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Table 1 Validity criteria used to score studies

From: Association of Down's syndrome and water fluoride level: a systematic review of the evidence

Prospective Was the study prospective? Was it planned and started prior to the outcome of interest
  occurring? Score = 1 or 0
Study Design The study design hierarchy for this review = cohort > before-after > ecological > cross-
  sectional. Scores ranged from 0.25–1, with cohort = 1, cross-sectional = 0.25
Fluoride Measurement Was the Fluoride level reliably measured? Scores range between 0–1.
Confounding Factors Were confounding factors addressed (measured)? Scores range between 0–1, with 3 or more
  factors measured = 1.
Control for Confounding Was there adjustment for the possible effect of confounding factors in the analysis or study
  design? Scores range between 0–1, with stratification by age and sex = 0.5, other types of
  analysis (e.g. regression) = 1.
Blinding Were those measuring outcomes and exposures blind to the exposure/outcome status of the
  person being assessed? Score = 0 or 1
Baseline Survey Was there a baseline survey at the point of initiation or discontinuation of water fluoridation?
  Score = 0 or 1
Follow-Up Was the study conducted an adequate time after the initiation or discontinuation of water
  fluoridation to assess effects (5 years)? Score = 0 or 1