Development and Validation of a Preoperative Frailty Index Using Health Administrative Data: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Development and Validation of a Preoperative Frailty Index Using Health Administrative Data (NCT03354546), a registered phase not stated study. The primary outcome is Survival for One Year After Surgery.

2. Clinical Question

3. Trial Design

Despite being described in this context as a trial, the official title identifies this as a population-based cohort study. The registry describes creation, evaluation and validation of a preoperative frailty index using health administrative data. The listed intervention is a diagnostic test, the frailty index. The record does not describe random allocation, and its cohort descriptions are not a like-for-like control comparison.

The registered study enrollment is 511285. That is the enrollment figure in the record; it should not be treated as the denominator for the primary analysis because the record does not state how many participants contributed to that analysis. The primary-outcome population description refers to the elective surgery cohort and explicitly says data were not collected from emergency surgery patients. Although an emergency general surgery cohort is described elsewhere in the record, no primary-outcome data for that cohort are reported.

The record lists a start date of 2002-04-01, a primary completion date of 2016-03-31 and a status of completed. Ottawa Hospital Research Institute is listed as sponsor. The brief summary says the index was to be based on the Canadian Study of Health and Aging Frailty Index and standard recommendations for constructing frailty indices. The registry record does not report details of the validation procedures, a protocol, or the allocation of participants between the cohort descriptions.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Analysis population for the primary outcome, as defined in the registry: We measured the unadjusted and adjusted associations between the pFI and postoperative outcomes in our elective surgery cohort. The unadjusted analysis contained only the pFI. Data was not collected from Emergency Surgery patients.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Survival for One Year After Surgery, measured over Date of surgery to 365 days after surgery.

The primary endpoint is survival for one year after surgery. It is defined as still being alive, with no death date in the registered persons database, over the interval from the date of surgery to 365 days after surgery. The registered unit is participants, and the endpoint is binary: each participant is classified according to whether the stated survival condition is met.

In general, a binary endpoint can make a clinical outcome straightforward to describe as an event status over a specified follow-up period. Here, the endpoint gives a fixed postoperative time horizon for assessing survival in relation to the preoperative frailty index. The record describes the exposure as a per 0.1 unit increase in the index, so the intended association concerns a change in the index rather than a treatment assignment.

The registry record does not report the primary endpoint's estimated association with the index, a confidence interval, or a p-value. It also does not report how incomplete follow-up or missing death-date information was handled. Without those results and details, the endpoint definition alone does not show the size, direction or precision of any association.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a population-based cohort study that planned to create, evaluate and validate a preoperative frailty index from health administrative data. It also describes unadjusted and adjusted associations between the pFI and postoperative outcomes in an elective surgery cohort. These descriptions identify the general analysis approach, but they do not provide a full statistical analysis plan or numerical results.

What does an unadjusted association represent?

In general, an unadjusted association describes the relationship between an exposure and an outcome without accounting for other variables in the model. The record says the unadjusted analysis contained only the pFI. It does not report the estimate, its effect-measure scale, a confidence interval, a p-value or the number of participants included. The exposure is described as per 0.1 unit increase in the index, but no estimated change in survival associated with that increase is reported.

What does adjustment add?

In general, an adjusted analysis estimates an exposure-outcome association while accounting for other variables included in the model. Adjustment can address measured differences between people, but its meaning depends on which variables are used, how they are measured and how they enter the model. The record states that adjusted associations were measured, but the adjustment variables and model specification are not reported in the registry record. No adjusted estimate or measure of its uncertainty is posted.

How should the binary endpoint be understood?

The primary endpoint records whether a participant is alive, with no death date in the registered persons database, from surgery to 365 days after surgery. In general, a binary outcome distinguishes whether a defined event status is present over a specified period. The record names survival as the outcome and participants as the unit. It does not report the number classified as alive or the number contributing to the primary analysis. The death counts in the adverse-event information do not substitute for an endpoint estimate or a complete account of primary-outcome data.

What would a confidence interval tell a reader?

In general, a confidence interval expresses the precision of an estimated association by giving a range of values compatible with the data and the statistical method used. A narrow interval indicates greater precision than a wide interval, while an interval spanning values on different sides of the null can leave the direction or statistical compatibility of the association uncertain. No confidence interval is reported for the primary endpoint, so its precision cannot be assessed from the registry record.

What do the planning assumptions mean?

The record describes a sample-size illustration based on an observed effect, rather than the study's own design. Its stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation and an effect to detect defined as a stated fraction of the observed effect. In general, such an illustration asks how many participants per arm might be needed under specified assumptions. It is not observed power, does not show the study's actual allocation, and should not be read as evidence that the observational cohorts were randomized or equal in size. The record does not report that the illustration was the basis for the study design.

The registry states that no analyses are listed. As a result, the methodological descriptions cannot be linked to a posted numerical estimate for the primary endpoint. Details such as model form, covariate selection, missing-data handling and validation performance are not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Elective Surgery")
n      <- c(415704)
events <- c(396164)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Elective Surgery  415704  396164  95.3  95.2  95.4  95.2  95.4  95.2  95.4

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and identifies institutional discharge as a secondary outcome. It lists no analyses. The record does not report how the primary and secondary outcomes were handled together for statistical inference, whether any multiplicity adjustment was planned, or whether any outcomes were selected for emphasis after examining results. These details are not reported in the registry record.

The primary endpoint description defines survival status using the registered persons database and a death-date criterion. It does not explain whether participants with incomplete follow-up, unavailable linkage or missing endpoint information were excluded, classified in another way, or handled through an imputation or sensitivity analysis. Missing-data procedures are not reported in the registry record.

The primary-outcome population is described as the elective surgery cohort, with no data collected from emergency surgery patients. The record does not give the number of participants included in each analysis, the number with complete outcome data, or the reasons for any exclusions. It also does not specify whether the analysis population was defined before examining outcomes. Consequently, the denominator and the relationship between enrollment and the analyzed population cannot be assessed.

The study description mentions both unadjusted and adjusted associations, but the registry record does not report the covariates, model specification, analysis populations or numerical findings for either approach. This limits assessment of the adjustment strategy and of whether different outcome analyses used consistent populations.

12. What the Result Does, and Does Not, Mean

The registry record describes a study intended to develop and validate a preoperative frailty index from health administrative data, and it defines a one-year survival endpoint after surgery. It also describes examining associations between the index and postoperative outcomes in an elective surgery cohort. These details clarify the research question and outcome definition, but the posted results do not report an estimated primary association or its precision.

Accordingly, the record does not establish whether higher or lower pFI values were associated with one-year survival, how large any association was, or how uncertain it was. It also does not provide a result that can establish the index's predictive performance. The endpoint definition and study objective are not substitutes for those estimates.

In general, an observational association is not by itself evidence that an exposure caused an outcome. A frailty index may be evaluated as a predictor, but judging predictive value requires reported performance results and enough information to understand how the index was evaluated. Such estimates and validation details are not reported in the registry record.

The enrollment figure is not an analysis denominator, and the emergency cohort description does not mean emergency patients contributed to the primary outcome: the record specifically says data were not collected from emergency surgery patients. The adverse-event death entries should also not be interpreted as a comparative primary survival result. They do not provide the missing association estimate, uncertainty or analysis population.

13. Why This Trial Matters Statistically

This study addresses a statistical problem that arises when researchers seek to use routinely collected health administrative data to represent a complex construct such as frailty. The registered aim is to create, evaluate and validate a preoperative index based on the Canadian Study of Health and Aging Frailty Index and standard recommendations for creating frailty indices. That aim makes the definition and evaluation of the index central to understanding any association with postoperative outcomes.

Statistically, it is important to distinguish the development of a measure from evidence that it predicts an outcome. The registry describes both index development and associations with postoperative outcomes, but the posted results do not report an association estimate, confidence interval or prediction-performance result. Those missing results prevent assessment of the index's observed relationship with one-year survival or of how precisely any relationship was estimated.

The record also illustrates why population definitions matter. It describes elective and emergency surgical cohorts, but the primary outcome description restricts the analysis population to elective surgery and says emergency surgery data were not collected. Clear cohort-specific denominators and results would be needed to interpret the scope of any findings. Those details are not reported in the registry record.

More broadly, a large enrollment figure does not by itself communicate the precision or applicability of a particular analysis. In general, those depend on the analyzed population, outcome information and analysis method. The registry's enrollment figure is not identified as the primary analysis denominator, and the primary endpoint results are not posted.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting this registry record is that the primary endpoint is defined but its estimated association with the pFI is not reported. No effect estimate, confidence interval, p-value or primary analysis denominator is available in the posted results. The magnitude, direction and precision of the association therefore cannot be evaluated.

The record describes both unadjusted and adjusted analyses but does not identify the adjustment variables or model specifications. It does not report the procedures used to develop and validate the index, the evaluation criteria, or any estimates of predictive performance. These omissions make it difficult to judge how the index was constructed and how its performance was assessed.

The population information is also incomplete for interpreting the primary outcome. Although the registered enrollment is 511285 and two cohort descriptions are listed, the primary-outcome population is the elective surgery cohort, and emergency surgery data were not collected. Cohort-specific enrollment, analysis denominators, exclusions and endpoint completeness are not reported in the registry record.

Missing-data methods, follow-up completeness and the handling of unavailable death-date information are not reported. The record lists two outcome measures and no analyses, but does not describe how multiple outcomes were considered in statistical inference. Finally, because the study is described as a cohort study and no allocation is stated, the listed cohorts should not be treated as randomized intervention and control groups.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Development and Validation of a Preoperative Frailty Index Using Health Administrative Data — NCT03354546.
• Registry record last updated 2024-09-23; status last verified 2024-05.
• Results first posted 2024-09-23.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record for NCT03354546 is titled “Development and Validation of a Preoperative Frailty Index Using Health Administrative Data.” Its official title describes a population-based cohort study. The study aimed to create, evaluate and validate a preoperative frailty index using health administrative data, with the index based on the Canadian Study of Health and Aging Frailty Index and standard recommendations.

Ottawa Hospital Research Institute is listed as sponsor. The record lists enrollment of 511285, a start date of 2002-04-01, a primary completion date of 2016-03-31 and completed status. The primary endpoint is survival from the date of surgery to 365 days after surgery. The primary-outcome population description specifies elective surgery and says emergency surgery data were not collected.

The registry lists institutional discharge as a secondary outcome and lists no analyses. It does not report the primary endpoint estimate, its precision, analysis denominators, adjustment details or missing-data procedures.