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Here is the capture from my lecture notes, and I am so confused with that notations.

For Several normal samples, can anyone show me how to write $x_{ij}$ in terms of vector form (involving $p$) and claim that $x_{ij}=0$ if $i\notin j$, otherwise $x_{ij}=1$

Moreover, for Simple linear regression, what's the point of indexing explanatory variables with the observed value, for different observed value, aren't they share the same explanatory variables.

Much appreciated for any comments.

  • $\begingroup$ Hi: For your second question, they share the same explanatory variables but the VALUE is different. $(y_{j}, x_{j})$ is not the same as $(y_{j}, x_{i})$. Unfortunately, I don't understand your first question. $\endgroup$
    – mlofton
    Jul 31, 2020 at 12:19
  • $\begingroup$ @mlofton cheers, you are right $\endgroup$
    – LJNG
    Jul 31, 2020 at 12:51


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