Wang 1999.

Methods	FLUOROSIS STUDY Country of study: China Geographic location: Xindiliang Village (high F), Shiligetu Village (lower F) Year of study: 1999 Year of change in fluoridation status: NA Study design: cross sectional study
Participants	Inclusion criteria: not stated Exclusion criteria: not stated Other sources of fluoride: not stated Social class: not stated Ethnicity: not stated Residential history: not stated Other confounding factors: not stated
Interventions	All natural fluoridation Group 1: 1.3 ppm Group 2: 2‐4 ppm
Outcomes	Dental fluorosis and skeletal fluorosis (3 grade classification for both) Age at assessment: all ages
Funding	Japan International Cooperation Agency
Notes	Removal of fluoride from the water in these areas was attempted in the 1980s but failed to be applied continuously
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Unclear risk	Households in the villages of study were arbitrarily chosen so that 25% were included in the study
Confounding	High risk	Did not account for the use of fluoride from other sources
Blinding of outcome assessment (detection bias) All outcomes	High risk	Insufficient information
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data presented for all participants
Selective reporting (reporting bias)	Low risk	Outcome of interest presented
Other bias	High risk	There was no mention of examiner calibration