After adjusting for
confounding factors such as age, education and occupational status, the researchers found that not only was there a 30 % increased risk
of any arrhythmia with the highest
number of races completed and the fastest finishing time, but also the risk increased
by 10 % between each category for the
number of races completed, i.e. there was a 10 % increased risk from the least exposed group
of participants (those who completed only one race) to the next group (two races), another 10 % increase in risk to the next group (three - four races) and another 10 % to the most exposed group (five or more races).
«The discordant twin design minimizes a
number of potentially
confounding factors that may explain the association between childhood verbal ability and subsequent alcohol use
by «controlling» for differences on variables [such as] socioeconomic differences or family
factors that, if excluded, could cloud the interpretation
of findings.»