4Rates and Standardization

Chapter4 p67

Rates To make comparisons among groups more meaningful, rates may be used instead of raw numbers.Rate = the number of cases of a particular outcome of interest that occur over a given period of time / the size of the population in that time periodInfant mortality rate = number of deaths during a calendar year among infants under one year of age / the total number of live births during that year (unit = per 1000 live births)

Chapter4 p70

Figure 4.1 Trends in the crude marriage and divorce rates, USA, 1950-1994.

Employment status Population Impairments Rates per 1000

Currently employed 98917 552 5.58

Currently unemployed 7462 27 3.62

Not in the labor force 56778 368 6.48

Total 163157 947 5.80

Currently employed Not in the labor force

Age Population % Population %

17 – 44 67987 68.7 20760 36.6

45 – 64 27592 27.9 15108 26.6

65+ 3338 3.4 20910 36.8

Total 98917 100 56778 100

Standardization of rates

It appears that individuals who are not in the labor are at greater risk of hearing impairment due to injury than those who are currently employed.

Age groupDiffer in age composition individuals not included in the labor force are older than those who are currently employed

Hearing impairment due to injury reported by individuals 17 years of age and older in 1980-1981

= 947/163157

Age Population Impairments Rates per 1000

17 – 44 94930 441 4.65

45 – 64 43857 308 7.02

65+ 24370 198 8.12

Total 163157 947 5.80

Age-specific impairment rates in the surveyed population as a whole

Age-specific impairment rates for the two subpopulations, Currently employed and Not in the labor force

Currently employed Not in the labor force

Age Population impairments Rate per 1000

Population impairments Rate per 1000

17 – 44 67987 346 5.09 20760 80 3.85

45 – 64 27592 179 6.49 15108 117 7.74

65+ 3338 27 8.09 20910 171 8.18

Total 98917 552 5.58 56778 368 6.48

How many impairments in the age group 17-44, 45-64, and 65+ for the currently unemployment subpopulation?

15, 12, 0

= 441/94930

= 80/20760

Expected age-specific impairment rates for the two subpopulations, using Currently employed rate per 1000 and Not in the labor force rate per 1000

Total Currently employed Not in the labor force

Age (1) Population (2)

Rate per 1000

(3) Expected impairments

(4)

Rate per 1000

(5) Expected impairments

17 – 44 94930 5.09 483.2 3.85 365.5

45 – 64 43857 6.49 284.6 7.74 339.5

65+ 24370 8.09 197.2 8.18 199.3

Total 163157 965.0 6.48 904.3

(3) = (1) x (2)/1000 (5) = (1) x (4)/1000

Age-adjusted impairment rates for the Currently employed and Not in the labor forceCurrently employed : 965.0/163157 = 5.91 per 1000Not in the labor force : 904.3/163157 = 5.54 per 1000

After we control for the effect of age, impairment rates for the currently employed > impairment rate not in the labor forceopposite of what we observed when we looked at the crude rates influenced by the age structure

Direct method of standardization

Expected age-specific impairment rates for the two subpopulations, using Currently employed rate per 1000 and Not in the labor force rate per 1000

Total Currently employed Not in the labor force

Age (1) Rate per 1000 (2) Population (3) Expected impairments

(4) Population (5) Expected impairments

17 – 44 4.65 67987 316.1 20760 96.5

45 – 64 7.02 27592 193.7 15108 106.1

65+ 8.12 3338 27.1 20910 169.8

Total 98917 536.9 56778 372.4

(3) = (1) x (2)/1000 (5) = (1) x (4)/1000

Currently employed : 552/536.9 = 1.03Not in the labor force : 368/372.4 = 0.99

The currently employed individual has a 3% higher impairment rate than the surveyed populationThose not in the labor force individual has a 1% lower

Direct method of standardization is used more often than the indirect method.

Indirect method of standardization

surveyed population rate

Chapter4 p77

HIV – a new disease

Vertical bars = change in disease classification

The standardized rates were calculated by means of the direct method the US population in 1940

The adjusted rates have been decreasing for the most part except the HIV death rate.

Chapter4 p82

Figure 4.3 Death rates from leading causes of death for men and women 25 to 44 years of age, USA, 1982-1992

Subgroup death rates for men and women

Chapter4 p83

such as calendar years, age

Direct method of standardization subgroup-specific rates should have the same general trends in all groups being compared, as shown in Fig. 4.4(a)

Chapter4 p83

such as calendar years, age

A somewhat less ideal situation occurs when the trends are not parallel

Chapter4 p83

such as calendar years, age

The subgroup-specific rates follow very different patterns in the two populations, Direct method of standardization should not be attempted.

Chapter4 p84

The graph most closely resembles Fig. 4.4(b) direct method of standardization is appropriate to use

Chapter4 p87

Applications

Chapter4 p66

Exercise