standardization prof iain crombie. crude mortality rate total no. of deaths total population for...
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Standardization
Prof Iain Crombie
Crude mortality rate
Total no. of deathsTotal population for specific time period
60,281 deaths * 1,0005,120,000 population
in Scotland in 1999
Crude mortality rate 11.8 per 1,000
Crude mortality rates 1999
0
2
4
6
8
10
12
14
Scotland Kazakhstan Costa Rica
Crude mortality rates • Crude mortality rate depends on the age / sex
structure of the population
• A country with a higher proportion of old people will have a higher number of deaths and a higher crude mortality rate
0-14 years:Scotland: 15%Kazakhstan: 28%Costa Rica: 34%
65+ years:Scotland: 13%Kazakhstan: 7%Costa Rica: 5%
Mortality in New Zealand
Maori 490Non-Maoris 762
All cause mortality per 100,000
Age specific mortality rates
Comparing pyramids
Crude mortality heavily influenced by age distribution
Solution: direct standardisation
Take the age specific rates from population of interest Apply them to a standard populationCalculate the new death rate
if the age specific rateshad occurred in the standard population
Obtain an age standardised ratewhich adjusts for the effect of age
The new world standard population
A simplified calculation: Maori mortality rates
Standard population
(1)
Age specific death rates per 100,000
(2)
Expected deaths
(3)= (1) x (2) / 100000
0-4 8860 258 22.86
5-14 17290 30 5.19
15- 24 16690 120 20.03
25-44 29280 221 64.71
45 – 64 19680 1324 260.56
65 + 8200 6424 529.02
100,000 902.37
eg 0-4 yrs: 8860 x (258/100,000) = 22.86eg 65+ yrs: 8200 x 0.06424 = 529.2
Age standardised rate = 902.37 per 100,000
Alternative calculation: if death rates loweg epilepsy
Standard population
(1)
Age specific death rates per 100,000
(2)
Expected deaths
(3)= (1) x (2)*
0-4 8860 0.0 0
5-14 17290 0.7 12,103
15- 24 16690 0.9 15,021
25-44 29280 2.5 73,200
45 – 64 19680 3.8 74,784
65 + 8200 3.1 25,420
100,000 203,528
•do not divide by100,000 until the end•Age standardised rate = 203528 ÷ 100,000 = 2.04
Summary of direct standardisation
select standard population no. of people in each age groupobtain age specific death rates
Comparing
Crude Age standardisedMaori 490 902Non-Maori 762 502
Why does age adjustment increase Maori rates and decrease Non-Maori rates?
Types of standard population
world European national
US Australia
All Cancers Excluding Non-Melanoma Skin Cancer Countries of the UK, 2009
England Wales Scotland N. Ireland
Crude rate Men 528 623 567 485
Women 495 562 571 462
Age standardised
Men 424 450 452 451
Women 367 386 407 387
Indirect standardisation:studying sub-groups
• Among doctors 14 cirrhosis deaths observed in 1970– 14/43570 = 32 per 100,000 per year
• How does this compare to the UK average
• Too few to calculate reliable age specific rates• Need another method
– indirect standardisation– calculate Standardised Mortality Ratio – SMR– apply national age specific rates to the total group of doctors
SMR = O / E * 100
The basis of the SMR calculation
Calculate the expected deaths if the national age specific rates had occurred in the local population
Compare observed (O)with expected deaths (E)
Indirect standardisation: Farmers and mortality
Death rate per 100,000
(1)
No. of farmers
(2)
Expected deaths
(1) x (2) / 100000
20-24 138.3 7980 11
25-34 159.4 37,030 59
35-44 286.8 60,838 174
45–54 821.2 68,687 564
55-64 2295.3 55,565 1275
2083
Standardized Mortality Ratio
Observed deaths = 1464Expected deaths = 2083 O/E = 1464/2083 = 0.703 Standardized Mortality Ratio (O / E x 100) = 70.3
SMR = 70.3
Indirect standardisation:doctors and cirrhosis, 1921
E&W cirrhosis mortality
Per 1,000,000
No. of doctors
(2)
Expected deaths
(1) x (2) / 1,000,00015-24 5.859 1080 0.00632825-34 13.050 12860 0.16782335-44 46.937 11510 0.54024545-54 161.503 10330 1.66832655-64 271.358 7790 2.113879
4.4966004
If observed deaths = 14
O / E = 14 / 4.497 = 3.11
SMR = 311 %
SMRs for alcohol-related mortality, 2001
Occupation SMR
Bar staff 401
Window cleaners 235
Chefs, cooks 226
Hairdressers 200
Painters and decorators 171
Heavy goods vehicle drivers 67
Van drivers 54
Doctors 27
Clergy 25
IT managers 22
SMR for Cirrhosis mortality by Social Class
Year I II IIIN IIIM IV V1991 67 75 115 97 119 142
1921 158 183 66 69 86
What do the data show?
What you should know about standardizationadjusts for differences in population structure
commonly adjust for age distribution separately by gender can adjust for other factors
types of populations that may differ in age structuredeveloping and developed countriesone country at two time periodsoccupational groups social class
two methodsdirect – age standardized rate indirect – SMR
• small populations – eg regions, occupational groups
