Table 4

Process of standardisation (rescaling) of pain intensity measures into a common metric

Step 1
  • Non-VAS pain intensity scales will be initially converted into standardised mean differences (SMD), by dividing the between-group differences in means (in each trial), by the pooled SD of the two groups.

  • The SMD expresses the intervention effect in SD units, rather than the original units of measurement.

Step 2
  • Standardisation will be done by multiplying the SMD by the SD of the VAS scale.

  • The SD used here will be the pooled SD obtained from the largest trial where pain intensity was assessed via VAS.

Step 3
  • Standardised data (now presented as a VAS score) will be meta-analysed with data from other trials (ie, those that used VAS or had pain data converted into VAS) to calculate a pooled WMD in VAS scores.

  • VAS, Visual Analogue Scale; WMD, weighted mean difference.