29
0
0.01
0.02
0.03
0.04
0.05
0 10 20 30 40 50 60 70 80
Proportion
Age (years)
Figure 1: Proportion of individuals who consumed gamebird meat
during a 4-day diet diary survey conducted as part of the UK
National Diet and Nutrition Survey in the years 2008/09 - 2011/12
in relation to age. Each symbol represents the proportion for a group of
individuals in an age class that included at least 200 subjects. The thick
curve shows the asymptotic relationship Pg= exp(-3.459-1.668 exp(-0.073
Age)) fitted to the disaggregated data by a maximum-likelihood method.
The thin curves show bootstrap 95% confidence limits. Results are shown
for both sexes combined because there was no indication of a significant
difference between the sexes.
We next multiplied the number of people estimated to be in
each year class of age in the UK (in mid-2013, from Office of
National Statistics 2014) by the estimated proportion of people
consuming gamebird meat for that age class from the analysis
reported above. Uncertainty in these estimates of proportions
was taken into account by the bootstrap method, but UK
population totals were taken to have been estimated without
error. The total number of people estimated to consume
gamebird meat in a typical 4-day period was 1,613,341 (95%
C.L. 1,293,414 – 1,931,975), which represents 2.52% of the UK
population (95% C.L. 2.02 – 3.01). Equivalent estimates were
made for sub-groups based on age. The estimated number of
children up to the age of 8.0 years that ate gamebird meat is
49,576 (95% C.L. 29,083 – 87,870). The estimated number of
children between 8.0 and 18.0 years that ate gamebird meat is
119,780 (95% C.L. 77,530 – 178,574). The estimated number of
adults that ate gamebird meat is 1,443,984 (95% C.L. 1,091,320
– 1,741,397). It should be noted that these are estimates of
numbers of people eating gamebird meat in a typical four day
period. They are likely to be representative of the situation
for any time of year because proportions of people eating
gamebirdmeat have previously been found to be similar within
and outside the shooting season (Taylor et al. 2014). However,
the numbers of people eating gamebird meat over a longer
period, such as a year, would be larger than this unless people
are completely consistent from one 4-day period to another
in whether they eat game or not. Hence, these estimates are
minimum numbers of consumers of gamebird meat.
We analysed the NDNS data on the mean quantity of gamebird
meat eaten per day using polynomial ordinary least squares
regression of log-transformed values. This analysis included
data only from the 87 subjects who consumed gamebird
meat. We fitted the first-, second-, third-, fourth- and fifth
order polynomial regressions on the age class midpoint in
years. In none of these regression models did the effect of
age on daily gamebird meat consumption rate approach
statistical significance (P always > 0.50). Similarly, the effect of
sex did not approach statistical significance in any model (P
always ≈ 0.50). Visual inspection of the data (Figure 2) similarly
confirmed no sign of consistent effects of age or sex. We
therefore used a single log-normal distribution with no effects
of age or sex to describe the distribution of values. We used
bootstrap resampling of the 87 subjects, with replacement,
to obtain confidence intervals of parameter estimates. We
performed 1,000 bootstrap replicates and took the bounds
defined by the central 950 bootstrap estimates to represent
the 95% confidence limits. The mean of the loge-transformed
daily consumption rate in g/d was 2.511 (95% C.L. 2.294
- 2.725), which is equivalent to a geometric mean of 12.3
g/d (95% C.L. 9.9 – 15.3). The standard deviation of the log-
normal distribution was 1.044 (95% C.L. 0.896 – 1.160). The
arithmetic mean daily consumption rate was 19.1 g/d (95%
C.L. 15.5 – 22.6). Although these data derive from 4-day diet
diary periods, the arithmetic mean daily consumption rates for
those who eat gamebird meat are likely to apply to the whole
year, because sampling was representative of the whole year.
We estimated the total mass of gamebird meat eaten per year
by the whole UK population by multiplying the estimated
numbers of consumers by the arithmetic mean amount eaten
per day and the number of days in a year, with uncertainty
in numbers of people and consumption rates accounted for
using the bootstrap method. The total mass of gamebird meat
eaten per year by the whole UK population was estimated to
be 11,232 tonnes (95% C.L. 9,162 – 16,251).
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