title: Difference between the interaction : and * term for formulas in StatsModels OLS regression
body: <p>Hi I'm learning Statsmodel and can't figure out the difference between : and * (interaction terms) for formulas in StatsModels OLS regression. Could you please give me a hint to figure this out?</p>
  
  <p>Thank you!</p>
  
  <p>The documentation:
  <a href="http://statsmodels.sourceforge.net/devel/example_formulas.html" rel="noreferrer">http://statsmodels.sourceforge.net/devel/example_formulas.html</a></p>