2. The ages of the children at the time they underwent intestinal investigation is given in Table 1. Assume that all the children had their MMR immunisation at age 1 year. On average how much time elapsed between the MMR and investigation (calculate this)
KM Madsen, A Hviid, M Vestergaard, D Schendel, J Wohlfahrt, P Thorsen, J Olsen, M Melbye. A Population-Based Study of Measles, Mumps and Rubella Vaccination and Autism. N England J Med, 2002 347: 1477-1482
Answer: Unlike case control study, cohort study gives the freedom to include samples both from affected (diseased) and unaffected (without disease i.e. control) pool. We can compare the effect of a specific phenomenon on both the population types simultaneously and draw inference accordingly through cohort study. Although, the cohort study is more expensive but, the validation of information on exposure is complete and always provide enough information on incidence rates of the diseases. Cohort study is a rare exposure and minimise bias in the exposure determination. But sometimes the diseases are rare. In that situation case-control study is a must which Examine multiple etiologic factors for a single disease.
Answer: Information from the Danish Civil Registration System was used to identify the link from the accompanying adult to child. Thus, 98.5 percent of children were identified with the use of child's civil registry number or the civil-registry number of father or mother and the age of the child at the time of vaccination on the basis of additional information The remaining 1.5 percent of children were identified on the basis of additional information from Danish Civil Registration System on other relatives and information on the address at the time of vaccination. So far as the diagnosis is considered, all diagnosis were based on standard criteria like International Classification of Diseases, 10th Revision (ICD-10) which is similar to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) with regard to autism.
e) Is this method of case ascertainment likely to identify all cases of autism in the cohort If some children with