title: How to run State Level Fixed Effects with PLM
body: <p>I am trying to run a regression with only state level fixed effects, but not time fixed effects. </p>
  
  <p>I am trying:</p>
  
  <p><code>lm1 &lt;- plm(lnwage ~ age + age^2 + education, data = cps, index = "state", model = "within")</code></p>
  
  <p>But I am not having any luck, and I am only finding information online of people using state and time fixed effects at the same time.</p>