“A new Approach to Improving Sample Design for Crop Forecast and Post – Harvest Estimates in Zambia” A Contributed Paper Session Presented at the International Conference on Agricultural Statistics (ICAS III), Westin Regina Hotel, Cancun, Q.R. Mexico 2nd-4th November 2004 By John Kalumbi Deputy Director – Agriculture & Environment Division Central Statistical Office (CSO) Lusaka, Zambia

I. INTRODUCTION AND INSTITUTIONAL ARRANGEMENT Production of Agricultural Statistics Responsibility of the CSO (Agric. & Environment Division)Responsibility of the CSO (Agric. & Environment Division) Collection of data is done in conjunction with the Ministry of Agriculture and Cooperatives (MACO) through the Early Warning and Data Base Management Unit.Collection of data is done in conjunction with the Ministry of Agriculture and Cooperatives (MACO) through the Early Warning and Data Base Management Unit. Agriculture & Environment Division Agriculture Branch Agriculture Branch Small & Medium Scale Farm SectionSmall & Medium Scale Farm Section Large Scale Farm SectionLarge Scale Farm Section

Environment Branch Environment Branch Land degradationLand degradation Air pollutionAir pollution Water SanitationWater Sanitation ForestryForestry WildlifeWildlife FisheriesFisheries Evolution of Agricultural Surveys in Zambia  The 1970/71 Census of Agriculture marked the beginning of annual agricultural surveys in Zambia. Crop Forecast Survey (CFS)Crop Forecast Survey (CFS) Post Harvest Survey (PHS)Post Harvest Survey (PHS) Area Measurement and Crop-Cutting Survey (AMCC) – has since been discontinuedArea Measurement and Crop-Cutting Survey (AMCC) – has since been discontinued

II. METHODOLOGY USED Survey sampling for both CFS and PHS for Small & Medium Scale agricultural holdingsSurvey sampling for both CFS and PHS for Small & Medium Scale agricultural holdings Complete enumeration for Large-Scale Agric. HoldingsComplete enumeration for Large-Scale Agric. Holdings Sample Design Cartographic census field operation defines Census Supervisory Areas (CSAs), which are further subdivided into Standard Enumeration Areas (SEAs)Cartographic census field operation defines Census Supervisory Areas (CSAs), which are further subdivided into Standard Enumeration Areas (SEAs) An SEA is the unit of data collection point at district levelAn SEA is the unit of data collection point at district level

Previous CFS/PHS Sample Design Based on 1990 census data Based on 1990 census data Only rural districts were covered Only rural districts were covered A stratified three stage sample design was used A stratified three stage sample design was used CSAs Primary Sampling Units (PSUs) selected at first stage with PPSCSAs Primary Sampling Units (PSUs) selected at first stage with PPS SEAs selected at second stage, with one SEA selected with PPS within each sample CSASEAs selected at second stage, with one SEA selected with PPS within each sample CSA Measure of size in both cases is number households as listed in the 1990 census of population and Housing.Measure of size in both cases is number households as listed in the 1990 census of population and Housing. A total sample of 405 SEAs was drawn out of 9,000 rural SEAsA total sample of 405 SEAs was drawn out of 9,000 rural SEAs No provision of replacement of both sample SEAs and sample households.No provision of replacement of both sample SEAs and sample households. Sample households were selected at third stage from the listing stratified by farm size category using Linear Systematic Sampling (LSS) procedure with random start.Sample households were selected at third stage from the listing stratified by farm size category using Linear Systematic Sampling (LSS) procedure with random start.

New CFS/PHS Sample Design Based on 2000 census data Based on 2000 census data A stratified two-stage sample design is now being used A stratified two-stage sample design is now being used SEAs are the Primary Sampling Units (PSUs) selected at first stage with PPSSEAs are the Primary Sampling Units (PSUs) selected at first stage with PPS Measure of size is number of agricultural households as listed in the 2000 census of population and housingMeasure of size is number of agricultural households as listed in the 2000 census of population and housing A total sample of 410 SEAs were drawn out of the 12,788 agricultural SEAs as defined for the 2000 Zambia CensusA total sample of 410 SEAs were drawn out of the 12,788 agricultural SEAs as defined for the 2000 Zambia Census Sample households are selected at the second stage from the listing stratified by farm size category (land area, number of animals, special crops criteria)Sample households are selected at the second stage from the listing stratified by farm size category (land area, number of animals, special crops criteria)

Other Features of New CFS /PHS Sample Design Includes a small fraction (5%) of urban SEAs, i.e, urban SEAs in which 70 percent or more households are agricultural according to the 2000 Zambia census data (about 586 urban SEAs in total) Includes a small fraction (5%) of urban SEAs, i.e, urban SEAs in which 70 percent or more households are agricultural according to the 2000 Zambia census data (about 586 urban SEAs in total) Has provision for the replacement of any sample SEAs that may not be enumerated for one reason or another in order to maintain the effective sample size. Has provision for the replacement of any sample SEAs that may not be enumerated for one reason or another in order to maintain the effective sample size. Eight (8) crops were identified to receive special treatment at second sampling stage in order to improve the precision of survey estimates of crop area and production (i.e., these are crops with limited geographical concentration whose CVs previously were relatively high due to the smaller number of observations – sorghum, rice, cotton, burley tobacco, Virginia tobacco, sunflower, soybeans, and paprika) Eight (8) crops were identified to receive special treatment at second sampling stage in order to improve the precision of survey estimates of crop area and production (i.e., these are crops with limited geographical concentration whose CVs previously were relatively high due to the smaller number of observations – sorghum, rice, cotton, burley tobacco, Virginia tobacco, sunflower, soybeans, and paprika)

III. STRATIFICATION OF HOUSEHOLDS Previous sample design Included households listed in sample SEAs by two farm size categories: Included households listed in sample SEAs by two farm size categories: Category A: 0 – 4.99 hectaresCategory A: 0 – 4.99 hectares Category B: 5.0 – hectaresCategory B: 5.0 – hectares New sample design Stratification of households listed in sample SEAs is based on Stratification of households listed in sample SEAs is based on Farm size (land area) categoryFarm size (land area) category Number of livestock or poultry raised criteriaNumber of livestock or poultry raised criteria Growing of special crops criteriaGrowing of special crops criteria

Stratification of households by farm size (land area) Category A: 0 – 1.99 hectaresCategory A: 0 – 1.99 hectares Category B: 2.00 – 4.99 hectaresCategory B: 2.00 – 4.99 hectares Category C: 5.00 – hectaresCategory C: 5.00 – hectares In both the previous and new sample design, households with farm size category of 20 or more hectares were/are included in the special frame for large- scale farmers and are enumerated separately.

Stratification of households by number of livestock or poultry raised criteria Stratification of households by number of livestock or poultry raised criteria Based on the number of livestock or poultry raised, households are added to category C if the following minimum number are being raised: Based on the number of livestock or poultry raised, households are added to category C if the following minimum number are being raised: Cattle – 50Cattle – 50 Pigs – 20Pigs – 20 Goats – 30Goats – 30 Poultry – 50Poultry – 50

Stratification of households by growing of special crops criteria Households may be added to category B and C based on the special crops treatment criteria Households may be added to category B and C based on the special crops treatment criteria If the sample SEA only has 1 or 2 households with any of these special crops, these households will be asigned to category C ( in case they do not qualify based on land area and animals)If the sample SEA only has 1 or 2 households with any of these special crops, these households will be asigned to category C ( in case they do not qualify based on land area and animals) If the sample SEA has only 3 to 5 households with any of these special crops, such households are assigned to category B (if they were previously assigned to category A based on land area and livestock)If the sample SEA has only 3 to 5 households with any of these special crops, such households are assigned to category B (if they were previously assigned to category A based on land area and livestock)

IV. SAMPLE HOUSEHOLDS SELECTION IN SAMPLE SEAs Total sample size for each SEA – 20 households Total sample size for each SEA – 20 households Distribution of sample households to each category: Distribution of sample households to each category: Category C – 10Category C – 10 Category B – 5Category B – 5 Category A – 5Category A – 5 If there are shortfall in category C, the difference from 20 will be allocated equally to categories B and A or category B will have one more sample households than category A, if the difference cannot be allocated equally. If there are shortfall in category C, the difference from 20 will be allocated equally to categories B and A or category B will have one more sample households than category A, if the difference cannot be allocated equally. Where there is no household in category C and less than 10 in category B, the difference from twenty will be met from category A. Where there is no household in category C and less than 10 in category B, the difference from twenty will be met from category A. If all listed households fall in category A, then all 20 sample households will come from category A. If all listed households fall in category A, then all 20 sample households will come from category A. For each category in the sample SEA, selection of sample households is done using Linear Systematic Sampling (LSS) Procedure with random start.For each category in the sample SEA, selection of sample households is done using Linear Systematic Sampling (LSS) Procedure with random start.

V. ESTIMATION Estimating for the total involves the weighing of variables before additions are made at district, provincial and national levels. The basic sampling weight is obtained as inverse of the probabilities of selecting the SEAs and households by category size. The formula for estimating the survey estimates of a total is as follows: ^ Y =     W shi Y shij h i s j h i s jWhere: Y shij = value of variable y for the j-th sample household in category s within the i-th sample SEA in district hY shij = value of variable y for the j-th sample household in category s within the i-th sample SEA in district h W shi = basic weight for the sample households in category s within the i-th sample SEA in district h.W shi = basic weight for the sample households in category s within the i-th sample SEA in district h.