We use self-reported data in our survey, which is both convenient and low cost. However, this implies an element of uncertainty as to whether the data is correct. Questions about food and lifestyle habits are difficult to test due to their character, but for some parts of the questionnaire, we have been able to validate self-reported data.

Borch K B, Ekelund U, Brage S, Lund E.
Criterion validity of a 10-category scale for ranking physical activity in Norwegian women. Int J Behav Nutr Phys Act 2012 9:2.

Veierød M B, et al.
Reproducibility of self-reported melanoma risk factors in a large cohort study of Norwegian women. Melanoma Research 2008 18(1):1-9.

Hjartåker A, Andersen L F, Lund E.
Comparison of diet measures from a food-frequency questionnaire with measures from repeated 24-hour dietary recalls. The Norwegian Women and Cancer Study. Public Health Nutrition 2007, 10: 1094-1103.

Parr C L, Veierød M B, Laake P, Lund E, Hjartåker A.
Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC). Nutr J. 2006;5:4.

Lund E, et al.
External validity in a population-based national prospective study–the Norwegian Women and Cancer Study (NOWAC). Cancer Causes Control. 2003 14(10):1001-8.

Brustad M, Skeie G, Braaten T, Slimani N, Lund E.
Comparison of telephone vs face-to-face interviews in the assessment of dietary intake by the 24 h recall EPIC SOFT program–the Norwegian calibration study. Eur J Clin Nutr. 2003 57(1):107-13.

Lund E, Gram I T.
Response rating according to design of questionnaire. Scand J Soc Med 1998 26(2):154-60.

Hjartåker A, Lund E, Bjerve K S.
Serumphospholipid fatty acid composition and habitual intake of marine foods registered by a comprehensive food frequency questionnaire. Eur J Clin Nutr 1997 51:736-42.