First, sociodemographic differences between the selected telephone and face-to-face samples could have influenced item response.
* p < 0.01 ** p < 0.001 Statistically significantly different from telephone survey The associations of current SEP variables with missing data on parents' highest education level were similar for the telephone and face-to-face samples and the EWP subsample.
All participants were visited at their homes, where they underwent face to face interviews, blood sampling, electrocardiography, and functional tests.
36 Initial designs using parameter estimates from current literature, where available, will be piloted face to face in a sample of 20 respondents, and preliminary models estimated.
Interview (phone-based or face-to-face, sample of 11): average response rate of 59%%, standard deviation of 22.3 %.
A subsample of respondents in the face-to-face sample who owned a telephone that was listed in the EWP (n = 2206) was also compared to the telephone interview sample.
Thin samples for TEM were prepared in cross section following a standard procedure after gluing the two samples together face to face: a 500- μm-thick lamella was cut out using a diamond saw, subsequently thinned to approximately 15- μm thickness by mechanical polishing, glued on a copper support ring, and argon ion-milled to electron transparency.
18 19 The interview sample had face to face interviews at ages 21, 23, 28, 30, 35, 41, and 50 years for women; men were one year younger at all interviews (fig 1).
Theoretical sampling added 12 face to face interviews and 10 telephone interviews to the data.
All household samples were approached for face to face interviews during personal visits by trained enumerators.
