Description of variables in the study, Federal Road Safety Corps, Kaduna Sector Command, Nigeria, June–July, 2015
| Variable | Description | Type of data |
| Independent variables | ||
| Sex | This was the sex of the study participants, categorised as either men or women | Nominal |
| Age | This variable ascertained the age of participants on their last birthday. It was categorised to enhance anonymity from 18 years, which is the age definition of commencement of adulthood, to ≥50 years, which marks the age before retirement from Nigerian Civil Service at 60 years. The categories included: 18–29 years; 30–39 years; 40–49 years;≥50 years | Ordinal |
| Duration of service | This variable elicited how long a respondent had been in service with the Federal Road Safety Corps. It was categorised into: 6 months–2 years (probation period in the civil service); 3–10 years; 11–19 years; and≥20 years (close to retirement by service year at 35 years). | Ordinal |
| Cadre | This ascertained the official class of participant based on position and seniority in office. There were two major categories: officers and marshals, with the latter sub-categorised into marshal inspectorate and field marshal assistant in descending order. It also signified educational qualification order with the least educated being the field marshal assistant. | Nominal/Ordinal |
| Risk perception | This ascertained the level of perception of occupational risk of exposure to hepatitis B virus by respondents. It was initially categorised as: no risk of exposure, low risk of exposure, moderate risk of exposure, high risk of exposure and I don’t know. This was later dichotomised for further analysis by merging the ‘I don’t know’ group with the ‘no risk’ group to form a ‘no risk perceived’ category with the rest forming the ‘risk perceived’ category. | Nominal/Ordinal |
| Hepatitis B virus knowledge score | This variable sought to estimate the level of knowledge of basic information on hepatitis B virus. It includes questions on hepatitis B virus awareness, seriousness compared with HIV and route of transmission. For each participant, the number of questions answered correctly was noted as the score (see scoring table in online supplementary appendix B). | Continuous |
| Hepatitis B vaccination knowledge score | This measured the level of basic knowledge of hepatitis B vaccination among participants. It comprised questions on hepatitis B vaccination awareness, effectiveness, recommended full dosage and duration of protection from full dose vaccination. For each participant, the number of questions answered correctly was noted as the score (see online supplementary appendix B). | Continuous |
| Dependent variable | ||
| Hepatitis B vaccination status | Information was elicited on whether the participant had ever received hepatitis B vaccination and the number of doses received. Descriptive analysis was done using these data. Dichotomisation of data was also done for logistic regression analysis. As only those with ≥3 doses of hepatitis B vaccination uptake are considered fully protected,11 those with ≥3 doses were labelled ‘vaccinated’ and the rest ‘not vaccinated’. This was noted as the hepatitis B vaccination status of each participant. | Nominal |