data and other information that they secure through conversation with the respondent so that they can summarize this material in the form of explicit answers on the main questionnaire. Instead of a separate notebook, space may be provided on the questionnaire itself, e.g., on the back of the sheets, to record the data from which the final answer to each specified question in the questionnaire is to be built. Ascertaining the area of an agricultural holding will illustrate this point. The respondent is hardly expected to understand the definition of a holding. The enumerators can obtain from the respondents all land which is connected in one capacity or another, irrespective of its location in the village or locality in which they reside, or in any other area and then adjust all land which they may own but do not use themselves, as rented to someone else, including land which they may have rented from someone and again sub-let out to someone. The enumerators may have to interpose a suitable statement reassuring the respondent of the confidential nature of the information they have reported and that it is intended to provide correct data on land use, cropping patterns, tenancy systems, etc. Obviously, in the interview, the responsibility of obtaining accurate information lies with the enumerators. For this reason enumerators have to be thoroughly trained on concepts. They are also given tips to use in the interview methodology. In addition, a detailed instruction manual is supplied to each enumerator to be consulted when needed. The contents of the instruction manual was described in Chapter 11.

14.27 Enumerators are normally expected to enter "zero" answers in the questionnaire. This is very important in order to make sure that they did not forget to ask a question. In "Introductory questions" such as "Any livestock?" (see Chapter 8), interviewers would skip all detailed questions for holdings with no livestock.

Some tips on interviewing

14.28 The interview method of data collection is normally the main method used by census enumerators. In addition to the details above, much has already been said in Chapter 11 Instruction manuals and Chapter 12 Training programme about this method. Some organizational aspects will be described in Chapter 15 Organization of field work. This Section includes practical advice on interviewing respondents.

14.29 The enumerator should establish a relationship of confidence. The first step is often the most difficult for the enumerator because during the initial contact the respondent needs to be motivated to permit the interview. The ideal atmosphere for such motivation is one of mutual confidence. It must also be based on a genuine and deeply-felt respect on the part of each participant for the other person. It is the enumerator's responsibility to take the lead in establishing a relationship of mutual confidence.

14.30 Ordinarily the enumerator would proceed as follows:

1. Identify himself by showing an official identification card.
2. Explain the purpose and objectives of the census.
3. Describe the method by which the respondent was selected, if sampling is used.
4. State the confidential nature of the interview as provided by the census law.

14.31 The enumerator should help the respondents feel at ease and ready to talk. To achieve this, the enumerators should also be at ease. They can demonstrate to the respondents their confidence by using an informal and natural (conversational) manner of speaking. They should begin with a conversation on items of mutual interest, such as the ball game or the weather. They should carry on such a conversation to allow the respondents a little time to get accustomed to the situation. However, this conversation should not be prolonged as it may suggest to the respondents that the interviewers are reluctant to deal with the real purpose of the interview, and the respondents' time is valuable.

14.32 Good interviewing means asking the questions properly and recording the answers accurately. The enumerators are expected to ask all applicable questions, to ask them in the order presented and to make no unauthorized variations in the wording. The asking of questions if different will affect the way they are answered. The enumerator should be aware of this and be instructed to adhere to the prescribed wording.

14.33 It is essential that the respondent feels free to talk without unnecessary interruptions. Once the interview is proceeding, the respondent should be allowed to talk freely with little prodding from the enumerator. The enumerator should not dominate the interview nor make unnecessary remarks. The interview must be in a warm and cordial atmosphere.

14.34 One of the most important qualities the enumerator should develop is to listen. Listening is a skill which must be learned and practised. Only through proper listening can the enumerator discriminate between what should and should not be recorded.

14.35 Enough time should be allocated for the interview. The time to be allocated for the interview should be sufficient for the respondents to ponder their answers. The respondents should not feel that they are being pressed to complete the interview in a very short time. The enumerator should not cut the interview short because they are under pressure to complete the census of an area in a short period or the interview will be hasty and the respondents may not give complete answers.

14.36 The enumerator should control the interview. Quite often respondents will avoid certain questions by trying to direct the discussion to other topics in the course of the interview. Some questions are necessary and unavoidable on the census questionnaires. The respondents may become tired of responding and need re-stimulation. On other occasions, they may be engaging in irrelevant accounts of how they happened to use a particular rice variety. Raising a well-timed question will put the interview on its proper course.

14.37 Responses should be recorded during the interview. Experience has shown that the only accurate way to reproduce the responses is to record them during the time of the interview. Relevant information will most certainly be lost if recording is left until the interview has been completed.

Special problems of census enumeration

14.38 Crops cultivated simultaneously: This is one of the most difficult problems in agricultural statistics in African countries. Similar to kitchen gardens mentioned above, this refers to two or more different temporary or permanent crops grown simultaneously in the same field or plot. Mixtures of temporary and permanent crops are called crops grown in association with each other. Problems come from the difficulties in allocating area to each constituent crop and estimating production for each crop.

14.39 There are a few cases of crops being cultivated simultaneously which do not represent a major problem. These are some traditional combinations of temporary crops grown and harvested as a mixture in certain countries (e.g., millet and sorghum, mixed grasses grown for hay, etc.). It is best to treat a mixture of this kind as a single crop without attempting to estimate area under each crop. Regarding crops cultivated simultaneously which are harvested separately, there are countries with just a few typical mixtures (e.g., maize and beans) grown in rows. Such mixtures may be shown as a separate crop, and when grown in rows it may be relatively easy to estimate the area under each constituent crop.

14.40 Problems refer to situations when many crops grow together in thousands of different combinations. In such cases the census questionnaire allows space for two to six constituent crops (depending on the country). Experience has shown that at least four of the most important crops should be considered. Some important commercial crops, such as chili can be omitted as not being the most important crops in the field.

14.41 A relatively simple way of handling this situation is to classify each crop as a pure stand, principal (predominant, main) crop in a mixture, or as a secondary. In this way, total cultivated land can be calculated as the sum of pure stand and principal crops, without duplication. Production can be estimated if yields are known for each of the three crop classes.

14.42 Most countries with problems related to simultaneous crop cultivation use some kind of objective method to allocate a part of the field area to each constituent crop. The so-called imputed (theoretical) area is calculated as the equivalent of the pure stand area by using the density of plants or some other criteria (amount of seed, estimated production, etc.). The sum of imputed area may be larger than the physical area of the field indicating a beneficial interaction between constituent crops. The allocated area is calculated by adjusting the imputed area proportionately, so that the sum of allocated area is equal to the physical area of the field.

14.43 In the presentation and/or tabulation of these crop areas, it would be very useful to present the following four types of area separately for each particular crop:

1. Total area of the crop in pure stand.
2. Total area of the crop cultivated with others.
3. Total imputed area of the crop.
4. Total allocated area of the crop.

14.44 For associated crops, the area should be recorded both under the fruit tree (orchard) crop and the ground cultivated crop and it should be specified whether fruit trees are of a bearing or a non-bearing age.

14.45 Continuous harvesting: Root crops such as carrots, beetroots, radishes, turnips, sweet potatoes, green corn cobs, etc., can be harvested continuously from the same field throughout the season. In the case of green beans and green peas, and leafy vegetables such as spinach, continuous harvesting takes place through the season from the same plants. To these can be added cotton, where several pickings are made from the same plants. These are annual field crops which are ploughed up and destroyed at the end of the season. The perennial fruit trees and long duration crops (i.e., sugar cane standing in the field for more than one agricultural year) are also harvested continuously during the season.

14.46 The area of these crops has to be enumerated only once during an agricultural year irrespective of the number of harvestings from the same fields or plants. Estimations of their yield rates for all harvestings during the year have to be included. If crop-cutting surveys are designed to estimate their yield rates (which would be difficult as part of census operations), all the harvestings in sample plots will have to be taken. Perhaps regression equations could be worked out between the yield obtained from the first few harvestings and the total yield.

14.47 In some cases, the continuous harvestings might extend into a succeeding agricultural year. If such extended harvestings cover only a small part of the succeeding year, it will be more practical to include them during the current year. But if the extended harvestings cover a considerable or major part of the succeeding year, they should be included in that year.

14.48 Partial harvesting: This refers to so-called "reserve crops" among which is cassava, a very important food crop in West Africa. This occurs when the crop is planted in a greater quantity then normally required, often as a last crop in the shifting cultivation cycle, before land is returned to bush. Usually, only a part of the potential production is used, harvesting being done when needed over a course of time. Crop production is the consumption and is very difficult to estimate.

14.49 Scattered fruit trees: The number of fruit trees which are planted along field borders or scattered in fields and in other parts of a holding should be counted separately for each species, classified into those of bearing and non-bearing age. Total production from such trees can be calculated if the estimate of yield per tree is known from yield estimation surveys or by a subjective method of estimation. As yield from a scattered tree is likely to be different to that from a tree in a compact orchard (other things being equal), it is preferable to have a separate estimate of yield from scattered trees. The number of scattered trees of a fruit species can be converted into its area equivalent by applying a normal planting rate.

14.50 Enumeration of outside parcels: All parcels of a selected holding, whether they lie within or outside the selected primary sampling unit must be enumerated under that holding, provided they are not operated as a separate technical unit. It is possible that all parcels of a selected holding may be outside the selected primary sampling unit under a separate operator. Generally, such outside holdings will not be far away, but if so they can be enumerated by the nearest enumerator and the relevant questionnaire passed to the enumerator in charge of the selected holding.

14.51 Enumeration of nomadic livestock presents serious problems in some countries. Due to the scarcity of water or pasture lands or to other climatic conditions, the owners of livestock are forced to move together with their livestock from place to place in search of suitable grazing conditions. These people may be divided into three classes:

1. The whole tribe is on the move with their livestock and they do not practise cultivation in any place. These are considered purely nomadic.
2. The whole tribe is on the move with their livestock for the greater part of the year but practise cultivation for certain periods. These tribes are considered semi-nomadic.
3. The third class comprises tribes where some members of the group are sedentary and engaged in cultivation or other economic activities, and a part of the group moves with the livestock as herdsmen.

14.53 An alternative frame to be considered is water points. This can be of some use if a complete list of all water points, such as water holes, wells, etc., with information of degree of permanency of each well and adequate maps indicating location of these points, is available. However, in this frame there will always be a problem of coverage, as it will exclude the younger animals which are kept and watered near the camping place, and those herds which are watered on rivers and other sources which are not on the list of water points.

14.54 Apart from the problem of contacting the owners of the nomadic livestock, there is the problem of their reluctance to provide information to census authorities. This problem may be solved to a considerable extent by including as enumerators veterinarians and others who associate with the people and are known to the tribesmen, such as sons and other relatives of their tribes.

14.55 Shifting cultivation: As already stated, in an agricultural census the basic unit is the agricultural holding. However, a system of cultivation exists where holders clear certain parts in the reservoir of natural vegetation (forest or grass-woodland) for a short time and abandon them when the soil fertility is depleted. This system of cultivation is called "shifting cultivation".

14.56 In such cases the definition of a holding cannot be strictly applied. The total area of the holding should in such cases be considered as the sum of:

1. The area under crops during the reference period of the census, and
2. The area prepared for cultivation but not sown or planted at the time of the enumeration.

14.58 Collection and interpretation of data on the extent of shifting cultivation obtained from holders presents some problems, particularly in areas where settled agriculture is found together with shifting cultivation. There are different arrangements under which shifting cultivation can be practised. Most of the shifting cultivation is found under communal land tenure. The community (village, tribe, etc.) has ownership or cultivation rights over land area and is responsible for allocating pieces of land to individual holdings. Another form of shifting cultivation is practised by squatters, i.e., individual holders who are using pieces of land from natural forests and pastures (woods or bush) under circumstances where the rights of land ownership are ill defined or not protected. Shifting cultivation should not be confused with land rotation which, although similar in nature, is restricted to rotation of land owned (or in owner-like possession) by a single holder, while shifting cultivation refers to rotation of communal land or "nobody's" land.

14.59 Under the circumstances, it is not practical to ask the agricultural holders whether or not they are practising shifting cultivation, because they may not know any other system. Relevant data proposed to be collected from holders for each parcel are: (i) tenure of land and (ii) number of years under cultivation. Extent of shifting cultivation is then estimated on the basis of these data.

Supervision of field work

14.60 Supervision of field work, involving an element of surprise, in a sub-sample of holdings meets the twin objectives of keeping the enumerators on the alert and of assessing the nature and extent of errors being committed and of providing correction factors to the census results where found necessary. For the second objective to be achieved the supervisor has to record independently on prescribed forms (see example in Frame 14.2) the data on the questionnaires as actually found by him. More information concerning supervision is given in Chapters 11, 12 and 15.

Country.......................................  Name of the enumerator  .....................................  Province......................................  to be completed by the supervisor  (one sheet per enumerator)  Date of the supervision  Name of the village  Name of the holder  Number of verified parcels  Number of verified questionnaires  Difficulties met

Frame 14.2 Supervision Control Sheet

Procedure for collecting and forwarding completed questionnaires

14.61 The supervisors should be directly involved in collecting the questionnaires from the enumerators and forwarding them to the census headquarters. They can refer back to the enumerators all incomplete and incorrect work while in the enumeration area in order to rectify mistakes. The supervisors should be provided with guidelines not only for supervising the field work but also for scrutinizing completed questionnaires. Editing work at headquarters can be facilitated considerably if the supervisors are required to check the completed questionnaires for accuracy and consistency before forwarding them to headquarters.

Suggested reading
Casley D.J. and Lury D.A. (1981). Data collection in developing countries. Clarendon Press, Oxford.
INSEE (1962). Manuel d'enquêteur agricole (Service de coopération)
FAO (1965). Estimation of areas in agricultural statistics.
FAO (1966). Quality of statistical data (by S.S. Zarkovich).
FAO (1982). Estimation of crop areas and yields in agricultural statistics.
FAO (1992). Collecting data on livestock.
Idaikkadar N.M. (1979). Agricultural statistics: A handbook for developing countries. Pergamon Press, Oxford.
UN (1992). Handbook of population and housing censuses: Part I, Planning, organization and administration of population and housing censuses. Studies in methods, Series F, No. 54.
UN (1982). Non-sampling errors in household surveys: Sources, assessment and control. NHSCP technical study.