Degree of reproducibility of measurements. Variations are largely due to the appropriate use of techniques, concentration of the technician Sometimes linked to the difficulty of the test Precision

The degree by which we approach with our measurements the true value. Differences are due to standardised errors or inappropriate techniques or instrument variation Accuracy

Purpose: identify measurement errors in terms of precision and accuracy. Procedure: take 10 measurements in duplicate in two batches (10 persons and repeat on the same persons) Precision: determine the combined variation between measurement 1 and 2. –Calculate the absolute difference between measurement 1 and 2 (a-b) –Square the difference (a-b) 2 –Sum the differences  (a-b) 2 –The smallest figure yields the highest precision Interpretation is against a “supervisor”, i.e. “the reference – the individual  (a-b) 2 should not be more than twice the variation of the supervisor Standardisation exercise

Standardisation precision table

Measure the difference between a field worker’s values and those of a reference or supervisor. (the reference can also be the average of all the measurements of the technicians Procedure: –sum de measurements: (a+b) –Square the sum = (a+b) 2 –Subtract the above value from the value from the reference –Square this difference and add up –This value should not be more than twice the total inter- measurement variation from the supervisor or reference Standardisation Accuracy

Standardisation Accuracy table

Standardisation 2