Characteristics of studies included in the CLIC pooled analysis of parental exposure to occupational low-frequency magnetic fields (EMF-MF) and risk of childhood leukaemia
| Country, study (years of case accrual) | Cases | Controls | Source of occupational history data | Time period(s) of interest* | Original occupational coding | Occupational conversion tool to ISCO-88 | ||
| Source | N | Source | N | |||||
| Finland (1990–2011) | Finnish Cancer Registry | ALL: 857. AML: 127. | Population register centre. | 3277 | Population census records (1990, 1995, 2000, 2005 and 2010). | Extracted from census records: (1) Census record preceding conception and (2) Census record preceding pregnancy. | ISCO 1988 and ISCO 2008. | Correspondence table ISCO-08 to ISCO-88. |
| France, ADELE (1993–1999) | Hospitals | ALL: 240. AML: 35. | Hospitals (same as cases). | 288 | Self-administered questionnaire, telephone or face-to-face interview. | Extracted from work history (start and end year of each job): (1) main year before conception (defined as the year of the midpoint of the year before conception) and (2) main year of pregnancy (defined as the year of the midpoint of the pregnancy). | ISCO 1988. | |
| France, ESCALE (2003–2004) | Population-based cancer registry (nationwide). | ALL: 641. AML: 97. | Population quotas by age, sex and region (nationwide). | 1681 | Self-administered questionnaire, telephone or face-to-face interview. | 1. During pregnancy†. | ISCO 1968. | Correspondence table ISCO-68 to ISCO-88. |
| Germany, GCCR (1992–1994) | Childhood cancer registry (nationwide). | ALL: 741. AML: 122. | German registries of residents (regional registries with national coverage). | 2457 | Self-administered questionnaire, telephone or face-to-face interview. | (1) At conception and (2) during pregnancy. | German, Bundesagentur für Arbeit. | Correspondence table to ISCO-88 obtained from Federal Statistical Office, Germany. |
| Greece, NARECHEM (1993–1994) | Nationwide hospital cancer registry. | ALL: 140. AML: 13. | Hospital. | 300 | Self-administered questionnaire, telephone or face-to-face interview. | (1) One year before birth and (2) during pregnancy. | ISCO 1988. | |
| Greece, NARECHEM (1996–2011) | Nationwide hospital cancer registry. | ALL: 957. AML: 112. | Hospital. | 1085 | Self-administered questionnaire, telephone or face-to-face interview. | (1) One year before birth and (2) during pregnancy. | ISCO 1968. | Correspondence table ISCO-68 to ISCO-88. |
| Italy, SETIL (1998–2001) | Clinical cancer registry (nationwide). | ALL: 596. AML: 32. | Registry (nationwide). | 1044 | Self-administered questionnaire, telephone or face-to-face interview. | (1) One year before conception and (2) during pregnancy. | ISCO 1968. | Correspondence table ISCO-68 to ISCO-88. |
| New Zealand, NZCCS (1990–1993) | Registries (nationwide) and admission/discharge system. | ALL: 97. AML: 22. | Birth registry (nationwide). | 303 | Self-administered questionnaire, telephone or face-to-face interview. | (1) Two years before birth and (2) during pregnancy. | UK, Standard Occupational Classification 1990. | Correspondence table to ISCO-88 obtained from Office for National Statistics, UK. |
| UK, UKCCS (1991–1996) | Nationwide general practitioners’ registry. | ALL: 1427. AML: 234. | GP registries (nationwide). | 3447 | Self-administered questionnaire, telephone or face-to-face interview. | (1) Around conception and (2) during pregnancy. | UK, Standard Occupational Classification 1990. | Correspondence table to ISCO-88 obtained from Office for National Statistics, UK. |
| USA, COG-E15 (1989–1993) | Children’s Cancer Group clinical trials. | ALL: 1910. | RDD | 1986 | Self-administered questionnaire, telephone or face-to-face interview. | Extracted from work history (start and end month, year of each job): (1) year before conception and (2) during pregnancy. | US, Department of Labour Dictionary of Occupational Titles (4th ed., rev. 1991). | Correspondence tables obtained from the National Crosswalk Center between DOT to 2000 Census codes, and 2000 Census codes to ISCO-88. |
| USA, CCLS (1995–2008) | Hospitals. | ALL : 814. AML : 132. | Birth registry (state wide). | 1224 | Self-administered questionnaire, telephone or face-to-face interview. | Extracted from work history (start and end month, year of each job): (1) year before conception and (2) during pregnancy. | US, Census Occupational Classification Codes 1990. | Correspondence tables obtained from the National Crosswalk Center between 1990 Census to 2000 Census codes, and 2000 Census codes to ISCO-88. |
*Time periods of interest were: (1) around conception for the father and (2) during pregnancy for the mother.
†In France ESCALE, paternal exposure during pregnancy was used as a proxy for exposure at conception as these data were not available.
ADELE, Adele Study; ALL, acute lymphoblastic leukaemia; AML, acute myeloid leukaemia; CCLS, California Childhood Leukemia Study; CLIC, Childhood Leukaemia International Consortium; COG, Children’s Oncology Group; DOT, Dictonary of Occupational Titles; ESCALE, Epidemiologic Study on Childhood Cancer and Leukemia; GCCR, German Childhood Cancer Registry; GP, General Population; ISCO, International Standard Classification of Occupations; NARECHEM, Nationwide Registry for Childhood Haematological Malignancies; NZCCS, New Zealand Childhood Cancer Study; RDD, random digit dialling; SETIL, Studio sulla Eziologia dei Tumori Infantili Linfoemopoietici; UKCCS, United Kingdom Childhood Cancer Study.