title: Interpretation of coefficienets and their interactions of Linear regression in R
body: <p>I would like to know how to interpret the coefficients for &quot;intercept&quot; and &quot;interactions&quot;
  my interactions include: 1) numerical variable age: and binary smoker. 2) two dummy variables Obese:Smoker</p>
  <p>Also I do I interpret the negative coefficient of this interaction?</p>
  <p>my model is this with the following out put:</p>
  <pre><code>lm(log(charges) ~ age + children + age*smoker + smoker*obese , data = train)
  
  Coefficients:
                    Estimate Std. Error t value Pr(&gt;|t|)    
  (Intercept)       8.268120   0.045495  181.74   &lt;2e-16 ***
  age               0.025017   0.001046   23.91   &lt;2e-16 ***
  children          0.109758   0.009886   11.10   &lt;2e-16 ***
  smoker1           2.465854   0.089212   27.64   &lt;2e-16 ***
  obeseyes          0.339899   0.029693   11.45   &lt;2e-16 ***
  age:smoker1      -0.033310   0.002091  -15.93   &lt;2e-16 ***
  smoker1:obeseyes  0.706296   0.059444   11.88   &lt;2e-16 ***
  </code></pre>
  <p>Is intercept interpreted as the average medical cost for reference group of &quot;non-smokers&quot; and &quot;not-obese&quot; or I am totally wrong?</p>