The Impact of Vitamin D on Tuberculosis Among Koreans: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Impact of Vitamin D on Tuberculosis Among Koreans (NCT01137370), a registered phase not stated study. The primary outcome is Prevalence of Vitamin D Deficiency.

2. Clinical Question

The registry describes a study of tuberculosis and vitamin D among Koreans, with the stated aim of examining vitamin D deficiency in relation to tuberculosis development and treatment outcomes. It also states an aim to evaluate whether vitamin D receptor gene genotypes are associated with tuberculosis development. The primary outcome listed in the record is the prevalence of vitamin D deficiency at enrollment.

The registry’s broader aims concern tuberculosis development and treatment response, but the listed primary outcome is a prevalence measure at enrollment. The record does not specify how vitamin D status, gene variants, tuberculosis development, or treatment response were to be related analytically. It also does not report a result that would answer those broader aims. Accordingly, the primary question can be described from the registry, while the magnitude and precision of any association cannot be assessed from the reported information.

3. Trial Design

The registry record identifies the study as NCT01137370, titled The Impact of Vitamin D on Tuberculosis Among Koreans. Seoul National University Hospital is listed as sponsor. The study began in 2010-01, had primary completion in 2011-03, and is marked COMPLETED. Enrollment is listed as 203. These registry entries describe the study record; they do not establish how many participants were included in each group or in each analysis.

The arm labels are Patients with TB and People without TB. Their descriptions are blank. The registry characterizes the study as not a randomized comparison, and allocation is not stated. The groups are defined by tuberculosis status rather than by an assigned treatment in the arm descriptions, so a difference between them cannot automatically be interpreted as a treatment effect. Details of recruitment, eligibility, setting, and follow-up are not reported in the registry record.

The primary outcome is Prevalence of Vitamin D Deficiency, with a timeframe of at enrollment and a unit listed as participants, %. The registry lists two outcome measures but does not provide their names or results beyond the primary outcome information in the record. It lists zero analyses. This does not establish that no analysis was performed; it means that analyses are not reported in the registry record.

The record does not state a sample-size justification, an allocation procedure, or a detailed statistical analysis plan. It also does not give group-specific enrollment or analysis counts. Consequently, the design can be described only at the level of the registry’s study status, stated aims, arm labels, and listed outcome. Further methodological detail is not reported in the registry record.

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.

Before assignment: Korean who had been abroad for longer than 1 month during the previous year and non-Koreans were excluded from both arms.

Overall Study

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 Prevalence of Vitamin D Deficiency, measured over At enrollment.

The primary endpoint is the prevalence of vitamin D deficiency at enrollment. Its listed unit is participants, %. In general, prevalence describes the proportion of a defined population that has a specified condition at a particular time. For this outcome, interpretation depends on how vitamin D deficiency is defined, which participants are included in the denominator, and how missing measurements are handled. Those details are not reported in the registry record.

A prevalence measure is relevant to the study’s stated focus on vitamin D deficiency among people with and without tuberculosis. It can describe how common the defined deficiency is within a group at enrollment. By itself, however, a prevalence estimate does not establish whether deficiency preceded tuberculosis, whether it contributed to disease development, or whether it predicts treatment response. Those questions require appropriate timing, measurements, and analyses, which are not detailed in the record.

The registry does not report a numerical prevalence, group-specific counts, an estimate comparing the groups, or a measure of uncertainty for this endpoint. It also does not identify the threshold used to classify deficiency. Thus, the endpoint’s intended meaning is clear at a broad level, but its operational definition and observed result cannot be evaluated from the information reported.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The methods information in the registry is limited. The study is not described as a randomized comparison, allocation is not stated, the outcome description gives only the primary measure and its timeframe, and the record lists zero analyses. The statistical explanations below are general, and do not imply that a particular method was used in this study.

What does a prevalence endpoint represent?

In general, prevalence is the proportion of a specified population that meets a defined condition at a specified time or period. To interpret it, an analysis needs a rule for classifying the condition and a clear definition of the population included. Here, the endpoint is vitamin D deficiency at enrollment, but the threshold for deficiency and the analysis denominator are not reported in the registry record. The listed unit, participants, %, indicates that the intended outcome is expressed as a count and percentage, but does not give the observed count or percentage.

If prevalence is reported separately for the tuberculosis and non-tuberculosis groups, the comparison would describe how the measured condition differs between those groups at enrollment. In general, such a contrast is descriptive unless the design and analysis justify a stronger interpretation. Because the groups are defined by tuberculosis status and the comparison is not randomized, a difference would not by itself demonstrate that vitamin D deficiency caused tuberculosis or that tuberculosis caused deficiency.

How should uncertainty be read?

In general, a point estimate is an estimate of the quantity of interest, while a confidence interval communicates its statistical uncertainty under stated assumptions. A narrow interval indicates greater precision than a wide interval, but precision is not the same as freedom from bias. An interval can be precisely estimated around a result affected by selection, measurement error, or confounding. No point estimate or confidence interval for the primary outcome is reported in the registry record, so neither the estimate nor its precision can be evaluated.

A p-value, when used, describes how unusual data at least as incompatible with a specified null hypothesis would be under the model and assumptions. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The registry record does not report a p-value or a hypothesis-testing analysis for the primary outcome. No inferential result should be inferred from the fact that the study is marked completed.

What can group comparisons establish?

In general, randomized allocation can help balance measured and unmeasured factors between treatment groups, while nonrandomized group comparisons may be affected by differences in participant characteristics or circumstances. The record says this is not a randomized comparison and does not state allocation. Its arm labels identify patients with tuberculosis and people without tuberculosis. A statistical comparison between such groups could describe an association, but causal claims would require additional design and analysis support. Adjustment for confounding can address measured factors under appropriate assumptions, but cannot guarantee that all sources of bias have been removed. Covariates, adjustment methods, and model specifications are not reported in the registry record.

The outcome is described as a count-type measure rather than as a single effect estimate. In general, counts may be analyzed using methods suited to their distribution and the way observations are collected. Over-dispersion occurs when count variability exceeds what a simple model expects; ignoring it can make uncertainty estimates too small. Whether over-dispersion is relevant depends on the actual data and model. The registry record does not report a count model or enough outcome detail to determine what statistical model would be appropriate. No claim is made that a particular count model was used.

What do the planning assumptions mean?

The registry’s sample-size assumptions describe planning illustrations based on the observed effect, rather than the study’s own design justification. They specify a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. For time-to-event calculations, the stated convention is a total number of events using the Schoenfeld approach; other calculations are expressed as participants per arm. These are assumptions for planning illustrations, not evidence that the original study used those design parameters.

In general, a sample-size calculation estimates the amount of information needed to detect an effect under stated assumptions. It depends on the chosen effect, variability or event rate, error threshold, and desired power, among other considerations. A calculation based on an observed effect is retrospective and can be unstable, particularly when the original estimate is imprecise. Such planning values are not observed power and do not establish the chance that the study detected a true effect. The observed effect and numerical planning results are not reported in the registry record, so their values cannot be interpreted in this account.

More generally, a statistical method must match the outcome, design, and question. A descriptive prevalence estimate, an association between groups, and a causal effect are different targets. The registry provides too little analysis detail to determine which estimand or model was used for outcomes beyond naming the primary endpoint. Details of model assumptions, diagnostics, handling of repeated observations, covariates, and uncertainty estimation are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures, but only the primary endpoint is described in the record. It does not identify the other outcome or report results for either outcome. The record also lists zero analyses. Therefore, the analysis populations, model specifications, and any planned hierarchy among outcomes are not reported in the registry record.

Multiplicity arises in general when researchers test or estimate several outcomes, subgroups, exposures, or contrasts. When many inferential tests are conducted, the chance of at least one apparently notable result can increase. Statistical approaches can control or account for this, but the appropriate approach depends on which questions were prespecified and how they relate. The registry record does not report a multiplicity strategy, so no adjustment or control procedure can be attributed to this study.

Missing data can affect both the denominator and the interpretation of a prevalence estimate. In general, missingness may be related to participant characteristics or outcome status, and different assumptions about missing observations can lead to different estimates. The record does not report the amount or pattern of missing vitamin D measurements, missing gene data, or missing outcome data. It also does not describe an imputation method, complete-case analysis, or sensitivity analysis. This means missingness cannot be evaluated; it does not establish that all measurements were complete.

The record does not identify an intention-to-treat, per-protocol, or other analysis population. Those labels are commonly used in randomized intervention studies, and their relevance depends on the design and question. Since this record describes a nonrandomized comparison and does not report analysis details, the population used for any result is not reported in the registry record. No assumptions should be made about how exclusions or incomplete records were handled.

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

The registry establishes that a study was conducted with the stated aim of examining vitamin D deficiency and tuberculosis among Koreans. It identifies patients with tuberculosis and people without tuberculosis as the groups, lists enrollment as 203, and gives the prevalence of vitamin D deficiency at enrollment as the primary outcome. These details describe the research question and its registry record, not a finding about how common deficiency was.

The record does not report the primary outcome value, group-specific results, uncertainty estimates, or a statistical test. It therefore does not support a conclusion about the direction or size of a difference between the groups. It also does not provide the result needed to assess its precision. A completed status indicates the registry’s study status; it does not substitute for outcome data or an analysis.

Even if a group difference were reported, its meaning would depend on the definition of deficiency, the participants included, the quality of measurement, and the statistical analysis. In general, a nonrandomized comparison between groups defined by tuberculosis status can identify an association but cannot by itself establish cause and effect. The record does not report adjustment methods or other evidence that would allow causal interpretation.

The stated aims concerning tuberculosis development, treatment response, and vitamin D receptor gene variants are broader than the primary endpoint described. The record does not provide results for those aims. The posted information consequently does not establish whether vitamin D status or genotype is associated with disease development or treatment response, and it does not support a treatment recommendation. Its statistical meaning is limited to documenting the study’s aims, groups, timing, and registered primary outcome while leaving the outcome findings and analysis unavailable in the registry record.

12. Why This Trial Matters Statistically

This study raises several distinct statistical questions that are useful to keep separate. The primary endpoint is prevalence at enrollment, while the stated scientific aims also concern tuberculosis development and treatment response. A cross-sectional prevalence measure and a question about development or response require different interpretations and may require different timing and analysis. The registry record does not report the additional methods or results needed to connect those aims.

The group labels also matter. Patients with tuberculosis and people without tuberculosis are not described as randomized treatment arms. In general, comparisons between disease-status groups can be affected by differences in participant characteristics, selection, and measurement. Recognizing that distinction helps prevent a descriptive association from being mistaken for a treatment effect or causal conclusion.

Clear endpoint definitions are central to reproducible biostatistics. Here, the registry names vitamin D deficiency but does not report the threshold used to define it or the denominator and missing-data rules. These details affect how a prevalence estimate would be constructed and compared. Reporting estimates alongside uncertainty and analysis methods would allow readers to assess both magnitude and precision.

The record also illustrates the difference between a completed study and a fully interpretable statistical result. It records enrollment, dates, status, and the primary outcome label, but does not report analyses or outcome findings. For clinical researchers, that distinction is important: design information can explain what a study intended to examine, while the estimate and its uncertainty are necessary to evaluate what the data show. In this case, the registry record allows the question to be identified but does not provide the statistical results needed to answer it.

13. 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.

Several trial-specific limitations of interpretation follow directly from the registry information. First, the primary outcome is named but not numerically reported. There is no prevalence estimate, count, group-specific denominator, confidence interval, or p-value in the registry record. Consequently, the endpoint’s magnitude and precision cannot be evaluated.

Second, the operational definition of vitamin D deficiency is not reported. Without the threshold and measurement details, readers cannot determine how participants were classified or whether the definition is comparable with other studies. The record also does not explain how incomplete vitamin D measurements or other missing data were handled.

Third, the arm descriptions are blank, while the arm labels distinguish patients with tuberculosis from people without tuberculosis. The record states that the comparison is not randomized and does not state allocation. Detailed eligibility criteria, recruitment methods, group-specific counts, and participant characteristics are not reported. These omissions limit assessment of comparability, selection, and generalizability.

Fourth, the stated aims include vitamin D receptor gene variants, disease development, and treatment response, but the record does not report the methods or results for those questions. It lists two outcome measures and zero analyses, but does not provide a complete account of outcome definitions, analysis populations, model choices, confounder adjustment, or multiplicity handling. The registry record also does not state a sample-size justification or interim-analysis plan. These are limits on what can be concluded from the record, not proof that such procedures were absent from the research itself.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: The Impact of Vitamin D on Tuberculosis Among Koreans — NCT01137370.
• Registry record last updated 2014-02-24; status last verified 2014-01.
• Results first posted 2014-02-24.
• 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.

17. Record Summary

NCT01137370 is a completed study titled The Impact of Vitamin D on Tuberculosis Among Koreans, sponsored by Seoul National University Hospital. The registry lists enrollment of 203, a start date of 2010-01, and primary completion in 2011-03. Its stated aims concern vitamin D deficiency, tuberculosis development and treatment outcomes, and vitamin D receptor gene variants.

The listed groups are patients with tuberculosis and people without tuberculosis. The primary outcome is prevalence of vitamin D deficiency at enrollment. The comparison is not randomized, and allocation is not stated. The registry lists two outcome measures and zero analyses, but does not report the primary outcome result, group-specific estimates, or statistical uncertainty. The deficiency threshold, analysis populations, missing-data procedures, and detailed statistical methods are not reported in the registry record. The available record therefore identifies the study question and design features, but does not provide findings with which to assess the outcome.