.calc-container {
max-width: 600px;
margin: 20px auto;
padding: 25px;
background-color: #f9f9f9;
border: 1px solid #e1e1e1;
border-radius: 8px;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-title {
text-align: center;
color: #2c3e50;
margin-bottom: 20px;
font-size: 24px;
font-weight: 700;
}
.calc-input-group {
margin-bottom: 15px;
}
.calc-label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #34495e;
}
.calc-input {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box; /* Ensures padding doesn't affect width */
}
.calc-btn {
width: 100%;
padding: 12px;
background-color: #3498db;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
font-weight: 600;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #2980b9;
}
.calc-results {
margin-top: 25px;
background-color: #fff;
padding: 20px;
border: 1px solid #ddd;
border-radius: 4px;
display: none;
}
.calc-result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #eee;
}
.calc-result-row:last-child {
border-bottom: none;
}
.calc-result-label {
color: #7f8c8d;
}
.calc-result-value {
font-weight: 700;
color: #2c3e50;
font-size: 18px;
}
.calc-error {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
font-weight: bold;
}
.article-content {
max-width: 800px;
margin: 40px auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
}
.article-content h2 {
color: #2c3e50;
border-bottom: 2px solid #3498db;
padding-bottom: 10px;
margin-top: 40px;
}
.article-content h3 {
color: #34495e;
margin-top: 25px;
}
.article-content p {
margin-bottom: 15px;
}
.article-content ul {
margin-bottom: 15px;
padding-left: 20px;
}
.article-content li {
margin-bottom: 8px;
}
.formula-box {
background-color: #f1f8ff;
padding: 15px;
border-left: 4px solid #3498db;
font-family: monospace;
margin: 20px 0;
font-size: 1.1em;
}
function calculateAttrition() {
var initialInput = document.getElementById('initialN');
var finalInput = document.getElementById('finalN');
var errorDiv = document.getElementById('errorMessage');
var resultsDiv = document.getElementById('resultsArea');
// Parse inputs
var initialN = parseFloat(initialInput.value);
var finalN = parseFloat(finalInput.value);
// Reset display
errorDiv.style.display = 'none';
resultsDiv.style.display = 'none';
errorDiv.innerHTML = ";
// Validation Logic
if (isNaN(initialN) || isNaN(finalN)) {
errorDiv.innerHTML = 'Please enter valid numbers for both fields.';
errorDiv.style.display = 'block';
return;
}
if (initialN <= 0) {
errorDiv.innerHTML = 'Initial sample size must be greater than 0.';
errorDiv.style.display = 'block';
return;
}
if (finalN initialN) {
errorDiv.innerHTML = 'Final participants cannot exceed initial sample size.';
errorDiv.style.display = 'block';
return;
}
// Calculation Logic
var dropouts = initialN – finalN;
var attritionRate = (dropouts / initialN) * 100;
var retentionRate = (finalN / initialN) * 100;
// Display Logic
document.getElementById('attritionRateResult').innerHTML = attritionRate.toFixed(2) + '%';
document.getElementById('retentionRateResult').innerHTML = retentionRate.toFixed(2) + '%';
document.getElementById('dropoutsResult').innerHTML = dropouts;
resultsDiv.style.display = 'block';
}
Understanding Attrition Rate in Research Studies
In the context of clinical trials, longitudinal studies, and survey research, attrition refers to the loss of participants over the course of a study. It is also frequently referred to as "experimental mortality" or "dropout rate." Understanding how to calculate attrition rate in a research study is critical for maintaining internal validity and statistical power.
High attrition rates can introduce bias, known as attrition bias, particularly if the participants who leave the study share specific characteristics (e.g., participants with severe side effects dropping out of a drug trial). This skews the results, making the remaining pool of participants unrepresentative of the original sample.
The Attrition Rate Formula
The calculation for attrition is straightforward. It compares the number of participants who dropped out to the number of participants present at the start of the study.
Attrition Rate (%) = (Number of Dropouts / Initial Sample Size) × 100
Conversely, the Retention Rate measures the percentage of participants who remained until the end of the study:
Retention Rate (%) = (Final Sample Size / Initial Sample Size) × 100
Example Calculation
Imagine a longitudinal psychology study focusing on sleep patterns. The research begins with an initial cohort.
- Initial Sample Size: 500 participants
- Final Sample Size (Completers): 425 participants
First, we calculate the number of dropouts:
500 – 425 = 75 dropouts
Next, we apply the formula:
(75 / 500) × 100 = 15%
The study has a 15% attrition rate and an 85% retention rate.
Why Attrition Matters in Statistics
When calculating sample size requirements (Power Analysis) before a study begins, researchers must anticipate the attrition rate. If a statistical test requires 100 participants to detect a significant effect, enrolling exactly 100 participants is risky. If the expected attrition rate is 20%, the researcher must over-recruit to ensure the final sample size remains above the required threshold.
Factors Influencing Attrition
- Study Duration: Longer studies naturally tend to have higher dropout rates.
- Invasiveness: Studies requiring painful procedures or sensitive questions often see higher attrition.
- Incentives: Lack of compensation or reimbursement for time can reduce retention.
- Logistics: Frequent travel requirements or complex scheduling can discourage participation.
Acceptable Attrition Rates
While there is no universal "safe" number, many academic journals view attrition rates below 5% as negligible and rates above 20% as problematic. However, this varies by field. In internet-based surveys, attrition can be significantly higher, whereas in life-saving clinical trials, it may be lower.
Use the calculator above to quickly determine the dropout percentage for your study and report it accurately in your methodology section.