Estimating the detection limit of a measurement system

Estimate the limit of detection of a measurement system or procedure.

  1. Select a cell in the dataset.
  2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Precision and then click Detection Capability.
    The analysis task pane opens.
  3. In the Y drop-down list, select the measured variable.
  4. In the By drop-down list, select the level variable, and then:
    • If the values are identifiers, select the Identifier check box, and then in the Assigned values grid, under the Value column alongside each level, type the value.
    • If the values are relative dilutions made by mixing high and low pools, select the Relative values check box, and then in the Assigned values grid, under the Value column for the first and last level, type the value (intermediate values are automatically calculated using relative values).
    • If the values are known/expected/assigned values, select the Known values check box.
    Note: Computation of detection limits only requires the assigned value of 0 for blank materials. You do not need to assign values to other materials.
  5. In the LoB Estimator drop-down list, select:
    Option Description
    Normal quantile Estimate the LoB using the 5% upper of the distribution of blank values (levels with assigned value 0).

    Use when values are normally distributed and not truncated at 0.

    Quantile Estimate the LoB using the 95th percentile of the distribution of blank values.

    Use when values are truncated at zero.

    Known value Use specific value as the LoB.
  6. In the Alpha edit box, type the probability that a blank material gives a result greater than the critical value (LoB), when in fact the substance is not present (typically 5%).
  7. In the Beta edit box, type the probability that a non-blank material gives a result less than the critical value (LoB) when in fact the substance is present (typically 5%).
  8. Click Calculate.