MORTALITY:

Nine larynx cancers were observed in the cohort, five of whom had died. Only two of the decedents had any indication of larynx cancer on their death certificate. The nine cases averaged 26 years since first exposure, and averaged age 53 at diagnosis. All were smokers or former smokers.

Person-Years, Observed Larynx Cancers, and US Comparison Larynx Cancer Rates (per 100000)
Years Age Person-Years in Cohort Observed Larynx Cancers US Rate
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79
75-79		 15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
85+		 0
0
7
115
254
448
527
595
554
480
307
177
83
33
6		 0
0
0
0
0
0
2
1
1
0
0
0
0
0
0
0		 0.0
0.1
0.1
0.6
1.4
4.8
9.1
13.5
27.0
36.2
42.2
41.4
39.1
33.2
23.5

QUESTIONS

To illustrate how expected deaths were calculated, the above Table provides data on the person-years for the cohort in the period 1975-1979, as well as the estimated U.S. age-specific and calendar-time-specific larynx cancer rates. Data on the observed larynx cancers during this five-year period, by age at diagnosis, are also presented. For the actual overall calculation in the study, data similar to these were used, but covered the entire period from 1940 to 1986.

After considering the above, try and answer the following questions:

  1. QUESTION 9. Calculate the overall expected number of larynx cancers during the 1975-1979 calendar period, based on the data in the above Table.
    Calculate the standardized rate ratio (observed to expected) during this period. For what variable (confounder) has this rate ratio been standardized?
    Is this an example of indirect or direct standardization?
    Show that the ratio of observed to expected is actually a ratio of two weighted averages of rates.