1.5:
Systematic Error: Methodological and Sampling Errors
Systematic errors, depending on their source, are of four types – sampling, instrumental, method, and personal errors.
Sampling errors occur due to improper sampling methods, which leads to variation between replicate samples. A refined sampling strategy minimizes these errors.
Instrumental errors arise from defective instruments or faulty calibrations These errors can be eliminated by periodic calibration.
Method errors stem from limitations in the analytical method, non-ideal behavior of reagents, and invalid assumptions. These errors can be mitigated using standard reference materials, blank tests, or conducting a parallel independent analysis.
Furthermore, personal errors are a result of carelessness and the limited abilities of analysts. These can be minimized via systematic, attentive laboratory work, and automated procedures.
If the magnitude of absolute error is independent of the sample size, then it is a constant error. However, if it varies systematically with the sample size, it is a proportionate error.
1.5:
Systematic Error: Methodological and Sampling Errors
In the case of systematic errors, the sources can be identified, and the errors can be subsequently minimized by addressing these sources. According to the source, systematic errors can be divided into sampling, instrumental, methodological, and personal errors.
Sampling errors originate from improper sampling methods or the wrong sample population. These errors can be minimized by refining the sampling strategy. Defective instruments or faulty calibrations are the sources of instrumental errors. Periodic calibration of instruments is essential to eliminate such errors.
Method errors occur due to the limitations in an analytical method, the non-ideal behavior of reagents used, and invalid assumptions made while setting up the measurement. These errors can be mitigated using standard reference materials or analysis independent of the existing method but carried out in parallel.
Personal errors arise due to analysts' carelessness or lack of skill. Proper organization of materials and equipment, standardization of protocols, and attention to detail can help minimize these errors. Automated procedures can also be instituted to minimize human handling, reducing personal errors.
Systematic errors can also either be constant errors or proportional errors. The absolute magnitude of constant errors remains the same irrespective of the sample size. These errors can be minimized by increasing the sample size, as the contribution from the constant error relative to a larger sample size is less significant than the same constant error relative to a smaller sample size. On the other hand, a proportional error will increase in magnitude with increasing sample size, hence the term 'proportional.' Increasing the sample size will not help to reduce these types of errors. Using high-precision instruments is one way of reducing proportional errors.