Homework 2

# Homework 2 - Homework#2 1 a This is a case-control study...

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Homework #2 1. a) This is a case-control study that examines the potential causality between SHS exposure during pregnancy and low birth weight of the infants. The outcome of interest is maternal SHS. The exposure of interest is low birth weight. The cases are the mothers of infant that weigh less than 2500g. The controls are the mothers of infants that weigh more than 3000g. b) Low Birth Weight Yes No Totals Maternal SHS during pregnancy Yes 172 100 272 No 183 479 662 Totals 355 579 934 Odds Ratio (OR)= a.d/b.c= (172)(479)/(183)(100)= 4.5 The odds ratio indicates that infants whose mothers were exposed to SHS during pregnancy are 4.5 times as likely to have low birth weight (<2500g.) c) f= 0.30 PAR%= {f(OR-1)/[f(OR-1)]+1} x 100 = {0.30(3.5)/[(0.30)(3.5)+1]} x 100 = 51.2% We could hope to eliminate 51.2% of low birth weight from the entire population if we could reduce maternal SHS exposure during pregnancy. 2) a) a) No: There is no reference to mortality in the graphs. b) Yes: Each dot represents the number of new cases per year. So it could be said that women “get” less of both diseases than men because every year there are less women than men who are diagnosed. However, it is important to note that the

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answer depends on how “get” is defined (we have assumed that “get” means number of new cases.) c) No: Although each year more men will experience new cases, we do not know what the number of cases was for each group at the beginning of the study. The graphs indicate incidence, not prevalence. d) No: “doing better” is a poor scientific term. Men have experienced greater reduction rates of infection than women over the given time period, but women have overall lower rates of infection. There is no way to determine “better.” e) There is no way to tell. Yes, it has higher rates of infection each year than disease 1, but the effect of the disease must be taken into account. If disease 2 is a common cold and disease 1 is a highly infectious disease with high rates of mortality, disease 1 might be more of a threat. Again, “bigger threat” is a highly subjective term. f) If “more men will be diagnosed with both diseases” is trying to suggest that there are men who are infected with both (2) diseases, then this statement cannot be determined with the given data. If the phrase suggests that there are larger numbers of men who have disease A and larger numbers of men with disease B than there are number of women with disease A and number of women with disease B, then we need to know the population distribution of men to women. However, if we assume a 50/50 split, then number-wise (in the population) there will be more men infected with either disease than women. g)
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Homework 2 - Homework#2 1 a This is a case-control study...

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