Standardization - Health - Lecture Slides, Slides of Public Health

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• **Direct Method
• Indirect Method**

Issue: Often times, we wish to compare

mortality rates between populations, or at

different time periods in one population,

however, the population groups may differ

with respect to underlying characteristics

(e.g. age, gender) that may affect the overall

mortality rate

(hence – not a “fair” comparison).

Standardization accounts for the differing

distributions of the underlying

characteristics

Age Popul. # Deaths % of Popul. Death Rate

Hillsborough 1995 (top) Pinellas 1995 (bottom)

 - 0 to 14 190,703 174 21.4% 0. 

• 15 to 24 115,928 115 13.0% 0.
• 25 to 44 289,441 620 32.4% 0.
• 45 to 64 180,396 1,435 20.2% 0. - 65 + 116,406 5,657 13.0% 0.
• TOTAL 892,874 8,001 100.0% 0. - 0 to 14 138,986 116 15.9% 0. Age Popul. # Deaths % of Popul. Death Rate - 15 to 24 83,815 63 9.6% 0. - 25 to 44 239,396 498 27.3% 0. - 45 to 64 190,427 1,421 21.7% 0. - 65 + 223,576 10,326 25.5% 0.
  • TOTAL 876,200 12,424 100.0% 0.

Direct Standardization:

One way to select the standard population is to

combine population counts from the

populations.

We can then apply the category-specific death

rates to the standard population to calculate

and compare the expected number of deaths in

each population.

Adjusted Death Rate (H) = 21094 / 1,769,074 = 1,192 per 100K Adjusted Death Rate (P) = 20020 / 1,769,074 = 1,132 per 100K

Age-adjusted rate ratio = 1,192 / 1,132 = 1.

Using Hillsborough + Pinellas county as the

standard population:

The age-adjusted 1995 death rate appears to be

approximately 5% higher in Hillsborough county

compared to Pinellas county.

Direct Standardization:

Another way to select the standard population

is to use an external standard population,

such as the United States population.

As before, we can then apply the category-

specific death rates to the standard

population to calculate and compare the

expected number of deaths in each

population.

U.S. Death Rate Expected Deaths Age Popul. H P H P 0 to 14 55,961,000 .0009 .0008 50,364 44,

15 to 24 36,124,000 .0010 .0008 36,124 28,

25 to 44 82,366,000 .0021 .0021 172,968 172,

45 to 64 48,345,000 .0080 .0075 386,760 362,

65 + 32,283,000 .0486 .0462 1,568,953 1,491, Total 255,079,000 ----- ----- 2,215,169 2,100,

Adj. Death Rate (H) = 2,215,169 / 255,079,000 = 868 per 100K

Adj. Death Rate (P) = 2,100,696 / 255,079,000 = 824 per 100K

Adj. Death Rate (H) = 2,215,169 / 255,079,000 = 868 per 100K

Adj. Death Rate (P) = 2,100,696 / 255,079,000 = 824 per 100K

Age-adjusted rate ratio = 868 / 824 = 1.

Using the United States as the standard

population:

The age-adjusted 1995 death rate appears to be

approximately 5% higher in Hillsborough county

compared to Pinellas county.

Axioms (Direct Adjustment):

3. If the stratum-specific rates differ, calculating an

adjusted rate will mask important differences.

Thus, the adjusted rates should be compared

cautiously, and the stratum-specific rates should

be mentioned.

4. The selection of the standard population is

arbitrary. However, when 2 or 3 populations are

being compared, use the sum of the populations.

Axioms (Direct Adjustment):

5. If you believe that one population is not exposed,

and the other may be, choose the non-exposed

group as the standard population.

6. You can choose a “ standard ” standard population:

They usually come in sets of three:

--- Developing World Standard – weighted to the young --- Developed World Standard – weighted to adults --- Global World Standard – average of the above two

Indirect Adjustment:

1. Conceptually similar to direct adjustment, but

uses standard stratum-specific “rates” rather

than standard stratum-specific “weights”

(population counts).

2. Using the standard “rates,” we compare the

the observed number of events to the

expected number of events.

Indirect Adjustment:

THE RESULTS ARE PRESENTED AS THE

“STANDARDIZED MORBIDITY” OR

“MORTALITY” RATIO (SMR)

observed cases (O)

SMR = ------------------------ ( x 100)

expected cases (E)

EXAMPLE: INDIRECT ADJUSTMENT

Underground potash miners vs. general

population

Interpretation: SMR = 105.

We estimate that underground potash

miners have a 6% higher risk of

mortality than the general population.

EXAMPLE: INDIRECT ADJUSTMENT

Underground potash miners vs. general

population

Interpretation: SMR = 105.

But don’t forget about the “healthy worker”

effect (e.g. we expect workers to have a

lower mortality than the general population).

Also, beware that the general population

almost always contains some exposed

individuals (e.g. bias toward the null).