To perform a Principal Component Analysis (PCA), it is generally necessary to have a dataset collected over several years. However, some laboratory analyses for certain parameters report results as detection limits, for instance, values expressed as ≤0.001 mg/L.

An illustrative case is that of Suspended Solids (SST), where the reported values are:

• Day 1: 0.05 mg/L
• Day 2: 0.04 mg/L
• Day 3: ≤0.01 mg/L

In situations like this, the question arises: How should we handle values reported as detection limits, such as ≤0.01 mg/L? Should these be considered as 0.01 mg/L (the detection limit value) or as 0 mg/L (absence of the parameter)? This decision is particularly important when calculating averages or medians, as the way these data are treated can significantly affect statistical analysis and the final interpretation of the PCA.