Article history: Received 30 April 2009 Received in revised form 12 January 2010 Accepted 20 January 2010 Available online 1 February 2010 JEL classification: D44 D81

Article history: Received 7 July 2010 Received in revised form 20 January 2011 Accepted 24 January 2011 Available online 2 February 2011 Communicated by A.P. Fordy

Article history: Received 20 November 2013 Received in revised form 24 January 2014 Accepted 29 January 2014 Available online 5 April 2014

Article history: Received 7 August 2009 Received in revised form 4 December 2009 Accepted 20 January 2010 Available online 28 January 2010

Article history: Received 28 July 2008 Received in revised form 3 August 2009 Accepted 11 January 2010 Available online 20 January 2010

Article history: Received 14 Novemberr 2013 Received in revised form 20 January 2014 Accepted 23 January 2014 Available online 25 February 2014

Article history: Received 8 September 2014 Received in revised form 20 January 2015 Accepted 28 January 2015 Available online 3 February 2015

Article history: Received 22 October 2013 Received in revised form 14 January 2014 Accepted 20 January 2014 Available online 15 February 2014

18 19 20 21 22 23 24 Article history: Received 9 December 2013 Received in revised form 10 January 2014 Accepted 10 January 2014 Available online xxxx

Article history: Received 20 September 2010 Received in revised form 3 January 2012 Accepted 13 January 2012 Available online 1 February 2012