Part 1: Direct Adjustment of Rates: Incidence of Accidental Injuries among Adolescents in Meadville and Barton

Table 1: Numbers of Unintentional (Accidental) Injuries Among Populations of Adolescents and Young Adults of Meadville and Barton

Meadville	Barton
Age	Population	No. Injuries	Age Specific Rate %	Population	No. Injuries	Age Specific Rate %
15-19	200	14		1,000	20
20-24	1,200	36		100	14
25-29	800	12		400	12
All Ages	2,200	62		1,500	46

Meadville and Barton are two small communities in the Northeast.

1. Calculate the crude cumulative incidence rates of unintentional injuries for Meadville and then for Barton. Show all steps, including numerators and denominators, and the multiplier in the final answer. The final answer should be expressed as a percentage and inserted into Table 1. (4 points)

1. Compare the two crude rates in words. Which is higher, the crude incidence rate of accidental injuries in Barton or in Meadville? (1 point)
2. Calculate the category-specific rates for each of the three age categories in each of the two communities. Again, show all steps and express the final answer as a percentage. Then plug your answers into Table 1. (3 points)
3. Does age appear related to the incidence of accidental injuries in either community? To answer this, look down the columns and see if there is a pattern in the age-specific rates. If there is, please describe it. If not, state this. (2 points)
4. In words, compare the rates between the two communities within each age group. For instance, are they similar among 15-19- year-olds in the two communities? For 20-24-year-olds? For 25-29-year-olds? Here you are looking across, rather than down. (3 points)
5. Using the combined population of the two communities as the standard population, calculate the age-adjusted rates for each community with the direct method. Remember that there is a slide in Lecture 4 which lists all the steps for this. I strongly suggest using it. In addition, Tables 2 and 3 are here to help you. This time you do not need to show all steps in all calculations but fill in both tables. Remember to follow all steps shown in Lecture 4. (8 points)

1. Fill in Table 4. Make sure the final answers are all expressed as percentages. Compare the rates in words. In doing so, address the following:

• Compare again the two crude rates. Which is higher? (1 point)
• Compare the crude rate and age-adjusted rate for Meadville. In which direction did the rate move after age-adjustment? (1 point)
• Compare the crude rate and age-adjusted rate for Barton. In which direction did the rate move after age-adjustment? (1 point)
• Compare the two age-adjusted rates. Now which is higher? Once age is controlled for, what does this tell you about the gap between incidence of accidental injury rates among young adults in the two communities? (2 points)

1. Based only on what you know from these data, what cannot be an explanation for any differences in the age-adjusted rates? (2 points)

Table 2: Direct Age Adjustment for Meadville

Age Group	Number of People in the Standard Population	Age-Specific Incidence Rates for Meadville %	Age-Specific Incidence Rates for Meadville in Decimal Form	Number of Expected Accidental Injuries
15-19
20-24
25-29
Total

Table 3: Direct Age Adjustment for Barton

Age Group	Number of People in the Standard Population	Age-Specific Incidence Rates for Meadville %	Age-Specific Incidence Rates for Meadville in Decimal Form	Number of Expected Accidental Injuries
15-19
20-24
25-29
Total

Table 4: Crude and Age-Adjusted Rates (%)

Community	Crude Incidence Rate for Accidents (Ages 15-29)	Age-Adjusted Incidence Rate for Accidents (Ages 15-29)
Meadville
Barton

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