Table 1 Median, minimum and maximum probability of an observation from an ‘in control’ process falling below the lower limit, and above the upper limit, of 95% and 99.8% funnel plot control limits for the SMR using three different methods to calculate the limits

95% control limits

Lower

1-50

0.0184

0

0.0250

0.0325

0.0219

0.3679

0.0186

0

0.0250

>50-100

0.0216

0.0172

0.0251

0.0287

0.0248

0.0351

0.0215

0.0172

0.0250

>100-500

0.0233

0.0194

0.0251

0.0267

0.0248

0.0317

0.0233

0.0194

0.0250

>500-1000

0.0240

0.0225

0.0251

0.0261

0.0249

0.0277

0.0239

0.0224

0.0250

>1000-10000

0.0246

0.0232

0.0250

0.0254

0.0250

0.0269

0.0246

0.0232

0.0250

Upper

1-50

0.0301

0.0203

0.0841

0.0121

0.0003

0.0177

0.0201

0.0052

0.0250

>50-100

0.0280

0.0247

0.0331

0.0166

0.0129

0.0196

0.0220

0.0184

0.0250

>100-500

0.0266

0.0248

0.0307

0.0203

0.0157

0.0225

0.0234

0.0200

0.0250

>500-1000

0.0260

0.0249

0.0275

0.0220

0.0203

0.0232

0.0240

0.0226

0.0250

>1000-10000

0.0254

0.0249

0.0268

0.0238

0.0216

0.0244

0.0246

0.0233

0.0250

99.8% control limits

Lower

1-50

0.0002

0

0.0006

0.0028

0.0016

0.3679

0.0006

0

0.0010

>50-100

0.0005

0.0003

0.0007

0.0017

0.0014

0.0026

0.0008

0.0006

0.0010

>100-500

0.0007

0.0005

0.0009

0.0013

0.0012

0.0020

0.0009

0.0007

0.0010

>500-1000

0.0008

0.0007

0.0009

0.0012

0.0011

0.0013

0.0009

0.0009

0.0010

>1000-10000

0.0009

0.0008

0.0010

0.0011

0.0010

0.0012

0.0010

0.0009

0.0010

Upper

1-50

0.0021

0.0014

0.0133

0.0002

0.0000

0.0004

0.0007

0.0002

0.0010

>50-100

0.0016

0.0013

0.0021

0.0004

0.0002

0.0005

0.0008

0.0007

0.0010

>100-500

0.0013

0.0011

0.0018

0.0006

0.0004

0.0007

0.0009

0.0007

0.0010

>500-1000

0.0011

0.0011

0.0013

0.0007

0.0006

0.0008

0.0009

0.0009

0.0010

>1000-10000

0.0011

0.0010

0.0012

0.0009

0.0007

0.0009

0.0010

0.0009

0.0010