As we have no information about paternal occupation before or after a child's birth was registered, the occupation (and hence exposure) may have been different and exposure misclassification may have arisen as a result; however, this applies equally to cases and controls.
The occupation held longest was registered as the occupation for that participant.
One in every ten did not register an occupation (3.7% 751/20,639 missing data).
This limits the results as concerns women, but since only 47.5% vs 48.5% had an occupation registered, it was not fruitful to analyze further.
All available information in the included tramadol cases was registered: age, sex, occupation, marital status, educational status, concomitant medication, prescribed and ingested doses of tramadol, duration of tramadol abuse, and other important information.
Demographic data, including the identification number, sex, age, occupation, registered residence, current address, as well as results of mycobacterial smears, symptoms and treatment history were obtained from medical records provided by Chaoyang Centre for Disease Control and Prevention, Beijing.
The attribute items in the dataset included sex, age, occupation, registered residence, workplace or current residence, onset location, reporting units, onset time, hospitalization time, diagnosis time, and other information, which was separate information collected from the SARS case.
Not having an occupation could be of importance in terms of being one reason to change one's place of residence; a larger proportion of men with no occupation registered was found in the group that had changed their county of residence (19.9% vs 13.8%).
Human occupation was registered in the last two phases, with settlements of hunter-gatherer groups, sambaquis builders, and Meridional Jê and Guarani groups.
The questionnaire registered socio-demographic characteristics, occupation of parents, and food habits.
