diff --git a/10_data_sources.rmd b/10_data_sources.rmd
index b02340a..7ea16bc 100644
--- a/10_data_sources.rmd
+++ b/10_data_sources.rmd
@@ -43,6 +43,11 @@ Simon Fraser University Library: [Gender, Sexuality & Women's Studies Informatio
 [Gapminder](https://www.gapminder.org/data/) - all indicators displayed in Gapminder World
 
 
+<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">Anyone know of a good migration dataset? Ideally # of people moving from country i to country j by year</p>&mdash; Savage Jim (@jim_savage_) <a href="https://twitter.com/jim_savage_/status/1094672164928802816?ref_src=twsrc%5Etfw">February 10, 2019</a></blockquote>
+<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
+
+
+
 ### R packages
 
 
diff --git a/59_quantitative_methods.Rmd b/59_quantitative_methods.Rmd
index adeffc4..f2f6fbf 100644
--- a/59_quantitative_methods.Rmd
+++ b/59_quantitative_methods.Rmd
@@ -246,6 +246,15 @@ https://www.jstatsoft.org/article/view/v074i07
 ## Machine Learning
 
 
+
+
+## Principal Component Analysis (PCA)
+
+<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">New Video!<br>PCA (Principal Component Analysis), enjoy and share if you like it!<a href="https://t.co/9jvOIE4xAh">https://t.co/9jvOIE4xAh</a></p>&mdash; Luis G. Serrano (@luis_likes_math) <a href="https://twitter.com/luis_likes_math/status/1094479228035313664?ref_src=twsrc%5Etfw">February 10, 2019</a></blockquote>
+<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
+
+
+
 ## Random walk
 
 From wikipedia entry on [random walk](https://en.wikipedia.org/wiki/Random_walk):