Table 4.

Judgment of external validity

Criterion	Routine data analysis	Impact on external validity	Oral health survey	Impact on external validity
Representativity	Sample representative for a small study population	Negative	Representative sample	Positive
	Sample representative for a large study population (e.g., nationwide insurance data)	Negative to positive (depending on population characteristics)	Nonrepresentative sample	Negative
Response/selection	Very high coverage rate, no selection	Positive	Low response rate	Negative
			High response rate	Positive
Blinding (subjects)	Health system data − no direct connection to subjects	Positive	Subjects are informed about study aim − healthy subjects possibly more attracted	Negative
Statistical adjustments	Adjustments possible (e.g., of age and gender)	Positive	Nonresponse analysis	Positive
			No nonresponse analysis	Negative
Potential replication	Replication easily possible	Positive	Possible, but more difficult	Negative

Variable: caries experience of 12-year-olds. Routine data analysis versus oral health survey. No claim to completeness.