Table 1 Average impact factors of articles written by authors from six countries from 2000 to 2011

2000

2.911

2.556

2.780

2.369

2.312

2.561

2001

2.869

2.640

2.507

2.352

2.350

2.186

2002

2.950

2.522

2.230

2.340

2.545

2.383

2003

2.936

2.438

2.571

2.425

2.587

2.541

2004

2.891

2.501

2.594

2.548

2.547

2.450

2005

2.857

2.401

2.620

2.473

2.531

2.380

2006

2.864

2.393

2.563

2.705

2.664

2.608

2007

2.829

2.323

2.391

2.704

2.694

2.486

2008

2.798

2.428

2.592

2.637

2.605

2.446

2009

2.794

2.449

2.630

2.627

2.709

2.490

2010

2.756

2.523

2.347

2.695

2.686

2.490

2011

2.874

2.473

2.554

2.608

2.564

2.444

Total

2.856

2.460

2.525

2.567

2.569

2.471