LPISQA Legacy/ETS/Decisions

From Wikicap - European Commission

Limiting Quality (LQ) indeces applicable to the different quality elements

Limiting Quality indices are used to determine the acceptance number for attribute sampling:

  • QE4 - for 1% / LQ2 : please look at slides 13-14 of this presentation
  • QE2 - QE3 - QE5 for 5% / LQ8 (theoretically). Hower the Commission services suggest to move from LQ8 to LQ12.5. Although this LQ substitution mimics a bit the choice recommended in 3.5.1 of ISO2859-2 on AQL/LQ ratio.

The resulting acceptance numbers are indicated in this table.

Lot size LQ=2,0% LQ=8,0% LQ=12,5%
35 001 to 150 000 n
150 001 to 500 000 n
> 500 000 n

QE1 and QE7 both measure are variable values, but do not count as non-conforming items. This allows direct application of the expectation error rates. There is no expression of applicable LQ.

Denominators for the acceptance decisions

During the inspection procedure, it can happen that not all parcels in the particular scope can be successfully inspected, e.g. because of a critical defect, or because of the absence of information in IACS for the inspection year. Therefore it is absolutely normal that the resulting of acceptance decisions becomes smaller than the original scope.

In general the inspection is targeted at the total population of the sample. However, not all the parcels can be inspected. Those parcels that can be inspected constitute the subpopulation. In other words the subpopulation excludes the skipped parcels, but includes the critical defects. For a particular year N the denominators used in the various quality elements are the following:

  • QE1: subpopulation minus RP parcels that cannot be measured (note: some critical defects are measurable!)
  • QE2: idem
  • QE3: total population
  • QE4: total population
  • QE5: sub-population minus RP that are not declared during year N minus RP that cannot be measured
  • QE6: (2010) all applications
  • QE7: (2010) all application

EXAMPLE 1: In case of total population of 1466 parcels can yield the following denominators (underlined):

  • Subpopulation: 1250
  • skipped: 113 (i.e. technically impossible to inspect)
  • measured (QE1 and QE2): 1197 (out of which 1115 by digitising, 82 by area recovery)
  • declared: 1226
  • declared AND measured (QE5): 1183
  • total population (QE3 and QE4):1466
  • all applications (QE6 and QE7):68781

NOTE: Area declared is defined in the scope of Article 56 of 112/2009. It involves declaration for aid schemes and for other uses.


Subset Parameter Example
pre-selection sample N 3750
number that is skipped (for technical reasons) Nskip 27
number that is inspected Ninsp 1250
number that is measured (digitised ot derived) Nmeas 1186
number that has comparable information Ncomp 1093
number that are non-conforming for QE2 Nncqe2 16
number that is non-conforming for QE4 Nncqe4 4
number that is non-conforming either for QE2 or QE4 Nncqe2/4 18
number that is conforming for QE2 (=Ncomp-Nncqe2) Ncqe2 1077
number of non conforming or defective parcels due to faled update (i.e. cause A) Nncqe3(A) 7

The numbers defined above are relevant for the seven quality measures as indicated by this second table:

QEx number in DQ_scope nominator denominator comment
QE1 Nmeas n/a n/a
QE2 Ncomp Nncqe2 Ncomp
QE3 Nncqe2/4 Nncqe3 Ninsp
QE4 Ninsp Nncqe4 Ninsp
QE5 Ncqe2 n/a n/a
QE6 Ninsp n/a n/a uses Nncqe3(A)
QE7 Ninsp n/a n/a uses Nncqe2/4 and Ninsp

NOTE: in both tables the number Ninsp equals to the determined sample size and represents both the DQ_scope and the denominator for QE4.

Once missing to meet a threshold is not necessarily a problem, why are they introduced?

The thresholds are important and should be kept, as they give the opportunity to the MS to decide whether an action needs to be taken. The threshold represent the benchmarks needed to evaluate a system.

Conformity of non-measurable RP without critical defect but containing an ineligible element

A non-measurable RP that contains an ineligible element, but does not contain any critical defect is retained to be conformant. This is justified the definition of the “non-conformant’’ category, which is applicable only on RP that are measurable. The ineligible element causes non-conformity through contamination for measured parcels only.

Why the 2% threshold is applied? (QE 1)

This threshold is defined as "materiality threshold", i.e. a benchmark for serious error in the Court of Auditors DAS methodology – and the related update.

Why the 3% threshold is applied? (QE 2)

This threshold difference is specified (twice) in 2009R1122 for a comparison between an area observed and an area declared.

  • In Article 58: Reductions and exclusions in cases of over-declaration: the area declared for the purposes of any area-related aid schemes, ..., exceeds the area determined ...if that difference is more than either3 %...
  • In Article 55: Non-declaration of all areas: the difference between the overall area declared in the single application ... and the area declared plus the overall area of the parcels not declared, ..., is more than 3 % of the area declared.

NOTE 1: In a good LPIS “Area declared” should be derived from the LPIS reference area.

NOTE 2: The technical tolerance for smaller parcels (as add on to 3%) is 5 % and 7%.

NOTE 3: The maximum tolerance of OTSC methodology is 1ha.

Tolerances for area based conformity (QE 2)

The Commission services acknowledge that non-conformity based on exceeding an area difference threshold is influenced by the parcel size, the characteristics of source image, the landscape (accuracy of orthorectification) and the interactions between them. The general expectation for area based conformity is based on 3% accuracy on the mean polygon measurement uncertainties with 50 cm GSD imagery. Considering that Member states have some control over their source imagery, a dependency of the conformity threshold and the parcel size has been introduced.

Reference area Conformity threshold
> 5000 m2 3 %
2000 – 5000 m2 5 %
< 2000 m2 7 %

In the LPIS QA methodologically Member States have to report the “distribution of reference parcels where the maximum eligible area takes ineligible areas into account or where it does not take agricultural area into account” with the raw observed data. This categorisation should be assessed using the variable threshold included above. In addition, for QE2 an additional scoreboard entry has been introduced indicating the number of non-conforming parcels smaller than a threshold size.

NOTE 1: Introducing these size dependent thresholds creates "safety margins" of up to 140m2 or bigger and 250m2 for the smaller parcel. It may also result that parcels with a newly constructed building inside the LUI would easily escape the detection when only this area-based conformance test is applied. To prevent this the guidance introduces a separate conformance test on the ineligible features inside the LUI.

NOTE 2: This tolerance may obscure analysing the field situation by vindicating (“hiding”) parcels whose shape and size prevent accurate and precise measurements. Although a given LPIS might well be the most appropriate design for the prevailing conditions, it is essential to become aware of issue and its implications of the choices made in the LPIS.

The Commission services do not consider introduction of new / other tolerance being good practice.

Why the 5% threshold is applied? (QE 3)

It is an arbitrary value. It serves an indicator/alert function.

How to deal with causes of non-conformity? (QE 3)

Hereby we list some examples how non-conformity can be treated depending on its nature: Latest imagery is not fit for inspection:

  • Skip the RP
  • Add new non-conformity code, related to the limitation of the VHR
  • Add Waiver

Time difference between exchange of data (either raster of vector) and QA-inspections

  • Add a new non conformity code: imagery contains changes not yet reported on the imagery used for refresh

National legislative requirements (splitting due to administrative boundaries)

  • Add a new non-conformity code, LUI contains administrative national boundaries.
  • Apply the appropriate waiver from the list

Why Limiting Quality (LQ) is set to 2? (QE 4)

LPIS should have no true critical defects at all. The limiting quality (in percent nonconforming parcels) is set to 2 as it is the "materiality threshold" defined for serious error in the Court of Auditors DAS methodology and its update.

Why the threshold is set to 25%? (QE 6)

It is arbitrary: serves an indicator/alert function; i.e. keeping track of the changes in the land.

Applicable threshold for QE7?

The applicable threshold is 2%, which is is the "materiality threshold" defined for serious error in the Court of Auditors DAS methodology and its update.

Additional criterion on good quality management principles: the threshold should not significantly higher than the previous year.