Field substitution of nonresponders can maintain sample size and structure without altering survey estimates-the experience of the Italian behavioral risk factors surveillance system (PASSI).
OBJECTIVE
Field substitution of nonrespondents can be used to maintain the planned sample size and structure in surveys but may introduce additional bias. Sample weighting is suggested as the preferable alternative; however, limited empirical evidence exists comparing the two methods. We wanted to assess the impact of substitution on surveillance results using data from Progressi delle Aziende Sanitarie per la Salute in Italia-Progress by Local Health Units towards a Healthier Italy (PASSI).


METHODS
PASSI is conducted by Local Health Units (LHUs) through telephone interviews of stratified random samples of residents. Nonrespondents are replaced with substitutes randomly preselected in the same LHU stratum. We compared the weighted estimates obtained in the original PASSI sample (used as a reference) and in the substitutes' sample. The differences were evaluated using a Wald test.


RESULTS
In 2011, 50,697 units were selected: 37,252 were from the original sample and 13,445 were substitutes; 37,162 persons were interviewed. The initially planned size and demographic composition were restored. No significant differences in the estimates between the original and the substitutes' sample were found.


CONCLUSIONS
In our experience, field substitution is an acceptable method for dealing with nonresponse, maintaining the characteristics of the original sample without affecting the results. This evidence can support appropriate decisions about planning and implementing a surveillance system.
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Sandro
S
Baldissera
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy. Electronic address: gianluigi.ferrante@iss.it.
Gianluigi
G
Ferrante
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Elisa
E
Quarchioni
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Valentina
V
Minardi
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Valentina
V
Possenti
Department of Public Health, Modena, Italy.
Giuliano
G
Carrozzi
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Maria
M
Masocco
National Centre of Epidemiology, Surveillance and Health Promotion, National Institute of Public Health, Rome, Italy.
Stefania
S
Salmaso
D000328:Adult; D040343:Behavioral Risk Factor Surveillance System; D015982:Bias; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007558:Italy; D008297:Male; D008875:Middle Aged; D036301:Qualitative Research; D012107:Research Design; D018401:Sample Size; D012494:Sampling Studies; D055815:Young Adult
Data collection; Italy; Public Health Surveillance; Research design