Add notes about picking dispersion

lectures/lecture10/lecturenotes.tex

@@ -44,6 +44,7 @@
 
 \1 Mean, median, mode
     \2 \textit{When to use each}
+    \2 Categorical: mode, total: mean, skewed: median, else: mean
 
 \1 Covariance
     \2 Measure whether two random variables vary together 
@@ -70,7 +71,13 @@
 
 \1 TODO: Means of ratios
 
-\1 TODO: Picking index of dispersion
+\1 Picking index of dispersion
+    \2 Range (when bounded)
+    \2 Var or stddev (sttdev is in the right units) --- see also CoV
+    \2 Percentiles - 10 and 90, or 5 and 95 (want a sense of how long
+        things will take in extreme case
+    \2 SIQR (semi interquanile range): middle 50% / 2: very outlier-robust
+    \2 Mean absolute dev (use least)
 
 \1 Quantile-quantile plots
     \2 For each quartile: plot pairs of what the theoretical distribution