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

elisabetta.carfagna@unibo.it

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 projectfrom 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 (2009-2010)– 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

Thank you for your attention

elisabetta.carfagna@unibo.it