title: Converting quarterly time-series data into monthly data
body: <p>I am trying to use a quarterly price deflator on monthly housing data. Can you please help me convert the quarterly data into monthly data? I looked into using the Cubic Spline Interpolation method in Stata but had no luck getting the do file to work. I have access to excel and R so those are an option for me to try. Thank you for your time. </p>
  
  <pre><code>Quarterly       CPI Deflator Data    
  1999-04-01  79.891
  1999-07-01  80.180
  1999-10-01  80.547
  2000-01-01  81.163
  2000-04-01  81.623
  2000-07-01  82.152
  2000-10-01  82.593
  2001-01-01  83.112
  2001-04-01  83.699
  2001-07-01  83.973
  2001-10-01  84.227
  2002-01-01  84.497
  2002-04-01  84.812
  2002-07-01  85.190
  2002-10-01  85.651
  2003-01-01  86.179
  2003-04-01  86.455
  2003-07-01  86.934
  2003-10-01  87.346
  2004-01-01  88.108
  2004-04-01  88.875
  2004-07-01  89.422
  2004-10-01  90.049
  2005-01-01  90.883
  2005-04-01  91.543
  2005-07-01  92.399
  2005-10-01  93.100
  2006-01-01  93.832
  2006-04-01  94.587
  2006-07-01  95.247
  2006-10-01  95.580
  2007-01-01  96.654
  2007-04-01  97.194
  2007-07-01  97.531
  2007-10-01  97.956
  2008-01-01  98.516
  2008-04-01  98.995
  2008-07-01  99.673
  2008-10-01  99.815
  2009-01-01  100.062
  2009-04-01  99.895
  2009-07-01  99.873
  2009-10-01  100.169
  2010-01-01  100.522
  2010-04-01  100.968
  2010-07-01  101.429
  2010-10-01  101.949
  2011-01-01  102.399
  2011-04-01  103.145
  2011-07-01  103.768
  2011-10-01  103.917
  2012-01-01  104.466
  2012-04-01  104.943
  2012-07-01  105.508
  2012-10-01  105.935
  2013-01-01  106.363
  2013-04-01  106.623
  2013-07-01  107.128
  2013-10-01  107.589
  2014-01-01  108.009
  2014-04-01  108.606
  2014-07-01  109.044
  2014-10-01  109.067
  2015-01-01  109.099
  2015-04-01  109.650
  
  
      Monthly Data    Monthly datapoint
  1999-01-01  76.841
  1999-02-01  79.863
  1999-03-01  81.245
  1999-04-01  78.911
  </code></pre>