5. Frames for agricultural censuses and surveys
The agricultural census frame and the agricultural sample survey frames will be defined and discussed separately in the following sections in relation with the improvement of population data obtained from such agricultural data collection programmes.
In order to organize the agricultural census data collection, it is indispensable to estimate in advance the approximate location of the agricultural holdings or the holders' housing units and to assign to census enumerators well defined areas of work, known as enumeration areas.
The enumeration areas (EAs) are geographic areas (or groups of enumeration units) such that:
a) They constitute a partition, with no overlaps of:
- all the agricultural land, or
- ail agricultural holdings, or
- all holders' households, or
- all holders' housing units;
b) Their boundaries do not cross urban, rural or political subdivisions of the country;
c) Their area should correspond to approximately equivalent workloads estimated by:
- the approximate number of holdings or holders' households;
- the distances and difficulties of access to the holdings or holders' housing units;
- the average time needed for each interview and the established length of the census enumeration period.
An agricultural census frame is defined as an ordered list of enumeration areas (EA's), with the estimated number or addresses of holdings, or holders' households or holder's housing units in each EA.
The national population and housing census data and cartographic materials often provide the only or the most important source to construct the frames for the agricultural census. This is one of the reasons why it is of fundamental importance to coordinate adequately the population and the agricultural censuses, which in most countries are the largest, most expensive and most complex statistical data collection programmes.
It is important to coordinate the designs of the population and the agricultural censuses cartography/lists of EAs, or to elaborate them jointly, because this will save a considerable amount of time and resources. This is particularly significant for countries that can devote only very limited resources to national statistical data collection programmes, and to countries with a high proportion of population in the agricultural/rural sector.
The enumeration unit of the population and housing census is the household, and not the agricultural holding, the enumeration unit of the agricultural census.
Population census questionnaires, in most cases, do not allow a direct link to be established between holdings and holders. However, the population census questionnaires identify the population whose main activity is agriculture within the context of a fairly short reference period.
The universe of study of the population and housing census, i.e. the total number of households/housing units in the country, is larger than that of the agricultural census since the latter covers, in particular only a small proportion of urban households.
In urban areas in which the proportion of holders' households is generally low, in order to construct the agricultural census frame a field screening is often organized to permit the identification of the holder's households and of the agricultural census EAs by grouping contiguous population census EAs.
In rural areas, if the number of holders' housing units can be estimated from the total number of occupied housing units by EA, then suitable groups of contiguous population census EAs can be used to define the agricultural census EAs.
Consideration should be given to the following aspects of the population census questionnaires, related with the construction of the frame for the agricultural census:
1. The inclusion of questions aimed at identifying holders' households, such as obtaining the main and secondary occupation of the population during the agricultural year. And questions which differentiate between work performed on the respondents' holding and work performed on other holdings;
2. The inclusion of questions designed to provide information about some basic characteristics of holdings.
The definition of work performed by men and women in the holding, as already mentioned, should be carefully applied since women activities in the holding may be more difficult to detect due to cultural reasons.
The population census questions which distinguish between work performed on the respondents' holding and work performed on other holdings, and those questions that allow to identify holder's households are generally essential for constructing the agricultural census frame.
The construction of an agricultural census frame must also cover the holdings related to agriculture that are not directly associated with holders' households, such as large plantations or cooperatives. Although the population census may provide very useful data, it should not constitute the sole source of information for the construction of an agricultural census frame.
This section refers to agricultural sample surveys based on a list frame of holdings.
The frame for each stage of selection of an agricultural survey is defined as an ordered list of sampling units, together with their assigned measures of size.
For the type of agricultural survey considered in this section, the enumeration units and the ultimate sampling units are the holdings, the holders' households, the households or the housing units.
The most common sampling units and associated measures of size that define the frames for the first stages of selection of the agricultural surveys considered, are the following:
- Geographic areas. The measures of size associated with the sampling units are defined as a function of the estimated number of holdings or holders' households or households or housing units. For instance, the measure of size may be determined by the total number of housing units if the sampling unit is in a rural area and if there is a direct relationship between the total number of housing units and holders' housing units. Commonly used geographic sampling units are political subdivisions of a country, agricultural census EAs, or groups of contiguous population census EAs;
- Villages/localities or other population centres that lack precise geographic boundaries. The measures of size associated with these units are analogous, i.e. defined by the associated number of holdings or holders' housing units or housing.
Population and housing census data, enumeration areas and maps often constitute a highly important component in the construction of agricultural sample survey frames. In addition, in most cases the population census information is the best tool for detecting inconsistencies and verifying the validity of agricultural sample survey and census frames.
In view of the reasons above, the proper identification of holder's households in the Population and Housing Census is essential for the construction of the agricultural sample survey frames. For that purpose, the application of an adequate definition for work in agriculture performed by men and women should be considered.
As it was mentioned for the case of an agricultural census, the construction of an agricultural sample survey frame must also cover the holdings related to agriculture that are not directly associated with holders' households,
