function calculateAgeAdjustedRate() {
// Inputs
var mult = parseFloat(document.getElementById('multiplier').value);
var groups = 5;
var totalEvents = 0;
var totalLocalPop = 0;
var totalStdPop = 0;
var groupData = [];
// Gather Data
for (var i = 1; i <= groups; i++) {
var e = parseFloat(document.getElementById('events' + i).value) || 0;
var p = parseFloat(document.getElementById('pop' + i).value) || 0;
var s = parseFloat(document.getElementById('std' + i).value) || 0;
if (p < 0) p = 0;
if (e < 0) e = 0;
if (s < 0) s = 0;
groupData.push({
events: e,
pop: p,
std: s
});
totalEvents += e;
totalLocalPop += p;
totalStdPop += s;
}
if (totalLocalPop === 0 || totalStdPop === 0) {
alert("Please enter valid population numbers greater than zero.");
return;
}
// Calculate Crude Rate
// Crude Rate = (Total Events / Total Population) * Multiplier
var crudeRate = (totalEvents / totalLocalPop) * mult;
// Calculate Age-Adjusted Rate
// Formula: Sum of ( (Group Events / Group Pop) * (Group Std Pop / Total Std Pop) ) * Multiplier
var weightedSum = 0;
for (var i = 0; i 0) {
asr = row.events / row.pop;
}
// Weight (Standard Pop Proportion)
var weight = row.std / totalStdPop;
// Add weighted contribution
weightedSum += (asr * weight);
}
var ageAdjustedRate = weightedSum * mult;
// Display Results
document.getElementById('results').style.display = 'block';
document.getElementById('crudeRateResult').innerHTML = crudeRate.toFixed(2);
document.getElementById('adjRateResult').innerHTML = ageAdjustedRate.toFixed(2);
document.getElementById('totalEventsResult').innerHTML = totalEvents.toLocaleString();
document.getElementById('totalPopResult').innerHTML = totalLocalPop.toLocaleString();
}
Understanding Age-Adjusted Rates
The Age-Adjusted Rate is a statistical technique used to compare rates (such as mortality or disease incidence) between populations that have different age structures.
Without adjustment, a population with a higher proportion of older adults will naturally have a higher crude death rate, even if the health conditions of the two populations are identical.
Why Crude Rate isn't enough
The Crude Rate is simply the total number of events divided by the total population. While accurate for the specific population, it can be misleading when comparing different groups.
For example, State A (retirement hub) might have a higher crude death rate than State B (college town) simply because its residents are older, not because it is less healthy.
How the Calculation Works
This calculator uses the Direct Method of standardization:
Age-Specific Rates: The rate is calculated separately for each age group (e.g., Deaths in 0-19 / Population in 0-19).
Standard Population Weights: A "standard" population (often the U.S. 2000 Standard Population or a WHO standard) determines the weight of each age group.
Weighted Average: The age-specific rates are multiplied by the standard weights and summed together to produce the final adjusted rate.
Interpreting the Results
If Adjusted Rate < Crude Rate: Your population is likely older than the standard population. The raw numbers look worse because of the age factor.
If Adjusted Rate > Crude Rate: Your population is likely younger than the standard population. The raw numbers look better than they actually are relative to the standard.
Standard Population Reference
The default values in the "Standard Population" column are approximations based on general demographic standards (summing to 1,000,000).
Researchers often use specific distributions like the U.S. 2000 Standard Population for official reporting. You can edit the "Standard Population" column in the calculator above to match whichever standard reference you are required to use.