Moreover, although the total sample size is over 4000, cell sizes can be very small because psychiatric problems, such as ADHD, substance use, and collisions have low prevalence; small cell sizes and large CIs suggest a low level of precision, as indicated in some of the variables in Table 3.
The sample was relatively small, involving only three hospitals and 1023 nurses in North China, therefore the number of outcome events in some subgroups, especially chronic daily headache with low prevalence, is small.
Due to its low prevalence and small size of its target population, the PMTCT program in Honduras has a number of characteristics making it different from both those in high-prevalence African countries and India.
Different liquids, including sodium sulfite and glycerin solutions, are used; the former as an electrolyte solution favors the formation and prevalence of smaller bubbles, thus for examining the bubble-size effect; the latter leads to a smaller increase in the local pressure gradient due to viscous action.
It is speculated that the prevalence of smaller Spigelian hernias could be higher than believed today.
The prevalence was smaller among the children who used pacifier until 2 years of age.
Regional differences in prevalence were smaller in 2005.
The subgroup of studies with larger sample size (n > 200) had a lower prevalence than smaller studies (7.2% vs. 13.6%).
Analysis of patient level postcode information, not available for this study, would allow estimates of smoking prevalence for smaller geographical areas to be made.
Although if this were the primary reason for the higher prevalence, a smaller difference between sites consistent with previous studies of genital HPV would be expected [ 20, 21].
