Date:         Sat, 28 Nov 2009 08:42:28 -0800
Reply-To:     "Kenneth M. Lin" <kenneth_m_lin@sbcglobal.net>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Kenneth M. Lin" <kenneth_m_lin@SBCGLOBAL.NET>
Subject:      Re: Correlation help
Comments: To: sas-l@uga.edu
In-Reply-To:  <726074a7-7543-49a7-8bd0-525207942e0a@o9g2000vbj.googlegroups.com>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
              reply-type=original

Where did you get the value for "gas consumption"?  Is it for household gas
usage and not just the cylinders?  Then the gas usage would automatically
increase during the winter time for heating but cylinder usage might
decrease because people usually cook outdoor when the weather is good.
Also, is this a nationwide values?

"SD" <saurabhkdas@gmail.com> wrote in message
news:726074a7-7543-49a7-8bd0-525207942e0a@o9g2000vbj.googlegroups.com...
> Hello everyone,
>
> I am not a stats guy, however I have a project I need to finish. The
> null hypothesis  is increase in sales of cooking gas cylinders means
> increase consumption/usage  of cooking gas .
>
> I did a correlation  between two variables "cooking gas cylinders" and
> gas consumption.  I have monthly data points from 2006 to 2009 Sep.
> And I am getting negative correlation. what should be my next
> approach , because in my mind I know that atleast it should not be
> negatively correlated. Again 40 odd data points is too less to do this
> kind of exercise. Any ideas on how go about this, and may be sales of
> gas cylinders may not be the real cause of increase of usage of gas,
> but certainly not negatively correlated. Just to add, there are 3
> types of gas cylinders, the ones made in 2006 had a different
> technology, while the ones made in 2009 are of different technology, I
> did do an overall sales vs overall gas usage , and again new
> technology gas sales vs gas usage from new technology cylinders, again
> negative correlation.
>
> Now suppose people are buying 2 cylinder, or tri cylinder , that does
> not mean they are going to use all of them together,  So I tried to
> factor in a lag, of 1 to 6  months, again negative correlation.
>
> dataset looked like
>
> months cylindersales gas_usage_no_lag      lag1        lag2      lag3
> jan06      10                   45litres
> -              -          -
> feb06       20                  75 litres              45litres
> -         -
> mar06      15                  67 litres                75
> litres       45litres       -
>
> etc
>
> Just want to know if my approach is correct and any quick help would
> be greatly appreciated.
>
> thanks in advance
> SD