Sampling procedures and sample representativeness in a national telephone survey: a Portuguese example

Area of Science:

• Public Health
• Survey Methodology
• Epidemiology

Background:

• National telephone surveys are crucial for public health surveillance.
• Assessing sampling procedures and representativeness is vital for data validity.
• Previous studies highlight challenges in achieving representative samples via telephone.

Purpose of the Study:

• To evaluate the yielding of sampling procedures in a Portuguese national telephone survey.
• To assess the representativeness of the obtained sample compared to the general population.
• To determine the impact of different contact schedules on survey outcomes.

Main Methods:

• Utilized the Portuguese telephone book (2007/2008) as the sampling frame for individuals over 39 years old (n=1,934).
• Quantified interview time and unsuccessful contact durations, comparing yield rates across different contact schedules.
• Compared demographic and health characteristics of the survey participants with the broader Portuguese population.

Main Results:

• A 40.4% refusal rate was observed, with higher refusals on Saturdays and during evening calls.
• Evening interviews resulted in a higher proportion of men and active workers.
• The final sample overrepresented women, the elderly (>59 years), and more educated individuals compared to the Portuguese population.
• However, sex- and age-specific estimates for smoking and obesity were comparable to national data.

Conclusions:

• Telephone survey sampling in Portugal faces challenges, including significant refusal rates.
• Despite these difficulties, the employed strategy demonstrated potential for generating unbiased estimates for critical health indicators.
• This suggests that telephone surveys can remain a valuable tool for public health research when carefully implemented and analyzed.