Key findings from the 2009 New Zealand ... - Ministry of Health

Non-sampling errors
Non-sampling errors may occur in any enumeration, regardless of whether it is a
sample or a full enumeration. Possible non-sampling errors include coverage errors,
response bias and measurement errors. Although these elements cannot be measured,
it is useful to be aware of them when interpreting the results of the survey.
Considerable effort has been made to reduce non-sampling errors by carefully
designing and testing the survey, questionnaire and processes, and by ensuring quality
control of procedures and data.
In the 2009 NZTUS, coverage errors may have occurred; for example, because a small
proportion of the population could not be covered by the survey (including people living
in meshblocks with fewer than nine occupied dwellings, and people not living in the
North Island, South Island or Waiheke Island). Response bias may have occurred if
there was differential non-response; that is, if the survey was less likely to be answered
by certain people, such as a certain population group (eg, young males) or people who
were not often home. The interview introduction was an important part of trying to
ensure that people take part in the survey.
Measurement error might also have occurred in this survey. Many of the analyses in
this report used self-reported information, which may have resulted in some
inaccuracies. Measurement errors include recall error (eg, mistakes made when
respondents recall how often they have done something over the last 12 months),
under- and over-reporting (which may be influenced by the respondent’s perception of
what is socially desirable) and item non-response (if the respondent chooses not to
answer certain questions).
Time trend comparisons
Where possible, and relevant, time trend comparisons are made between the 2009
NZTUS, 2008 NZTUS, 2006 NZTUS and the 2006/07 New Zealand Health Survey
(NZHS). 4
Time trend analyses have been conducted for the total population by sex and for Māori
by sex. Comparisons with earlier survey data for other ethnic groups have not been
presented due to the limited space available. Where the sample size allows, time trend
analyses for other ethnic groups will be presented in online web tables.
Due to differences in how data have been collected and presented over time, the results
presented in this report may be slightly different from those in earlier publications and
caution should be used when comparing data. Direct comparisons with data that are
not included in the time trend analysis in this report need to be treated with caution.
In particular, the following should be noted.
The 2006 NZTUS questionnaire comprised two sections: one for those aged 15–19
years and the other for those aged 20–64 years. There were some differences in the
4
To ensure as much comparability as possible, the 2006/07 New Zealand Heath Survey data set was
re-weighted and limited to 15–64-year-olds.
6 Tobacco Use in New Zealand