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 Blue Sky Study: Impact of Milk and Vitamin D for Child Growth and Health (NCT00886379), a randomized phase 2 study. The primary outcome is Serum 25-hydroxyvitamin D Concentrations in Schoolchildren.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00886379 |
| Phase | Phase 2 |
| Condition | Vitamin d Deficiency |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 597 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Brigham and Women's Hospital |
| Results posted | Yes |
2. Clinical Question
Population
The study concerned Mongolian schoolchildren. The registry record does not report further eligibility details or a more specific description of the analyzed population.
Intervention
The listed interventions were Mongolian milk without vitamin D, Mongolian milk with vitamin D, UHT milk, a milk substitute, seasonal vitamin D supplements, and daily vitamin D supplements. The arm descriptions name the milk products and supplement schedules, but do not give doses or administration details.
Comparator
The trial included multiple intervention arms. The registry record does not specify a single comparator for the primary endpoint or describe which pairwise contrasts were planned.
Primary question
The listed primary outcome was serum 25-hydroxyvitamin D concentration in schoolchildren, with blood analyzed at day 0 and day 49. Numerical concentrations and between-arm comparisons are not reported in the registry record, so the direction and precision of any differences cannot be described.
The study's brief summary describes a broader set of intended health and growth topics, including growth, vitamin D levels, insulin-like growth factor 1, growth hormone, academic attention, respiratory infections, asthma, and flexural dermatitis. That description gives context for the study's aims, but it does not supply results for those outcomes. The listed primary outcome is a laboratory measure rather than a direct measure of growth, symptoms, or functioning. The registry record does not explain the primary endpoint's role relative to the other topics in the summary.
The central statistical question is therefore limited: how serum 25-hydroxyvitamin D concentrations were measured at the stated time points and what comparisons the study intended to make. The posted record does not provide the estimates needed to answer how concentrations changed or whether groups differed. It also does not state a specific primary contrast, so the intended comparison cannot be inferred from the intervention list alone.
3. Trial Design
The Blue Sky Study is identified as a Phase 2, randomized, double-blind, parallel intervention study. The registry lists an enrollment of 597 and a completed status. Brigham and Women's Hospital is listed as the sponsor. The recorded study start is 2009-01, and primary completion is recorded as 2009-03.
A randomized design assigns participants to study groups by chance, which can help balance participant characteristics across groups. In general, double masking means that some people involved in the study are unaware of assigned treatment; the registry record does not specify which people were masked or how masking was maintained. A parallel design means that groups are compared across the study period rather than participants all receiving a sequence of different interventions. These are general descriptions of the design terms, not additional details about this trial's procedures.
Six interventions and six arm descriptions appear in the record. They include milk products with and without vitamin D, a milk substitute, and seasonal or daily vitamin D supplements. The record does not report the number allocated to each intervention, the allocation ratio, the randomization method, or whether all listed interventions were compared directly with one another. Safety information lists five groups; the record does not explain that difference from the six interventions listed elsewhere.
The primary outcome timeframe states that blood was analyzed at day 0 and day 49. The record does not describe the study sites, participant ages, eligibility criteria, adherence procedures, or whether the stated timeframe applied identically to every intervention arm. It also does not report a protocol-level statistical plan, including a sample-size justification or the planned analysis model. Such details cannot be inferred from the design labels or enrollment figure.
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 | Unfortified Mongolian Milk | Fortified Mongolian Milk | Fortified UHT Milk | Daily Vitamin D Supplements | Seasonal Vitamin D Supplements |
|---|---|---|---|---|---|
| STARTED | 104 | 143 | 143 | 112 | 95 |
| COMPLETED | 101 | 140 | 137 | 109 | 92 |
| NOT COMPLETED | 3 | 3 | 6 | 3 | 3 |
Reasons for not completing this period:
| Reason | Unfortified Mongolian Milk | Fortified Mongolian Milk | Fortified UHT Milk | Daily Vitamin D Supplements | Seasonal Vitamin D Supplements |
|---|---|---|---|---|---|
| Transferred Schools | 0 | 0 | 2 | 1 | 1 |
| Final blood draw not obtained | 3 | 3 | 4 | 2 | 2 |
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 | Unfortified Mongolain Milk | Fortified Mongolian Milk | Fortified UHT Milk | Daily Vitamin D Supplements | Seasonal Vitamin D Supplements | Total |
|---|---|---|---|---|---|---|---|
| Participants analysed | 101 | 140 | 137 | 109 | 92 | 579 | |
| Age, Categorical: <=18 years | Participants | 101 | 140 | 137 | 109 | 92 | 579 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 | 0 | 0 | 0 | 0 | 0 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 | 0 | 0 | 0 |
| Sex: Female, Male: Female | Participants | 51 | 65 | 69 | 45 | 41 | 271 |
| Sex: Female, Male: Male | Participants | 50 | 75 | 68 | 64 | 51 | 308 |
6. Primary Endpoint
The registry lists the primary outcome as Serum 25-hydroxyvitamin D Concentrations in Schoolchildren, measured over Blood was analyzed at day 0 and day 49.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | ng/ml |
| Endpoint classification | Continuous Endpoint |
The listed primary endpoint is serum 25-hydroxyvitamin D concentration in schoolchildren, expressed in ng/ml. The description identifies the analyte as 25(OH)D3 and says it was measured by liquid chromatography-tandem mass spectrometry. The stated timeframe is blood analysis at day 0 and day 49. The endpoint is described as a mean with standard deviation as the dispersion measure.
As general background, 25-hydroxyvitamin D is a blood measure used to assess vitamin D status. Measuring a biological marker can show whether groups have different marker concentrations at specified time points. A mean describes the central value in a group, while a standard deviation describes variation among individual measurements around that mean. Those summaries do not, on their own, describe every participant's value or establish the clinical importance of a difference.
The registry record does not report the actual means, standard deviations, changes from baseline, or contrasts between intervention arms. Although the timeframe names two measurements, the primary outcome is not reduced in the record to a single comparison across those time points. The numerical size, direction, and precision of any change therefore cannot be interpreted from the posted results.
The brief summary also names other biological, growth, and health topics. They provide context but do not substitute for the numerical results of the listed primary endpoint. The registry record does not report outcome values for those topics in the information.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies serum 25-hydroxyvitamin D concentration as the primary outcome and specifies blood analysis at day 0 and day 49. It does not report numerical outcome values, standard deviations, estimates of change, confidence intervals, or tests of differences between groups. Consequently, the posted results do not establish the direction or magnitude of any change or between-group contrast, and their statistical precision cannot be assessed.
The record lists one outcome measure, but the endpoint includes more than one time point and the record notes that it has several categories or time points and is not reduced to one comparison. This matters because a mean at one time point, a change over time, and a comparison of changes between groups are different statistical quantities. Without reported estimates and a clear contrast, they cannot be treated as interchangeable or reconstructed from the design description.
The study's randomized and double-blind labels describe design features, not results. Randomization can support comparisons by reducing systematic differences at assignment, but it does not itself show what happened to the endpoint. Likewise, a stated laboratory method identifies how the biomarker was measured but does not supply an estimate of measurement variability or a treatment contrast.
The safety listing records zero serious adverse events, zero other adverse events, and zero deaths in each of the five groups shown in that listing. These are registry counts for the stated groups and should be read as recorded counts, not as proof that no harm was possible or that every type of event was assessed identically. The record does not provide event descriptions in the serious-event terms list.
There are no analysis results listed in the registry record. The record therefore cannot support a claim about statistical significance, an effect size, or a clinically meaningful difference. A non-reported estimate is not evidence that groups were equal. For the same reason, the absence of a reported confidence interval does not indicate that an effect was precise; it means that precision cannot be judged from this record.
9. Statistical Methods Explained
The design and endpoint labels give some statistical context, but the registry record does not report the analysis methods used for the primary outcome. It identifies the endpoint as a continuous measure summarized by a mean and standard deviation, and gives two blood collection time points. The record lists zero analyses. The following explanations describe general statistical concepts and do not claim that a particular method was used in this study.
What does a mean and standard deviation describe?
For a continuous measurement such as a blood concentration, the mean is an average that describes the center of the observations. The standard deviation describes how spread out the individual observations are around that average. These summaries answer different questions: the mean concerns the central level, while the standard deviation concerns variation among participants. Neither one alone gives the uncertainty in a comparison between groups. The registry record does not include the outcome means or standard deviations needed to interpret this endpoint numerically.
How do time points affect the comparison?
When an outcome is measured at baseline and follow-up, several analyses are possible in general. Investigators might report follow-up values by group, changes within each group, or a between-group contrast in change. Those quantities have different interpretations and can yield different estimates. A statistical plan may also specify an adjusted comparison, but the registry record does not say whether the study used adjustment or which of these approaches was intended. Because the record notes several categories or time points without reducing them to one comparison, no single estimand should be assumed.
What does randomization contribute?
In general, random assignment is intended to make groups comparable at the start of a trial, on average. It does not guarantee identical groups in every realized trial, and it does not remove the need for an appropriate analysis. The record does not describe sequence generation, concealment of assignments, allocation ratios, or group sizes. It also does not provide baseline values by arm. The design label alone is not enough to evaluate the success of the assignment process or the balance of measured characteristics.
What can a confidence interval tell a reader?
In general, a confidence interval communicates uncertainty around an estimated quantity. A narrower interval indicates greater statistical precision than a wider interval for the same kind of estimate. Its interpretation depends on which contrast was estimated and how the interval was calculated. No interval or primary-outcome estimate is reported in the registry record, so the precision of any treatment comparison cannot be evaluated. A p-value, even if reported, would not by itself describe the size or practical importance of an effect; the record does not list p-values for the endpoint.
What is over-dispersion, and does it apply?
As general background, over-dispersion refers to more variability in data than an assumed statistical model allows. It is most often discussed for outcomes such as counts or event rates, where a model's variance assumptions affect uncertainty estimates. The listed primary endpoint is a continuous concentration summarized by a mean and standard deviation, not a count outcome. The registry record does not describe a model or any variance diagnostics, so there is no basis to say whether over-dispersion was considered or relevant to a particular analysis.
How should planning illustrations be understood?
General sample-size planning asks how many participants may be needed to detect a specified effect under stated assumptions. The record describes a planning illustration based on a fraction of an observed effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also specifies that the illustration gives participants per arm for non-time-to-event outcomes. Such assumptions describe a planning exercise, not the trial's actual allocation or observed power. The registry record does not report the numerical outcome estimates needed to assess an observed-effect-based illustration, nor does it state that these were the assumptions used to design the trial.
The record does not state the primary analysis model, the handling of repeated measurements, covariate adjustment, inferential test, confidence-interval method, or any interim analysis plan. These details are not reported in the registry record and should not be inferred from a general description of trial design.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity arises when investigators assess several outcomes, time points, treatment contrasts, or subgroups. In general, conducting many statistical tests can increase the chance that at least one result appears unusual by chance. A statistical plan may address this through a prespecified hierarchy or an adjustment, but the registry record does not report a multiplicity strategy or identify the planned primary contrasts.
The study summary names a broad set of health and growth topics, while the listed primary outcome concerns serum 25-hydroxyvitamin D concentration at day 0 and day 49. The record lists one outcome measure but notes that its categories or time points are not reduced to a single comparison. It does not identify whether each time point or intervention comparison was treated as a separate test, or whether any adjustment was planned. Therefore, the extent of multiplicity and its handling cannot be evaluated from the registry record.
Missing-data methods are also not reported. The record does not give the number of participants with a primary-outcome measurement at either time point, reasons for missing measurements, or a method for handling incomplete data. It is not possible to determine whether all enrolled participants contributed to the endpoint analysis.
The analysis populations are not described in the registry record. In particular, it does not say whether results were intended for all randomized participants, participants who followed the assigned intervention, or another defined group. These distinctions matter because excluding participants after randomization can affect how comparisons are interpreted. The registry record also does not provide analysis results with which to check how the chosen population or missing-data approach affected the estimates.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Unfortified Mongolain Milk | 0 | 101 | 0.0% |
| Fortified Mongolian Milk | 0 | 140 | 0.0% |
| Fortified UHT Milk | 0 | 137 | 0.0% |
| Daily Vitamin D Supplements | 0 | 109 | 0.0% |
| Seasonal Vitamin D Supplements | 0 | 92 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Unfortified Mongolain Milk | 0 of 101 |
| Fortified Mongolian Milk | 0 of 140 |
| Fortified UHT Milk | 0 of 137 |
| Daily Vitamin D Supplements | 0 of 109 |
| Seasonal Vitamin D Supplements | 0 of 92 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Unfortified Mongolain Milk | 0 of 101 |
| Fortified Mongolian Milk | 0 of 140 |
| Fortified UHT Milk | 0 of 137 |
| Daily Vitamin D Supplements | 0 of 109 |
| Seasonal Vitamin D Supplements | 0 of 92 |
The safety listing gives five groups and records serious adverse events, other adverse events, and deaths separately. For unfortified Mongolian milk, the counts are 0 serious adverse events among 101 at risk, 0 other adverse events among 101 at risk, and 0 deaths. For fortified Mongolian milk, the corresponding counts are 0 among 140 at risk for serious events, 0 among 140 for other events, and 0 deaths. For fortified UHT milk, the counts are 0 among 137 at risk in each adverse-event category and 0 deaths.
For daily vitamin D supplements, the listing records 0 serious adverse events among 109 at risk, 0 other adverse events among 109 at risk, and 0 deaths. For seasonal vitamin D supplements, it records 0 serious adverse events among 92 at risk, 0 other adverse events among 92 at risk, and 0 deaths. These are counts in the registry record; they are not estimates of comparative risk, and no uncertainty intervals or event-specific details are reported.
The serious-event terms list is empty. The record does not explain the difference between five groups in the safety listing and six interventions elsewhere. Zero recorded events should not be interpreted as proof that risk was absent, particularly without further information about event definitions, monitoring, and completeness of reporting.
12. What the Result Does, and Does Not, Mean
The record establishes that a randomized, double-blind, parallel Phase 2 study was conducted with milk products and vitamin D supplement interventions, and that serum 25-hydroxyvitamin D concentration was the listed primary endpoint. It also states that blood was analyzed at day 0 and day 49. These are design and measurement details; they are not evidence about the direction or size of an intervention effect.
Numerical primary-outcome results and statistical analyses are not reported in the registry record. No conclusion can be drawn from this record about whether concentrations changed, whether groups differed, how large any difference was, or how precisely it was estimated. The absence of numerical results must not be mistaken for a finding of no difference. Nor can a p-value or confidence interval be inferred from the sample size or study design.
The safety counts are recorded as zero for serious adverse events, other adverse events, and deaths in each group listed. Those counts describe what the registry reports for those categories and groups. They do not establish that every possible adverse event was captured or that an intervention is free of risk.
The study's brief summary indicates that it addressed more than the listed primary outcome, including growth and several health topics. The registry record does not report numerical findings for those topics in the information. Consequently, its stated aims should not be confused with demonstrated outcomes. This statistical interpretation is confined to what the record reports, and it cannot replace results that are not reported there.
13. Why This Trial Matters Statistically
This trial is statistically notable as a multi-arm randomized study with several milk and vitamin D interventions, while its listed primary outcome is a continuous laboratory measure assessed at two time points. That combination raises important questions about which groups were compared, how changes over time were defined, and how several possible contrasts were handled. The registry record does not give enough analysis detail to answer those questions, illustrating why a design label and an endpoint name alone are not a complete statistical report.
Randomization and masking are relevant design features, but interpretation also requires outcome estimates, uncertainty measures, and a clear account of the analysis population. Without the reported means, standard deviations, contrasts, and confidence intervals, readers cannot judge the magnitude or precision of any endpoint difference. The record also does not describe missing measurements or the planned handling of multiple outcomes and time points.
The trial's broad summary includes biological, growth, and health topics, whereas its listed primary outcome focuses on serum 25-hydroxyvitamin D concentration. In general, a biomarker can help characterize biological status, but it is distinct from direct clinical or functional outcomes. The record does not provide numerical results that would allow readers to assess either the biomarker endpoint or the other topics named in the summary.
Finally, the safety listing is useful as a record of event counts, but its zero counts need context about ascertainment and reporting. Taken together, the available information illustrates a basic statistical principle: a trial's design and planned measurements do not by themselves establish an effect. Transparent estimates, uncertainty, and analysis details are needed to evaluate what the trial's data show.
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 trial from the registry record is the absence of numerical results for its listed primary endpoint. Means, standard deviations, changes from baseline, between-group estimates, confidence intervals, and p-values are not reported. The record lists zero analyses, so the size, direction, and precision of the endpoint findings cannot be assessed.
The endpoint timeframe includes day 0 and day 49, but the registry record notes several categories or time points and does not reduce the outcome to a single comparison. It does not identify the primary contrast, the method for handling repeated measurements, or whether adjusted estimates were planned. This leaves the target of inference unclear.
The record lists six interventions and arm descriptions, whereas the safety information lists five groups; no explanation is reported. It also does not specify the allocation ratio, participants assigned to each arm, participant eligibility details, or analysis populations. Missing outcome data and the methods used to address them are not reported. The statistical plan, including any multiplicity approach or interim analyses, is not reported in the registry record.
The safety counts are limited to the categories and groups listed. The record gives no serious-event terms and does not describe event definitions, monitoring procedures, or completeness of ascertainment. These omissions limit what can be concluded from zero recorded counts. The listed study aims extend beyond the primary endpoint, but numerical results for the broader topics are not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Blue Sky Study: Impact of Milk and Vitamin D for Child Growth and Health — NCT00886379.
- Registry record last updated 2021-03-23; status last verified 2021-02.
- Results first posted 2021-03-23.
- 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.
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18. Record Summary
The Blue Sky Study (NCT00886379) is listed as a completed, randomized, double-blind, parallel Phase 2 study sponsored by Brigham and Women's Hospital. The recorded enrollment is 597. The study start is recorded as 2009-01, and primary completion as 2009-03.
The interventions include Mongolian milk with and without vitamin D, UHT milk, a milk substitute, and seasonal or daily vitamin D supplements. The listed primary outcome is mean serum 25-hydroxyvitamin D concentration in schoolchildren, measured by liquid chromatography-tandem mass spectrometry at day 0 and day 49.
Numerical primary-outcome results and analysis results are not reported in the registry record. The safety listing records zero serious adverse events, zero other adverse events, and zero deaths in each of five groups. The record does not explain why the safety listing has five groups while the intervention list has six.