It is a major strength of this study that 87.4% of the eligible adult population participated, suggesting that the participants are fairly representative for the underlying population of Nord Trøndelag county in Norway.
Although no other tested persons in this childcare facility were found to carry ST398, only 24 (40%) of the 60 employees and 8 (4.8%) of the 168 children participated, suggesting the possibility of a reservoir in the facility among those who were not tested.
For example, our anecdotal observation of increased frequency of traffic accidents in 20% of drivers who did not agree to participate, suggested that this subpopulation differed in both psychological profile and probability of traffic accident from subpopulation under the study.
38 40 41 Whatever the reasons for it, the high attrition rate among those participants who agreed to participate suggests that a register based on postal/telephone follow-up will be labour intensive and might fail to engage a significant proportion of the most vulnerable patients.
Nevertheless, the sample size of the study was relatively large and there was no significant difference in maternal age and level of education between participants and those declining to participate, suggesting that the sample was representative of the population from which it was drawn.
There appear to be no important gender or age differences between the interviewed twin sample and the twins refusing to participate, suggesting the final twin sample is not biased according to selective participation.
The fact that many came from outside the shire to participate suggests so.
Moreover, the fact that only 30% of patients eligible for inclusion in the present study consented to participate suggests that the number of illicit drug users attending hospital emergency departments in Spain may be higher than was previously estimated.
