How do you calculate the frailty index score?

Oct 24, 2025 3 min read •

Geriatrics public health Clinical Assessment

According to a study published in Age and Ageing, a robust frailty index can condense many health variables into a single score that accurately quantifies an individual's overall health. So, how do you calculate the frailty index score? The process is based on the deficit accumulation model, where the score is derived by dividing the total number of health deficits an individual has by the total number of deficits considered.

Quick Summary

The frailty index is calculated as the ratio of an individual's accumulated health deficits to the total number of deficits assessed. This score provides a continuous measure of health, with higher values indicating a greater degree of frailty. The method is adaptable, allowing for different data sources and items to be included in the calculation.

Key Points

Core Calculation: The frailty index is a ratio: total accumulated health deficits divided by the total number of deficits assessed.
Variable Scoring: Each health deficit item is recoded to a numerical value, typically from 0 (no deficit) to 1 (full deficit), to enable calculation.
Data Inclusion: A reliable frailty index requires at least 30-40 variables covering multiple health domains, such as symptoms, diseases, and functional abilities.
Clinical Categories: Frailty index scores are often grouped into categories like robust, pre-frail, and frail to facilitate clinical interpretation and care planning.
Data Handling: When calculating the score, individuals with excessive missing data (typically >20% of items) may be excluded, but the denominator is adjusted for those with valid scores.
Automation: Electronic frailty indices (eFIs) automatically calculate scores using data from electronic health records, enhancing efficiency in clinical settings.
Higher Score, Higher Frailty: A score closer to 1 indicates a greater degree of frailty and a higher risk of adverse health outcomes.

The frailty index (FI) is a widely used and flexible tool for assessing an individual's health status based on the accumulation of health deficits. It can utilize various data sources, including surveys and electronic health records. This approach is rooted in the deficit accumulation model, which posits that health deficits increase with age, leading to greater vulnerability. Deficits are countable health issues like diseases, symptoms, or disabilities. A valid FI typically includes 30 to 40 variables across multiple body systems to ensure a reliable measure.

Step-by-Step Guide to Calculating the Frailty Index Score

Based on a procedure outlined by researchers, here's a summary of the key steps for calculating a frailty index from existing data:

Select Deficit Variables: Choose variables from the dataset that represent health problems or deficits, such as illnesses or functional limitations.
Filter for Missing Data: Exclude variables with more than 5% missing information. For individuals, the denominator is adjusted if a few items are missing.
Recode Responses: Convert each variable's response into a score between 0 (no deficit) and 1 (full deficit). This involves assigning graded scores for non-dichotomous variables.
Refine Variable List: Remove variables that are either too rare (under 1%) or too common (over 80%) to ensure they contribute meaningfully to the score.
Calculate the Score: Sum the recoded deficit scores for an individual and divide by the total number of valid deficit variables used.
- Formula: FI = (Sum of Deficit Scores) / (Total Number of Non-Missing Items)
Analyze the Index: Evaluate the distribution and association with age. Valid FIs usually show a right-skewed distribution and increase with age, with scores generally not exceeding 0.7.

Understanding the Frailty Score and its Categories

The frailty index provides a continuous score ranging from 0 to 1, where higher scores indicate more accumulated deficits and greater frailty. While continuous, scores are often categorized for easier clinical interpretation:

Robust: FI < 0.12
Mild Frailty: FI 0.12–0.24
Moderate Frailty: FI 0.25–0.36
Severe Frailty: FI > 0.36

It's important to remember that these categories and cutoffs can vary based on the context and the specific index used.

Comparison: Frailty Index vs. Other Frailty Assessment Tools

The Frailty Index differs from other methods like the Fried Phenotype. The table below outlines key differences:


Feature	Frailty Index (Deficit Accumulation)	Fried Frailty Phenotype
Method	Calculated ratio of deficits to total items.	Assessed using five specific physical criteria.
Deficit Criteria	Flexible set of 30-70+ deficits.	Fixed at five criteria.
Output	Continuous score (0 to 1).	Categorical score (robust, pre-frail, frail).
Data Source	Adaptable to various sources.	Requires specific performance measures.
Key Advantage	High sensitivity and predictive power.	Straightforward for screening.
Key Limitation	More complex calculation, requires robust data.	Less sensitive to subtle changes, requires specific equipment.

Using an Electronic Frailty Index (eFI)

Electronic frailty indices (eFIs) utilize data from electronic health records (EHRs) to automate frailty calculation. They extract data from coded information like diagnoses and lab results, providing efficient assessment, particularly in primary care. An example is the 36-deficit eFI used in England.

Conclusion

Calculating the frailty index involves a systematic process based on the deficit accumulation model. By quantifying accumulated health deficits from available data, the FI provides a continuous score reflecting an individual's health status and vulnerability. This method is flexible, comprehensive, and has strong predictive value, making it valuable for research and clinical tools like the electronic frailty index.

Outbound Link: For a detailed, scholarly look at the procedure for creating a frailty index, consult the guide published by Olga Theou and colleagues.

Frequently Asked Questions

The frailty index is based on the deficit accumulation model, which measures an individual's overall health by counting the number of health deficits they have. The score is a proportion, indicating how many problems exist relative to the total number of health variables being assessed.

Deficits are scored numerically, typically on a scale from 0 to 1. For simple yes/no responses, they are coded as 1 for a deficit and 0 for no deficit. For questions with multiple answers, a graded scale is used (e.g., 0, 0.5, 1), and continuous variables can be recoded using cut-points.

There is no single 'normal' score, as frailty increases with age. However, in community-dwelling populations, most individuals have low scores, and scores over 0.7 are rare. For example, some clinical interpretations classify a score of less than 0.12 as 'fit' or 'robust'.

Yes, a frailty index can be constructed from existing health data, including patient surveys or personal health records, as long as a minimum number of deficits (typically 30 or more) are assessed. The same methodology of counting and dividing deficits can be applied.

A frailty index requires data on various health deficits, which can be collected via survey, comprehensive geriatric assessment, or from administrative and electronic medical records. The items can include symptoms, diseases, disabilities, and abnormal lab values.

Individuals with a small percentage of missing deficit items (typically under 20%) can still have a frailty index calculated by simply adjusting the denominator to reflect the number of items that were successfully measured. Variables with too many missing values may be excluded entirely.

The primary difference is the assessment model. The frailty index uses a deficit accumulation model based on a flexible, comprehensive list of health deficits, resulting in a continuous score. The Fried phenotype uses a fixed set of five physical performance criteria, resulting in a categorical classification (robust, pre-frail, or frail).

An eFI is a version of the frailty index that uses data automatically extracted from electronic health records (EHRs). It is designed to help clinicians in primary care settings identify and monitor patients who may be at risk for frailty without manual calculation.

References

Medical Disclaimer

This content is for informational purposes only and should not replace professional medical advice. Always consult a qualified healthcare provider regarding personal health decisions.