File size increase by import/export from/to Stata
Hi,

I have noticed that importing/exporting data from/to Stata seems to increase file size a lot (sometimes more than double). I thought it mostly was caused by export to Stata, where string variables would be initially set to a length of 256 or something like that (usually after exporting I have to run the compress command in Stata and save the file again in order to save space). But now I noticed that importing data in Stata format and then exporting it to CSV causes similar increases in file size, even after dropping variables from the original file (so one would expect the file to be smaller). Any ideas of what is going on? 

An example of a stata file with the exported csv file and script can be found [here](https://www.dropbox.com/s/xdimn6k40t7fmf4/Export_filesize_issue.zip?dl=0).

I ran the following commands in a script (included in the zip file):

```
#!/usr/bin/env python
# coding: utf-8
from __future__ import division
import sys, os, time
# Math, data
import numpy as np
import pandas as pd

# Print filesize original
print('Original filesize= '+str(os.path.getsize('./cn59_mat.dta'))) #Original filesize= 2883761
# Load data
df=pd.read_stata('cn59_mat.dta')
# Drop one variable
df.drop('index', axis=1, inplace=True)
# Export
df.to_csv('cn59.csv', encoding='utf-8', index=False)
# Print filesize original
print('New filesize= '+str(os.path.getsize('./cn59.csv'))) #New filesize= 4984671
```

So as you can see it doubled in size. I am using Python 2.7.6 with Pandas 0.15.1 on OS X 10.9.
