Participating households are chosen from a number of randomly selected Census meshblocks. Each selected household is allocated two consecutive travel days to be surveyed. Surveying takes place on every day of the year.
Over a five to seven year cycle, every household in the selected meshblock will be invited to participate in the survey. Once this happens, new meshblocks will be selected for sampling.
Some time before the designated travel days, the household is sent an introductory letter outlining the survey and advising that a surveyor will call. During the week prior to the travel days, an interviewer visits the home, and with the agreement of residents explains the survey and a pamphlet about the survey (PDF, v 7.0 3.14MB). and leaves a Memory jogger (PDF, v 7.0 143KB) for each member of the household member in which respondents can nothe their travel on the selected days. People who drive a truck, bus or taxi for a living complete a Professional Driver memory jogger (PDF v7.0, 148KB). Basic household information is also collected at this interview.
As soon as possible after the travel days, the interviewer returns and conducts a personal interview with each household member, during which his/ her travel details, accident history, alcohol consumption and other personal data are recorded.
Between 2003/04 and 2007/08 (inclusive), 2,200 households were invited to participate each year. From 2008/09 onwards, approximately 4,600 households are invited to take part in the survey each year. In addition, Environment Canterbury, Christchurch City, Waimakariri and Selwyn Districts have contributed funding for an expanded sample in those areas during the 2008/09 and 2009/10 years.
Data Entry and validation
Survey data are entered into an access database using a laptop computer, at the time of interview. Paper questionnaires are provided for situations where use of the computerised form is not practicable, and the results are entered into the database later by the interviewer.
Data validation checks (including on the spot verification of street names) are incorporated into the database, giving rapid feedback and enabling early correction of errors.
Calculating trip distances
Trip distances for cycle and motor vehicle trips are calculated from the origin and destination addresses provided by the respondents. Critchlow Ltd (external link) were contracted to generate automated map coordinates for each address and then to calculate distance based on the fastest route between the origin and destination addresses, or via a specified intermediate address if one was provided.
For further technical detail see Detailed survey information.