*This figure represents the hypothetical death rate if the study population had the same age structure as the standard population.
function calculateSDR() {
// Get inputs for Group 1
var pop1 = parseFloat(document.getElementById('pop1').value);
var deaths1 = parseFloat(document.getElementById('deaths1').value);
var stdPop1 = parseFloat(document.getElementById('stdPop1').value);
// Get inputs for Group 2
var pop2 = parseFloat(document.getElementById('pop2').value);
var deaths2 = parseFloat(document.getElementById('deaths2').value);
var stdPop2 = parseFloat(document.getElementById('stdPop2').value);
// Get inputs for Group 3
var pop3 = parseFloat(document.getElementById('pop3').value);
var deaths3 = parseFloat(document.getElementById('deaths3').value);
var stdPop3 = parseFloat(document.getElementById('stdPop3').value);
// Get multiplier
var k = parseFloat(document.getElementById('multiplier').value);
// Validation
if (isNaN(pop1) || isNaN(deaths1) || isNaN(stdPop1) ||
isNaN(pop2) || isNaN(deaths2) || isNaN(stdPop2) ||
isNaN(pop3) || isNaN(deaths3) || isNaN(stdPop3)) {
alert("Please fill in all fields with valid numbers.");
return;
}
if (pop1 === 0 || pop2 === 0 || pop3 === 0) {
alert("Study Population cannot be zero.");
return;
}
// 1. Calculate Age-Specific Death Rates (ASDR) for study population (raw fraction)
var asdr1 = deaths1 / pop1;
var asdr2 = deaths2 / pop2;
var asdr3 = deaths3 / pop3;
// 2. Calculate Expected Deaths in Standard Population
var expDeaths1 = asdr1 * stdPop1;
var expDeaths2 = asdr2 * stdPop2;
var expDeaths3 = asdr3 * stdPop3;
// 3. Sum total expected deaths
var totalExpectedDeaths = expDeaths1 + expDeaths2 + expDeaths3;
// 4. Sum total standard population
var totalStdPop = stdPop1 + stdPop2 + stdPop3;
// 5. Calculate Standardized Death Rate
var sdr = (totalExpectedDeaths / totalStdPop) * k;
// Calculate Crude Rate for comparison
var totalStudyDeaths = deaths1 + deaths2 + deaths3;
var totalStudyPop = pop1 + pop2 + pop3;
var crudeRate = (totalStudyDeaths / totalStudyPop) * k;
// Display Results
document.getElementById('result').style.display = 'block';
document.getElementById('crudeRateResult').innerText = crudeRate.toFixed(2) + (k === 1000 ? " per 1,000″ : " per 100,000″);
document.getElementById('sdrResult').innerText = sdr.toFixed(2) + (k === 1000 ? " per 1,000″ : " per 100,000″);
}
How to Calculate Standardized Death Rate (SDR)
The Standardized Death Rate (SDR), also known as the Age-Adjusted Death Rate, is a vital statistical tool used in epidemiology and demography. It allows researchers to compare mortality rates between populations that have different age structures.
Comparing Crude Death Rates directly can be misleading. For example, a developed country with an older population might appear to have a higher death rate than a developing country with a younger population, simply because older people are more likely to die, not because the health conditions are worse.
The Direct Standardization Formula
To calculate the Age-Standardized Death Rate using the direct method, follow these steps:
Calculate Age-Specific Death Rates (ASDR): For each age group in your study population, divide the number of deaths by the population count.
Select a Standard Population: Choose a reference population (e.g., WHO World Standard Population) to provide the weights.
Calculate Expected Deaths: Multiply the ASDR of your study group by the population count of the same age group in the Standard Population.
Sum Expected Deaths: Add up the expected deaths for all age groups.
Divide by Total Standard Population: Divide the sum of expected deaths by the total count of the Standard Population.
Apply Multiplier: Multiply by 1,000 (or 100,000) to express the rate in a readable format.
Mathematically:
SDR = [ Σ ( ASDRi × Standard_Popi ) / Total Standard Population ] × k
Example Calculation
Imagine we want to calculate the SDR per 1,000 people using two age groups (Young and Old) and a Standard Population.
Age Group
Study Pop
Study Deaths
ASDR (Study)
Standard Pop
Expected Deaths
Young
10,000
20
0.002
50,000
100
Old
5,000
100
0.020
20,000
400
Total
15,000
120
—
70,000
500
Total Expected Deaths: 100 + 400 = 500 Total Standard Population: 70,000 Calculation: (500 / 70,000) × 1,000 = 7.14 deaths per 1,000
Why is this important?
Without standardization, you might conclude that a retirement community is less healthy than a college town because the death rate is higher. Standardization removes the effect of age, revealing the true underlying health status of the population relative to a standard benchmark.