Perioperative Blood Pressures and Chronic Hypertension: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Perioperative Blood Pressures and Chronic Hypertension (NCT02136810), a registered phase not stated study. The primary outcome is Performance of Blood Pressure Referral Threshold.

2. Clinical Question

In plain terms, the question is about prediction and agreement between measurements taken in different settings, rather than whether one treatment changes blood pressure or another clinical outcome. The record also describes aims concerning patient perspectives on blood pressure control and lists secondary outcomes involving beliefs, adherence, and preidentified subgroups. Those additional aims do not change the meaning of the primary question: it concerns how often a clinic measurement classified as positive corresponds to the specified home blood pressure finding.

3. Trial Design

The registry identifies this as a completed study sponsored by Yale University, with enrollment of 200. Its title and summary describe an assessment of the association between home and clinic blood pressures among patients presenting for surgery. The brief summary also states an aim to measure the association between home blood pressures and patient perspectives on blood pressure control.

The record does not describe a randomized treatment assignment. Allocation is not stated, and the registry cautions that the listed groups are not a like-for-like control comparison. It is therefore more appropriate to understand the stated primary aim as evaluating a measurement-based prediction question than as estimating a randomized treatment effect. No specific observational design label is reported in the registry record.

The study began on 2015-11-09, and its primary completion date is 2017-01-11. Participants were followed for approximately 1 year according to the primary outcome timeframe. The record does not give further detail about visit schedules, the timing or number of clinic measurements, the home measurement schedule, or how the preadmission referral threshold was applied.

Of the 200 enrolled participants, 188 returned home blood pressure cuffs with valid blood pressure data for the primary outcome population. The reason valid data were unavailable for other participants, and whether any additional participants were excluded from particular analyses, are not reported in the registry record. The registry lists six outcome measures and no analyses. It does not describe a statistical analysis plan, the sample-size justification, interim analyses, or procedures for handling multiple outcomes. These omissions limit how much can be concluded about the intended analytical detail beyond the primary outcome description.

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: Of the 200 participants, 188 returned Home BP Cuffs with valid BP data.

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 Performance of Blood Pressure Referral Threshold, measured over Subjects followed for approximately 1 year.

The primary endpoint is the positive predictive value of preadmission testing-measured blood pressure for predicting mean home blood pressure >135/85mmHg. The registry says this value will be calculated and accompanied by a 95% confidence interval. The outcome is described as a proportion, and the stated primary population consists of the 188 participants who returned home blood pressure cuffs with valid blood pressure data.

General: Positive predictive value describes the proportion of people classified as positive by a test or threshold who also meet the defined target condition. In this study’s stated question, the clinic measurement is the predictor and the home blood pressure criterion is the target. A positive predictive value is useful for assessing a referral threshold because it speaks directly to how often a positive clinic classification corresponds to the specified home finding in the studied population.

The measure is not the same as sensitivity, specificity, or overall agreement. Those statistics answer different questions and are not identified as the primary endpoint in the record. Positive predictive value can also depend on the characteristics of the population in which it is measured, so its meaning is tied to the surgical patients and measurement procedures studied. The record does not report the actual positive predictive value, confidence interval, or the precise clinic cutoff used to define a positive result. Consequently, the endpoint’s intended interpretation is clear, but its estimated performance cannot be assessed from the registry results presented in the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does positive predictive value mean?

General: A predictive value starts with a classification made by a test or threshold and asks what is found among people receiving that classification. Positive predictive value focuses on positive classifications: it is the proportion of those classified as positive who meet the target definition. Here, the target is mean home blood pressure >135/85mmHg, and the predictor is preadmission testing-measured blood pressure. The measure therefore addresses a practical prediction question about the meaning of a positive clinic classification in the study population.

Positive predictive value should not be confused with sensitivity. Sensitivity asks how often a method identifies people who meet the target, including those the method may classify as negative. Specificity asks how often it classifies as negative those who do not meet the target. The registry names positive predictive value as the primary endpoint; it does not identify sensitivity or specificity as primary measures. A high or low predictive value alone would not describe every aspect of classification performance.

Why does the population matter?

General: Predictive values are population-dependent. The proportion of people in a study who meet the target condition affects the interpretation of positive classifications. For that reason, an estimate from surgical patients should be read in the context of the population and measurement process described by the study, rather than assumed to apply unchanged in other settings. The record identifies patients presenting for surgery and says the primary analysis population contains 188 participants with valid home blood pressure data. It does not describe the distribution of the target condition or provide the endpoint estimate, so neither can be evaluated from the record.

What does the confidence interval add?

General: An estimate from a sample is subject to sampling uncertainty. A confidence interval gives a range of values compatible with the observed data under the interval method’s assumptions. Its width is a guide to precision: a narrower interval indicates less sampling uncertainty than a wider interval, while neither width nor interval coverage resolves possible biases in measurement, selection, or analysis. The registry specifies a 95% confidence interval for the primary endpoint but does not report its limits or state the calculation method. Without the limits and point estimate, readers cannot judge precision.

A confidence interval is not a guarantee that the true value lies within a particular calculated interval, nor does it by itself show whether an estimate is important for a decision. Those interpretations require the numerical result and relevant context. No significance test or p-value for the primary endpoint is reported in the registry record.

What can be said about the analysis plan?

The endpoint description says the positive predictive value will be calculated. It does not specify the exact clinic threshold used, the handling of repeated measurements, the statistical model, or the confidence interval method. The record also does not report an adjustment strategy, an interim analysis plan, or a sample-size justification. These should not be inferred from the endpoint wording alone.

The registry lists no analyses. That is a statement about the analysis information entered in the record, not proof that no analyses were performed. Likewise, the presence of a planned endpoint does not establish that every analysis detail was prespecified. The registry record does not provide enough information to assess prespecification, analytic deviations, or robustness checks.

How should planning illustrations be understood?

General: Sample-size planning asks how many observations may be needed under specified assumptions to estimate an effect or detect a difference with a chosen level of statistical evidence and power. An illustration based on an observed effect is not an observed-power calculation and does not establish the original study’s design rationale. The planning assumptions described for this record use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect expressed as a fraction of the observed effect. These are planning assumptions, not evidence that the study was randomized or that the listed arms constitute a valid control comparison. The registry does not report the original sample-size justification, and the stated comparison limitations make a treatment-arm interpretation inappropriate.

Why does over-dispersion matter in general?

General: Over-dispersion occurs when variation in count data is greater than a statistical model assumes. If not addressed, standard errors can be too small and confidence intervals or tests can convey more precision than the data warrant. The primary outcome is described as a proportion, not a count-rate endpoint, and the record does not say that an over-dispersion model was used. This general issue should not be mistaken for a reported problem in this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures, including secondary outcomes concerning patient perspectives and beliefs, preidentified subgroups, and adherence. It does not report a multiplicity adjustment, a hierarchy among secondary outcomes, or a plan for controlling the chance of false-positive findings across multiple analyses. Those procedures are not reported in the registry record. The registry lists no analyses, so it also does not show which outcomes or comparisons were ultimately analyzed.

Multiplicity matters when several hypotheses are tested: considering many results can increase the chance that at least one appears notable by chance. General: A prespecified hierarchy or adjustment can help readers interpret a family of tests, but the appropriate approach depends on the scientific questions and analysis plan. No particular approach should be attributed to this study from the available record.

For missing data, the primary outcome description says 188 of the 200 participants returned home blood pressure cuffs with valid blood pressure data. The record does not state why valid data were unavailable for other participants, whether any other outcome data were missing, or whether missingness was handled by exclusion, imputation, or another method. It also does not report a sensitivity analysis assessing the effect of missing observations.

The stated primary population is therefore the group with valid home blood pressure data, but the record does not give further analysis-population definitions. It does not say whether all enrolled participants were included in secondary analyses or how subgroup populations were determined. These gaps matter because the target endpoint depends on usable home measurements, and readers cannot assess the influence of missing measurements without information about their frequency, causes, and handling.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry’s adverse-event entry lists 200 included participants and records zero serious adverse events, zero other adverse events, and zero deaths. These counts are the safety figures recorded for the included participants. The record does not list any serious adverse-event terms.

These entries should be read as registry-reported counts, not as a detailed account of safety surveillance. The record does not describe how adverse events were collected, the event definitions, the observation window for these counts, or the completeness of reporting. It also does not provide event-level descriptions or explain whether all participants had the same duration of safety follow-up. The primary outcome timeframe is approximately 1 year, but the record does not explicitly connect that timeframe to the adverse-event reporting period.

The safety population listed as 200 is distinct from the primary outcome population of 188 participants with valid home blood pressure data. The record does not explain whether the difference reflects cuff return, data validity, or another circumstance. The recorded zeros do not establish that no unrecorded events occurred; they indicate that the registry reports zero events in the listed categories. These figures also do not support a comparison of harms between treatments, because the study is not presented as a randomized comparison and no like-for-like control groups are identified.

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

The central statistical question is whether preadmission clinic blood pressure predicts mean home blood pressure above the stated threshold among surgical patients. The registry describes a positive predictive value as the primary measure and identifies a 95% confidence interval as the intended precision summary. However, neither the estimate nor its interval is reported in the registry record. The posted information therefore cannot establish how often a positive clinic classification corresponded to the home blood pressure criterion or how precisely that relationship was estimated.

The record does show that 200 participants were enrolled and that 188 returned home blood pressure cuffs with valid data for the primary outcome population. This describes the available population for the stated endpoint, but does not explain why valid data were unavailable for other participants. It also does not show the clinic threshold applied or the distribution of positive and negative classifications.

General: A predictive association is not necessarily evidence that one measurement causes another, or that changing how a measurement is obtained changes a patient outcome. Predictive value concerns classification within a population and measurement process. This study’s registry description does not report a randomized intervention or a treatment contrast, and it cautions that the groups are not like-for-like controls. The primary result, even if reported, would need to be interpreted as a measurement-prediction finding rather than a causal treatment effect.

The registry also lists aims related to patient perspectives, beliefs, adherence, and preidentified subgroups, but does not report their results or analysis details. No conclusions about those relationships can be drawn from the stated aims alone. Likewise, the listed zero adverse-event counts do not provide a comparative safety assessment.

In short, the record defines a clinically interpretable statistical question and identifies the size of the enrolled and primary outcome populations. It does not provide the result needed to answer that question. It therefore supports understanding what the investigators intended to measure, but not a conclusion about the observed predictive performance, its precision, or its applicability beyond the described study population.

13. Why This Trial Matters Statistically

This study is statistically interesting because it treats blood pressure measurement as a prediction problem across settings. Clinic and home measurements are not interchangeable by definition; the stated research question asks whether a preadmission measurement can identify participants meeting a home-measurement criterion. Positive predictive value is directly relevant to that classification question because it focuses on the proportion of positive clinic classifications that correspond to the specified home finding.

The endpoint also illustrates why the numerical result and its uncertainty are both needed. A positive predictive value without a confidence interval gives limited information about precision, while an interval without the estimate is not enough to understand the observed performance. The registry names both as planned reporting elements, but does not report either value.

The study highlights the importance of clearly defining the analysis population. The primary outcome population includes 188 participants with valid home blood pressure data, while enrollment was 200. Without details about unavailable measurements and their handling, readers cannot evaluate how the analyzed group may differ from the enrolled group. This is a general concern for studies in which an endpoint depends on completion and validity of a measurement procedure.

Finally, the registry distinguishes an association question from a randomized treatment comparison. That distinction matters because predictive performance does not, by itself, establish a causal effect. The record’s warning that groups are not a like-for-like control comparison reinforces the need to interpret the study as a measurement-focused investigation. Its value as a statistical question is apparent, but the missing endpoint results and analysis details prevent assessment of the study’s actual predictive findings.

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 primary limitation for interpreting the result is that the registry does not report the positive predictive value or its 95% confidence interval. Without those statistics, neither observed performance nor precision can be assessed. The exact preadmission clinic threshold used to define a positive result is also not stated in the endpoint description.

The primary outcome population is described as 188 participants with valid home blood pressure data, compared with 200 enrolled participants. The record does not explain why valid measurements were unavailable for some participants, whether missingness was related to clinic or home blood pressure, or how missing data were handled. These omissions limit evaluation of possible selection effects.

The record does not detail how clinic or home blood pressure measurements were obtained, how many measurements contributed to each mean, or how measurement quality was assessed. It also does not report the statistical method for calculating the confidence interval, whether any adjustment was used, or whether prespecified sensitivity analyses were conducted. The sample-size justification and interim analysis plan are not reported in the registry record.

Although six outcome measures are listed, no analyses are listed, and multiplicity procedures are not described. Results for the secondary aims and preidentified subgroups are not reported in the registry record. The safety entry records zero events in the listed categories, but provides no further detail about event collection or the safety observation period.

The registry cautions that this is not a randomized comparison and that the groups are not a like-for-like control comparison. As a result, the record does not support a treatment-effect interpretation. These limitations concern what can be evaluated from the registry record; they do not establish that the unreported procedures or results do not exist elsewhere.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Perioperative Blood Pressures and Chronic Hypertension — NCT02136810.
• Registry record last updated 2023-06-05; status last verified 2023-06.
• Results first posted 2018-12-14.
• 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 record describes a completed Yale University study of the association between home and clinic blood pressures among patients presenting for surgery. Enrollment was 200. The primary outcome is the positive predictive value of preadmission testing-measured blood pressure for predicting mean home blood pressure >135/85mmHg, with a planned 95% confidence interval. The primary outcome population includes 188 participants with valid home blood pressure data.

The study also aimed to examine patient perspectives on blood pressure control and lists secondary outcomes concerning beliefs, subgroups, and adherence. The registry lists six outcome measures and no analyses. It does not report the primary estimate, confidence interval, detailed analysis methods, or sample-size justification. The adverse-event entry records zero serious adverse events, zero other adverse events, and zero deaths among 200 included participants. The record does not describe a randomized comparison and cautions that groups are not like-for-like controls.