This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Epidemiology of Acute Kidney Injury in England - 1998 to 2013 (NCT02216695), a registered phase not stated study. The primary outcome is Secular Trends in the Mortality After Acute Kidney Injury From 1998 to 2013.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02216695 |
| Phase | Phase not stated |
| Condition | Acute Kidney Injury |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 64882 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University Hospitals of Derby and Burton NHS Foundation Trust |
| Results posted | Yes |
2. Clinical Question
Population
People in England with acute kidney injury (AKI), described as a retrospective cohort. The registry record lists enrollment of 64882, but does not explain how this enrollment relates to the patients included in each analysis or provide further eligibility details.
Intervention
There is no assigned intervention described. The study examines the epidemiology of AKI using national hospital-discharge and census data, rather than testing a treatment or prevention strategy.
Comparator
No randomized or like-for-like control group is described. The planned questions concern trends across calendar periods, age groups, and AKI categories, but the registry record does not specify the exact comparison groups used in each analysis.
Primary question
How did mortality after AKI change in England from 1998 to 2013? The primary outcome is described as secular trends in mortality after AKI, with follow-up during the hospital stay. The registry record does not report the resulting mortality estimates or the direction and size of any trend.
The study’s stated motivation is that the population incidence of AKI in England was not known. Its stated aim is broader than the primary mortality outcome: to examine incidence of AKI not requiring dialysis and AKI requiring dialysis, associated mortality, and determinants across the period. These aims are epidemiological. They concern the occurrence and distribution of AKI and outcomes among people with AKI, not the causal effect of an assigned treatment.
The listed secondary outcomes focus on mortality by age group and by five-year period. The registry record does not report the definitions used to identify AKI, the data linkage procedures, or the covariates considered as possible determinants. Those details would be important for judging how the clinical question was translated into measurable comparisons.
3. Trial Design
This is described as a retrospective cohort study of patients with AKI in England. The study concerns national trends over 1998 to 2013 and is marked completed in the registry record. Its stated purpose is to combine the national database of hospital discharges with national census data. The record describes no assigned treatment, random allocation, or prospective intervention.
The listed enrollment is 64882. The registry record does not explain whether this number represents people, hospital records, a particular analysis population, or all records used across the different analyses. It also does not give selection criteria, the AKI identification algorithm, or details about how repeated admissions or records were handled. The enrollment figure should therefore not be treated as a reported count for each specific outcome analysis.
The primary outcome is secular trends in mortality after AKI from 1998 to 2013. The stated follow-up is the duration of the hospital stay, described as an average of 15 days. The secondary outcomes concern mortality within age groups and across five-year periods. The overall study purpose also refers to trends in incidence for AKI requiring dialysis and AKI not requiring dialysis, and to determinants of AKI-related outcomes. The registry record lists four outcome measures and five analyses but does not map each analysis to a specific model or comparison.
Because this is an observational cohort, comparisons across periods or groups may reflect differences in patient mix, clinical practice, coding, or data collection as well as changes in the underlying epidemiology. The design can describe patterns in the records analyzed, but it does not by itself establish that a particular factor caused a change in mortality. The registry record does not report a protocol, a detailed statistical analysis plan, or the methods used to address such differences.
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
| Stage | Acute Kidney Injury |
|---|---|
| STARTED | 64882 |
| COMPLETED | 64882 |
| NOT COMPLETED | 0 |
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.
| Characteristic | Unit | Acute Kidney Injury |
|---|---|---|
| Participants analysed | 64882 | |
| Age, Continuous | years | 59.7 (58.4 to 61) |
| Gender: Female | Participants | 24859 |
| Gender: Male | Participants | 40023 |
| Region of Enrollment: United Kingdom | participants | 64882 |
| AKI identified by ICD10 codes of N17 | participants | 64882 |
6. Primary Endpoint
The registry lists the primary outcome as Secular Trends in the Mortality After Acute Kidney Injury From 1998 to 2013, measured over Participants will be followed for the duration of hospital stay (average of 15 days).
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is described as mortality after acute kidney injury, assessed during the hospital stay. The record characterizes the outcome as a count of participants with an event and gives the unit as participants. In this context, the event is death during the relevant hospital follow-up; however, the registry record does not provide a more detailed operational definition, such as the source or coding used to classify deaths.
Mortality is used because it is a clinically important outcome and because the study aims to describe how outcomes after AKI varied over time. A trend analysis can show whether the recorded burden of death among the cohort changed across calendar periods. It can also motivate questions about changes in patient characteristics, recognition of AKI, care, or data capture. Descriptive trends alone cannot establish which explanation accounts for any observed pattern.
The stated follow-up is the duration of the hospital stay, with an average of 15 days. This defines a hospital-based observation window rather than a stated long-term follow-up period. Deaths occurring after discharge are not described as part of the primary endpoint. The registry record does not report the number of deaths, the mortality estimate, a confidence interval, or a statistical test for the primary outcome. It also does not give a precise denominator for each mortality analysis, so no risk or rate should be inferred from the endpoint description alone.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the question and design but does not report the primary mortality result. It gives no estimate of mortality after AKI, no comparison across calendar periods, and no uncertainty interval or test result. Consequently, the record alone does not establish whether mortality rose, fell, or remained stable from 1998 to 2013, nor how precise any such trend might be.
The same distinction applies to the broader epidemiological aims. The study description says it was intended to investigate incidence of AKI requiring dialysis and AKI not requiring dialysis, associated mortality, and determinants. The record does not provide incidence estimates, subgroup results, determinant estimates, or corresponding measures of uncertainty. The secondary outcome titles identify mortality by age group and by five-year period, but do not report the results for those groups or periods.
For a trend estimate to be interpretable, the underlying outcome definition and the population represented at each time point matter. Changes in diagnostic coding, hospital discharge practices, data completeness, or the mix of people admitted could affect the pattern in administrative records. The registry record does not state how these issues were assessed. It also does not specify whether reported trends, if any, were adjusted for differences among patients or hospitals.
Confidence intervals, when reported, describe the statistical uncertainty around an estimate under the assumptions of the analysis. They do not account automatically for systematic errors such as misclassification or incomplete capture. No confidence interval is reported for the primary endpoint in this record, so the precision of the mortality estimate cannot be evaluated from it.
The enrollment figure of 64882 is not a substitute for the number of people contributing to each endpoint analysis. The record does not explain the analysis denominators, and the enrollment should not be used to infer event counts or mortality rates. The duration of hospital follow-up is described as an average of 15 days, but no distribution of follow-up or outcome ascertainment after discharge is reported.
Accordingly, the supported interpretation is limited to the study’s stated purpose, cohort design, outcome definitions at a broad level, and analysis topics. Any numerical claims about the magnitude, direction, or statistical significance of mortality trends would require results that are not reported in the registry record.
9. Statistical Methods Explained
The registry description identifies an observational, retrospective cohort approach. In general, a cohort analysis follows or reconstructs a defined group and measures outcomes within that group. A retrospective design uses information already collected, rather than assigning an intervention and prospectively observing its effects. Here, the stated data sources are the national database of hospital discharges and national census data. The registry record does not describe the linkage, data cleaning, or analytic procedures used with those sources.
What does a binary outcome mean?
In general, a binary outcome classifies each eligible observation according to whether an event occurred. The primary outcome is mortality after AKI, and the record characterizes the outcome as participants with an event, expressed as a count. A count alone does not communicate the chance of death unless the relevant denominator and observation period are also clear. The registry record does not report the event count or the denominators used in the primary analysis.
What is a secular trend?
In general, a secular trend is a pattern over calendar time, rather than a comparison created by randomized assignment. The primary outcome title specifies a trend in mortality from 1998 to 2013. To interpret such a trend, readers need to know how calendar time was represented, whether the analysis modeled time continuously or compared periods, and whether other differences were adjusted for. Those methods are not reported in the registry record. The secondary outcome titles indicate analyses by age group and by five-year period, but the record does not provide the group definitions or model specifications.
How should uncertainty be read?
In general, a confidence interval gives a range of values compatible with the data and the statistical model at a stated confidence level. Its width reflects statistical precision, while its interpretation depends on the model and the quality of the underlying measurements. A narrow interval does not correct for biased case identification, missing records, or an inappropriate comparison. No confidence intervals or primary outcome estimates are reported in the registry record, so there is no basis for assessing precision or statistical compatibility of the trend with particular values.
Why do denominators and data definitions matter?
For an event count to be interpretable as a risk or rate, the analysis must define who was eligible to experience the event and how long they were observed. This is especially relevant when follow-up is based on hospital stay. The record states that participants will be followed for the duration of hospital stay, with an average of 15 days, but does not report how stays were counted, whether people could contribute multiple admissions, or how deaths were ascertained. The average follow-up description does not establish that every participant had the same observation time.
The stated use of discharge data and census data suggests an aim to examine population-level patterns, but the registry record does not explain how the two sources were combined or how population denominators were defined. It also does not report how AKI requiring dialysis was distinguished from AKI not requiring dialysis. These definitions affect which cases are included and how trends can be compared over time.
What can planning calculations tell readers?
In general, sample-size calculations estimate the number of participants needed under specified assumptions to detect a chosen effect with a chosen statistical power. They are planning illustrations, not evidence that a study had that power after data collection. The registry record describes planning assumptions based on an observed effect, equal allocation, a two-sided significance level of 0.05, and a normal approximation. It also distinguishes event totals for time-to-event calculations from participants per arm for other calculations. Those assumptions do not establish that this retrospective cohort used equal allocation or that those calculations governed its design. The record does not report the study’s own sample-size justification. Since no recalculated estimates or underlying effect values are included in the record, no numerical planning result can be interpreted from it.
Statistical methods such as regression can, in general, account for measured differences among groups, while methods for time-to-event outcomes can account for different observation times. The registry record does not state that either approach was used. It does not identify a model, covariates, standard-error method, adjustment strategy, or diagnostic procedure. These methods therefore cannot be attributed to the study on the basis of the registry description.
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.
| Arm | Participants | Events | Observed % | Clopper-Pearson 95% CI | Wilson 95% CI | Bayesian 95% credible interval |
|---|---|---|---|---|---|---|
| 1998-03 | 4268 | 1296 | 30.4% | 29.0% to 31.8% | 29.0% to 31.8% | 29.0% to 31.8% |
| 2003-08 | 12434 | 3763 | 30.3% | 29.5% to 31.1% | 29.5% to 31.1% | 29.5% to 31.1% |
| 2008-13 | 48180 | 19793 | 41.1% | 40.6% to 41.5% | 40.6% to 41.5% | 40.6% to 41.5% |
R code and output
arm <- c("1998-03", "2003-08", "2008-13")
n <- c(4268, 12434, 48180)
events <- c(1296, 3763, 19793)
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 1998-03 4268 1296 30.4 29.0 31.8 29.0 31.8 29.0 31.8
ARM 2003-08 12434 3763 30.3 29.5 31.1 29.5 31.1 29.5 31.1
ARM 2008-13 48180 19793 41.1 40.6 41.5 40.6 41.5 40.6 41.511. Multiplicity, Missing Data and Analysis Populations
The registry record lists four outcome measures and five analyses. It identifies mortality after AKI as the primary outcome and names secondary mortality analyses by age group and by five-year period. The record does not describe how the remaining outcome measures or analyses relate to these objectives, or which comparisons were designated as confirmatory rather than exploratory.
When an analysis makes several statistical comparisons, the chance of at least one apparently notable result can increase. In general, multiplicity procedures can control that concern, but they may also affect the precision or interpretation of individual estimates. The registry record does not report whether any adjustment for multiple outcomes, subgroups, periods, or analyses was planned or applied. It also does not state whether the analyses were prespecified in a protocol.
Missing-data handling is not reported in the registry record. There is no description of the extent or pattern of missing information, whether records with incomplete data were excluded, or whether any imputation or sensitivity analysis was used. For retrospective administrative data, missingness and incomplete linkage can affect which people or outcomes are represented; the record does not say whether these issues were assessed.
The analysis populations are also not defined in detail. Although enrollment is listed as 64882, the record does not provide analysis-specific denominators, inclusion criteria, or an accounting of exclusions. It is therefore not possible to determine from the registry record whether all enrolled records contributed to each outcome analysis. The record does not report interim analyses, stopping rules, or a detailed statistical analysis plan. These omissions limit assessment of selective reporting and the handling of incomplete or repeated observations.
12. What the Result Does, and Does Not, Mean
The study is designed to describe AKI epidemiology in England over 1998 to 2013, with emphasis on mortality after AKI and additional analyses by age group and calendar period. The registry record explains the intended questions and identifies a retrospective cohort design using national hospital-discharge and census data. It does not report the numerical findings needed to judge the direction, magnitude, or precision of the mortality trends.
Even if a trend estimate were available, an observational time trend would describe patterns in the analyzed records; it would not by itself establish that a particular change in clinical care caused the pattern. Changes in case identification, hospital coding, the population reaching hospital, or patient characteristics could contribute. The registry record does not report how these possible influences were measured or addressed.
The primary outcome concerns mortality during the hospital stay, described as an average of 15 days of follow-up. It does not, on the information in the registry record, describe longer-term mortality after discharge. The broader aims include incidence and determinants, but their results and operational definitions are not reported. The listed enrollment of 64882 should not be interpreted as the denominator for every outcome or as the number of events.
The record therefore supports conclusions about the study’s scope and design, but not claims that mortality improved or worsened, that a treatment was effective, or that any factor caused an outcome. Such conclusions require the actual results, their uncertainty, clear analysis denominators, and sufficient methodological detail. Those elements are not reported in the registry record.
13. Why This Trial Matters Statistically
National trend studies can address questions that a randomized trial is not designed to answer, such as how a condition and its associated outcomes are distributed across a population and over time. The stated aim to combine hospital-discharge data with census data reflects an effort to examine AKI beyond a single hospital or intervention group. The focus on both dialysis-requiring and non-dialysis-requiring AKI also makes case definition central to interpreting any trend.
Statistically, a trend is not just a sequence of counts. Its interpretation depends on the population at risk, the way cases and deaths are identified, and whether comparisons account for changes in patient mix and data collection. Age-group and period analyses can help describe patterns, but subgroup results need careful interpretation, particularly when many outcomes or comparisons are considered. The registry record does not report how these analytical issues were handled.
The record is also a useful reminder to separate a study’s stated question from its reported evidence. It lists enrollment of 64882 and describes a primary mortality outcome, yet does not report outcome estimates, denominators, or uncertainty. Those omissions prevent readers from assessing how much information the analyses contain or whether apparent differences are precise. The record identifies a potentially important epidemiological investigation, but statistical interpretation depends on results and methods beyond the brief registry description.
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 principal limitation for interpreting this record is that it does not report the study results. There are no mortality estimates, incidence estimates, subgroup findings, confidence intervals, or test results. The direction and magnitude of the trends cannot therefore be assessed from the registry record.
Several design details needed to evaluate validity are also not reported. These include eligibility criteria, the AKI case definition, the method for distinguishing dialysis-requiring from non-dialysis-requiring AKI, data-linkage procedures, and the handling of repeated hospital records. The record does not specify the analysis denominators or how deaths were identified. Although the primary follow-up is described as the hospital stay, with an average of 15 days, the range of follow-up and ascertainment after discharge are not reported.
The record does not describe whether analyses adjusted for age, severity, comorbidity, or other differences among patients, nor does it identify statistical models or uncertainty-estimation methods. Potential changes in coding and data capture over the period are not discussed. These matters are especially relevant to retrospective comparisons over calendar time, because changes in recorded cases need not reflect only changes in underlying disease occurrence or outcomes.
Enrollment is listed as 64882, but its relationship to the outcome-specific analysis populations is not explained. Missing-data procedures, multiplicity handling, protocol details, and the study’s own sample-size justification are not reported in the registry record. These gaps limit evaluation of selection, precision, and the possibility of selective emphasis among several outcomes and analyses.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Epidemiology of Acute Kidney Injury in England - 1998 to 2013 — NCT02216695.
- Registry record last updated 2016-12-09; status last verified 2016-12.
- Results first posted 2016-12-09.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
NCT02216695 is a completed retrospective cohort study titled “Epidemiology of Acute Kidney Injury in England - 1998 to 2013,” sponsored by University Hospitals of Derby and Burton NHS Foundation Trust. The registry record lists enrollment of 64882 and describes use of national hospital-discharge and census data to investigate AKI incidence, mortality, and determinants in England.
The primary outcome concerns secular trends in mortality after AKI, with follow-up during the hospital stay and an average duration of 15 days. Secondary outcomes address mortality by age group and five-year period. The record lists four outcome measures and five analyses. It does not report the outcome estimates, analysis denominators, detailed methods, or missing-data and multiplicity procedures. As a result, the study’s stated scope can be described, but its mortality findings and statistical precision cannot be evaluated from the registry record.