aria-label="anchor" href="#change-and-trend-analysis"></a>
</h3>
<p>To demonstrate change analysis, we use the <code>NRSA_EPA7</code>
data. There are several variables in <code>NRSA_EPA7</code> you will use
next:</p>
<ul>
<li>
<code>SITE_ID</code>: a unique site identifier</li>
<li>
<code>WEIGHT</code>: the survey design weights</li>
<li>
<code>NITR_COND</code>: nitrogen condition category
(<code>Good</code>, <code>Fair</code>, and <code>Poor</code>)</li>
<li>
<code>BMMI</code>: benthic macroinvertebrate mu