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- </header>
-
- <h1>Estimate a limit of quantification (LOQ)</h1>
-
-<div class="row">
- <div class="span8">
- <h2>Usage</h2>
- <pre><div>loq(object, ..., alpha&nbsp;=&nbsp;0.05, k&nbsp;=&nbsp;3, n&nbsp;=&nbsp;1, w.loq&nbsp;=&nbsp;"auto", var.loq&nbsp;=&nbsp;"auto", tol&nbsp;=&nbsp;"default")</div></pre>
-
- <h2>Arguments</h2>
- <dl>
- <dt>object</dt>
- <dd>
- A univariate model object of class <code><a href='http://www.inside-r.org/r-doc/stats/lm'>lm</a></code> or
- <code><a href='http://www.inside-r.org/r-doc/MASS/rlm'>rlm</a></code>
- with model formula <code>y ~ x</code> or <code>y ~ x - 1</code>,
- optionally from a weighted regression. If weights are specified
- in the model, either <code>w.loq</code> or <code>var.loq</code> have to
- be specified.
- </dd>
- <dt>alpha</dt>
- <dd>
- The error tolerance for the prediction of x values in the calculation.
- </dd>
- <dt>...</dt>
- <dd>
- Placeholder for further arguments that might be needed by
- future implementations.
- </dd>
- <dt>k</dt>
- <dd>
- The inverse of the maximum relative error tolerated at the
- desired LOQ.
- </dd>
- <dt>n</dt>
- <dd>
- The number of replicate measurements for which the LOQ should be
- specified.
- </dd>
- <dt>w.loq</dt>
- <dd>
- The weight that should be attributed to the LOQ. Defaults
- to one for unweighted regression, and to the mean of the weights
- for weighted regression. See <code><a href='massart97ex3.html'>massart97ex3</a></code> for
- an example how to take advantage of knowledge about the
- variance function.
- </dd>
- <dt>var.loq</dt>
- <dd>
- The approximate variance at the LOQ. The default value is
- calculated from the model.
- </dd>
- <dt>tol</dt>
- <dd>
- The default tolerance for the LOQ on the x scale is the value of the
- smallest non-zero standard divided by 1000. Can be set to a
- numeric value to override this.
- </dd>
- </dl>
-
- <div class="Value">
- <h2>Value</h2>
-
- <p><dl>
- The estimated limit of quantification for a model used for calibration.
-</dl></p>
-
- </div>
-
- <div class="Description">
- <h2>Description</h2>
-
- <p>The limit of quantification is the x value, where the relative error
- of the quantification given the calibration model reaches a prespecified
- value 1/k. Thus, it is the solution of the equation
- $$L = k c(L)$$
- where c(L) is half of the length of the confidence interval at the limit L
- (DIN 32645, equivalent to ISO 11843). c(L) is internally estimated by
- <code><a href='inverse.predict.html'>inverse.predict</a></code>, and L is obtained by iteration.</p>
-
- </div>
-
- <div class="Note">
- <h2>Note</h2>
-
- <p>- IUPAC recommends to base the LOQ on the standard deviation of the signal
- where x = 0.
- - The calculation of a LOQ based on weighted regression is non-standard
- and therefore not tested. Feedback is welcome.</p>
-
- </div>
-
- <h2 id="examples">Examples</h2>
- <pre class="examples"><div class='input'>data(massart97ex3)
-attach(massart97ex3)
-m &lt;- lm(y ~ x)
-loq(m)
-</div>
-<div class='output'>$x
-[1] 13.97764
-
-$y
- 1
-30.6235
-
-</div>
-<div class='input'>
-# We can get better by using replicate measurements
-loq(m, n = 3)
-</div>
-<div class='output'>$x
-[1] 9.971963
-
-$y
- 1
-22.68539
-
-</div></pre>
- </div>
- <div class="span4">
- <!-- <ul>
- <li>loq</li><li>loq.lm</li><li>loq.rlm</li><li>loq.default</li>
- </ul>
- <ul>
- <li>manip</li>
- </ul> -->
-
- <h2>See also</h2>
-
- Examples for <code><a href='din32645.html'>din32645</a></code>
-
-
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