Hsien-Ming Lien Dept of Public Finance, NCCU Examine the data Hsien-Ming Lien Dept of Public Finance, NCCU

1.1 Read the data Read the ASCII file Read the excel file infile must provide the variable name, width, and format Read the excel file insheet variable names need to be specified Read the Stata file use c:\regstata\elemapi from the internet

cd dir use save

use http://www.ats.ucla.edu/stat/stata/webbooks/reg/elemapi

1.2 Describe the data Describe the data Data size Observations Variable name Variable type (string, byte, float, etc)

直接按ok

Variables api00/academic performance of the school acs_k3/the average class size in kindergarten through 3rd grade meals/the percentage of students receiving free meals full/the percentage of teachers who have full teaching credentials

List All observations Some observations Some variables

選取變數

Notice the missing values of meals. 

Codebook Number of values Missing values Distribution of values

選取變數後按ok

summarize Provide concise information about variables Observations Basic statistics (mean, s.d., min, max) Option: details

選取變數後按ok

1.3 Tab the data Tabulate Tabulate the size of class size

Look at the school and district number to check if they are from the same district

1.4 Graph the data Use graphs to examine the data Histogram Stem and leaf plot

A stem-and-leaf plot would also have helped to identify these observations.   This plot shows the exact values of the observations, indicating that there were three -21s, two -20s, and one -19.

Quiz 1: do a histogram on full Quiz 2: do a stem-and-leaf plot on full

Let's look at the frequency distribution of full to see if we can understand this better.  The values go from 0.42 to 1.0, then jump to 37 and go up from there. It appears as though some of the percentages are actually entered as proportions, e.g., 0.42 was entered instead of 42 or 0.96 which really should have been 96.

Again, let's see which districts these data came from.

We note that all 104 observations in which full was less than or equal to one came from district 401.  Let's count how many observations there are in district 104 using the count command.

Two ways graphs Scatterplot: show the joint distribution of two variables Let's look at the scatterplot matrix for the variables:

Correct the variable mistakes acs_k3 Replace the negative values into the positive ones replace acs_k3=-acs_k3 if acs_k3<0 Full Change from the percentage to the proportion replace full=full*100 if full<=1

save elemapi, replace