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. 2019 Dec 12;2019(12):CD011927. doi: 10.1002/14651858.CD011927.pub2

3. Planned subgroup analysis and investigation of heterogeneity.

Planned subgroup analysis and investigation of heterogeneity
We planned to investigate heterogeneity and perform subgroup analyses considering the following factors.

  1. TENS level of stimulation (subsensory, sensory, motor, and noxious)

  2. Stimulation parameters (frequency, intensity, and pulse duration)

  3. Gender

  4. Age

  5. Duration of the treatment

  6. Classification of neck pain (grade I, II and III)

  7. Type of neck pain (e.g. non‐specific versus whiplash versus headache versus 'other')

  8. Period of follow‐up (immediately post‐treatment, short‐term, intermediate‐term and long‐term)


In the presence of two or more subgroups, we planned to considered the I2 statistic to assess the heterogeneity among them. This statistic describes the percentage of the variability in effect estimates from the different subgroups that is due to genuine subgroup differences rather than sampling error (chance). We considered an I2 statistic of 50% or higher as suggestive of substantial heterogeneity among subgroups.

TENS: transcutaneous electrical nerve stimulation