Loss to follow-up is problematic in most cohort studies and often leads to bias. Although guidelines suggest acceptable follow-up rates, the authors are unaware of studies that test the validity of these recommendations. The objective of this study was to determine whether the recommended follow-up thresholds of 60-80% are associated with biased effects in cohort studies. A simulation study was conducted using 1000 computer replications of a cohort of 500 observations. The logistic regression model included a binary exposure and three confounders. Varied correlation structures of the data represented various levels of confounding. Differing levels of loss to follow-up were generated through three mechanisms: missing completely at random (MCAR), missing at random (MAR) and missing not at random (MNAR). The authors found no important bias with levels of loss that varied from 5 to 60% when loss to follow-up was related to MCAR or MAR mechanisms. However, when observations were lost to follow-up based on a MNAR mechanism, the authors found seriously biased estimates of the odds ratios with low levels of loss to follow-up. Loss to follow-up in cohort studies rarely occurs randomly. Therefore, when planning a cohort study, one should assume that loss to follow-up is MNAR and attempt to achieve the maximum follow-up rate possible.

The MutY human homologue (MYH) gene encodes a member of the base excision repair pathway that is involved in repairing oxidative damage to DNA. Two germline MYH gene mutations that result in Myh proteins containing amino acid substitutions Y165C and G382D (hereafter called the Y165C and G382D mutations) are associated with adenomatous poly-posis and colorectal cancer among patients from several European poly-posis registries. We used a population-based series of 1238 colorectal cancer patients and 1255 healthy control subjects from Ontario, Canada, to examine the risk of colorectal cancer among biallelic and monoallelic germline MYH Y165C and G382D mutation carriers. The entire MYH gene coding region was screened in all MYH Y165C and G382D mutation carriers. Compared with noncarriers, biallelic and monoallelic germline MYH gene mutation carriers had an increased risk of colorectal cancer and were more likely to have first-or second-degree relatives with colorectal cancer (relative risk = 1.54, 95% confidence interval = 1.10 to 2.16). The increased risk of colorectal cancer in biallelic and monoallelic MYH gene mutation carriers was not consistently associated with the development of multiple adenomatous polyps. Loss of heterozygosity in at least one of four loci in MYH was detected in eight (47%) of 17 colorectal tumors from monoallelic MYH gene mutation carriers but in only two (20%) of 10 colorectal tumors from biallelic MYH gene mutation carriers. These two MYH gene mutations may account for a substantial fraction of hereditary colorectal cancer.

Background: There is growing evidence that adolescent workers are at greater risk for work injury. Aims: To investigate the severity of work injuries across age groups. Methods: Workers' compensation records were used to examine work related injuries among adolescents (15-19 years old), young adults (20-24 years old), and adults (25+ years old) between 1993 and 2000. The incidence of compensated injuries was calculated for each age group and compared by gender, industry, and type of injury. The presence and degree of permanent impairment in each age group was also examined. Results: For males, adolescents and young adults had higher claim rates than adults. For females, adults had the highest claim rates and young adults the lowest. Rates of permanent impairment indicated that age was positively associated with severity of injury. Conclusions: Indicators of health consequences, in particular presence of permanent impairment, provide preliminary evidence that compensated work injuries sustained by youth are not as serious as injuries sustained by adults. Nevertheless, there was evidence that some young workers sustain injuries that have long term consequences. Documenting the consequences of the injuries that young workers sustain has implications for secondary prevention efforts and health services policy.