Transforming a sample design for taking into account new statistical needs, new information or new technological instruments for data collection Elisabetta Carfagna Professor, University of Bologna, Italy

Background and justification Various agricultural statistical systems New statistical needs New low cost technological instruments for data collection –GPS –PDAs New information is available (e.g. a land cover map produced for controlling subsidies)

Alternative strategies First strategy: the sample design adopted in the previous years is preserved Second strategy: the sample design is conceived ex novo Third strategy: small changes are applied to the sample design

Italy, Agrit project from early 90’s to 2000 From early 90’s to 2000 –Stratified random sampling of about 5,000 segments with physical boundaries –Stratification: land cover map from photo- interpretation of Landsat TM images

POPOLUS Availability of POPOLUS: –grid of points 500 meters apart –photo-interpreted according to land cover legend –geometrically corrected photos, scale 1:10,000 POPOLUS first phase sample (used for stratification)

Agrit project from 2002 From 2002 Two phase stratified random sampling of 84,000 un-clustered points –CVs less than 5% for main crops at national level

Agrit new technological instruments From 2009 Ultra Mobile Personal Computer (UMPC) - PDA with GPS and GPRS/UMTS and Wi-Fi connection Data collected immediately sent to the central acquisition unit Change of quality control

Refresh project for control of declaration Availability of new information: “Refresh” project for control of declaration of farmers ( ) –Photo-interpretation for the whole Italian territory of: geometrically corrected aerial photos very high resolution satellite images with spatial resolution 0,5 m POPOLUS update

New information needs Baseline indicators for agro-environmental policy and rural development policy (EU) –Agro-environmental parameters –Farmland of high naturalistic value –Risk of erosion

Observation on small circle around the point Observations on small circle around the point –Irrigation –Grass or bare soil (for permanent crops)

Observations on square segments Observations on square segments: –Irrigation, presence and kind –Erosion, presence and level –Bushes –Small wood lots –Isolated trees etc.

Pilot project Pilot project for: –Detecting the problems of the ground survey –Evaluating the variance of the variables –Computing sample size –Identifying the optimum segment size

First strategy-preserving the sample design Advantages of preserving the sample design –Perfect comparability over time –Change detection –Experience of the project managers and of the enumerators –The reliability of the data collection procedures has already been assessed

First strategy-preserving the sample design Disadvantages of preserving the sample design –New information (e.g. land cover map) cannot be used at the design level –Only some new parameters can be estimated –Cannot take complete advantage from the characteristics of new technological instruments

Second strategy-sample design conceived ex novo Advantages of conceiving the sample design ex novo –New statistical needs satisfied –New available information used at the design level –Maximum advantage from new technological instruments for data collection

Second strategy-sample design conceived ex novo Disadvantages of conceiving the sample design ex novo –Not complete comparability –Difficult change detection –Project managers and the enumerators have to adapt to new procedures –Reliability of the data collection procedures has to be assessed –Cost

Third strategy-small changes Advantages of small changes –New statistical needs partially taken into account –Comparability over time –Experience of the project managers and of the enumerators –Reliability of the data collection procedures

Third strategy-small changes Disadvantages of small changes –New information (e.g. land cover map) cannot be used at the design level –Few new parameters can be estimated –Partial advantage from new technological instruments for data collection

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