Ch5: fix stale continent subscripts in indicator functions

PR #578 caught that the first dummy-variable example is described with
subscript "Amer" while the text and the display equation below it both
refer to Asia. Fix that occurrence and the matching one in the display
equation, tidy the "in the Asia" wording, and clean up two other stale
subscripts in the fitted-value equation ("Euro" -> "Europe" and a
trailing space in "Oceania ").

Co-Authored-By: gerard314 <16446591+gerard314@users.noreply.github.com>
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EBuUHZXFqZKh7hEJxw5KvT

Author: claude

05-regression.qmd

@@ -1063,9 +1063,9 @@ We now write the equation for our fitted values $\widehat{y} = \widehat{\text{li
 $$
 \begin{aligned}
 \widehat{y} = \widehat{\text{life exp}} &= b_0 + b_{\text{Asia}}\cdot\mathbb{1}_{\text{Asia}}(x) + b_{\text{Europe}}\cdot\mathbb{1}_{\text{Europe}}(x) \\
-& \qquad + b_{\text{North America}}\cdot\mathbb{1}_{\text{North America}}(x) + b_{\text{Oceania}}\cdot\mathbb{1}_{\text{Oceania }}(x) \\
+& \qquad + b_{\text{North America}}\cdot\mathbb{1}_{\text{North America}}(x) + b_{\text{Oceania}}\cdot\mathbb{1}_{\text{Oceania}}(x) \\
 & \qquad + b_{\text{South America}}\cdot\mathbb{1}_{\text{South America}}(x)\\
-&= `r intercept` + `r offset_asia`\cdot\mathbb{1}_{\text{Asia}}(x) + `r offset_europe`\cdot\mathbb{1}_{\text{Euro}}(x)  \\
+&= `r intercept` + `r offset_asia`\cdot\mathbb{1}_{\text{Asia}}(x) + `r offset_europe`\cdot\mathbb{1}_{\text{Europe}}(x)  \\
 & \qquad + `r offset_north_america`\cdot\mathbb{1}_{\text{North America}}(x) + `r offset_oceania`\cdot\mathbb{1}_{\text{Oceania}}(x) \\
 & \qquad + `r offset_south_america`\cdot\mathbb{1}_{\text{South America}}(x)
 \end{aligned}
@@ -1081,10 +1081,10 @@ $$
 \right.
 $$
 
-In a statistical modeling context, this is also known as a *dummy variable*. \index{dummy variable} In our case, we consider the first such indicator variable $\mathbb{1}_{\text{Amer}}(x)$. This indicator function returns 1 if a country is in the Asia, 0 otherwise:
+In a statistical modeling context, this is also known as a *dummy variable*. \index{dummy variable} In our case, we consider the first such indicator variable $\mathbb{1}_{\text{Asia}}(x)$. This indicator function returns 1 if a country is in Asia, 0 otherwise:
 
 $$
-\mathbb{1}_{\text{Amer}}(x) = \left\{
+\mathbb{1}_{\text{Asia}}(x) = \left\{
 \begin{array}{ll}
 1 & \text{if } \text{country } x \text{ is in Asia} \\
 0 & \text{otherwise}\end{array}