The Home Office undertakes occasional research which covers regional variations in conviction rates.
The Home Office-commissioned study “A gap or a chasm? Attrition in reported rape cases” (Kelly, Lovett and Regan, 2005) focused on the general process by which rape cases are “lost” from the criminal justice system but did include a statistical analysis of conviction rates by police force area using routinely collected administrative data.
The Home Office is currently concluding a study of rape attrition in eight force areas in England and Wales which is more explicitly aimed at improving our understanding as to why conviction (and detection) rates vary across the country. This study will be published in 2007.