POSTAL OR WEB-BASED? POPULATION REPRESENTATIVENESS IN HEALTH SURVEY SETTINGS

Purpose: In population health surveys, national representativeness is of the utmost importance. Due to increased availability of online computers and increased computer literacy, the current gold standard of using postal surveys is challenged. The objective of this study was to compare the population representativeness of web-based and postal survey modes in a health survey setting where national representativeness is vital.

Method: We developed postal and web variants of a health valuation survey with intended to maximize representativeness in the adult Norwegian population. The postal version was mailed to a random sample of 5000 persons over the age of 18 drawn from the Norwegian Population Registry. For the web-survey, we invited 1936 respondents from the market research company Synovate’s standing panel of willing survey participants. We compared the two surveys in terms of distribution of respondents’ demographic characteristics and EQ-5D self-ratings.

Result: 4899 (postal) and 1936 (web) respondents were reached, of whom 1276 (26%) and 1003 (50,2%), respectively, submitted complete forms. Characteristics are listed in the table:

Table: Demographics and EQ-5D self-ratings, percentages
Demographics			Postal		Web		Norway		EQ-5D			Postal		Web
Age, years									Across dimensions
	18-29		13,40		10,17		20,02			No problems		49,4		43,0
	30-39		14,34		13,96		17,78			Any problems		50,6		57,0
	40-49		17,63		20,04		18,71			Any extreme		5,0		7,6
	50-59		19,20		22,33		16,29
	60-69		17,08		26,12		13,65		Some problems
	70-79		11,29		6,48		7,74			Mobility		15,2		15,4
	80+		7,05		0,90		5,81			Self-care		3,0		2,3
										Usual activities		15,9		19,0
Edu, years										Pain/discomfort		39,9		44,3
	<=9		13,40		10,17		29,80			Anxiety/depression		19,9		20,9
	9-12		31,97		34,00		42,90
	13-15		19,20		22,33		20,80		Extreme problems
	16+		17,08		26,12		6,50			Mobility		0,0		0,1
										Self-care		0,2		0,0
Sex										Usual activities		1,1		1,4
	Male		48,20		48,16		49,57			Pain/discomfort		3,6		6,0
	Female		51,80		51,84		50,43			Anxiety/depression		1,1		1,3

Conclusion: The web survey outperformed the postal in terms of demographic representativeness, particularly for education, albeit with low participation rates over the age of 70. The distributions of reported EQ-5D problems were similar, but web respondents reported more problems, possibly due to lower mean education levels. Severe health problems are likely to be underrepresented.  Web surveys may already be superior to postal surveys in terms of representativeness, and may be recommended for use in studies in countries with widespread access to computers and high levels of computer literacy.