*Thyne, Clayton
*Intro to Stats, Chapter 9 examples

	clear
	set mem 80m
	cd [your directory]

*  NOTE: the above command asks you to change the directory.  The directory will depend on how you've set up
*  the folders on your computer.  For example, my command is...
*  cd F:\teaching\Fall_2008\PS572-401-baby_stats\do_file_directories\chapter9
*  This is necessary so you know where stata is saving things.

****Part 1: review of difference of means
	use "http://www.uky.edu/~clthyn2/intro_stats/CH9_example.dta"
	ttest UK=IA
	*We see that the C.I. includes zero, so we cannot reject the null.

*Now, let's make our sample 1000 with the same mean.
	expand(100)
	ttest UK=IA
	*With this larger sample, we can indeed conclude that IA GPAs are
	*significantly lower than UK GPAs.

****Part 2: examining statistical and substantive significance
	clear
*We draw 2 normal samples of undergrads with mean=3.1 for UK students...
*and mean=3.14 for IA students
	drawnorm UKgpa IAgpa, n(10000) means(3.1, 3.14) sds(1, 1)
*Now, is there a statistically significant difference?
	ttest IA=UK
*Yes, the two samples are statistically different, ...
*but is the difference meaningful?

	hist UKgpa, xline(3.080696) frequency saving(UKgpa.gph, replace)
	hist IAgpa, xline(3.130526) frequency saving(IAgpa.gph, replace)

	graph combine UKgpa.gph IAgpa.gph

****Part 3: data for the in-class example
	clear
*First, we generate some fictitious population of the world...
	drawnorm age, n(100000) sds(8)
	replace age=age+35
	sum

****Part 4: using the t table

**Part 4a
	clear
	use "http://www.uky.edu/~clthyn2/intro_stats/data_set_1.dta"
	gen lttrade=log10(ttrade)
	sum lttrade if western~=1
*So, using the formula on page 295...
	*t = the value from Table V that we decide (our alpha)
	*Xbar = the threshold we'll calculate
	*mu = 3.649 (the full-sample mean trade)
	*sigma = .725 (SD from below)
	*sqrt(n) = 10.25 (sqrt(105))

*Let's choose alpha=.05, so t= 1.64 (one tailed)
*look at the formula in notes with these values...

**Part 4b: looking for significance
	sum lttrade if western==1