Home Based Peer Support Program for Mothers With Low Breastfeeding Self-efficacy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Home Based Peer Support Program for Mothers With Low Breastfeeding Self-efficacy (NCT04621266), a randomized na study. The primary outcome is Infant Feeding Status: Exclusive Breastfeeding.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group trial with single masking. The registry record lists an enrollment of 442 and identifies The University of Hong Kong as the sponsor. The intervention was online home-based peer support added to standard usual care; the comparison group received standard usual care. The record marks the study as completed.

The primary outcome was recorded for 224 participants in the intervention arm and 218 in the usual-care arm. The outcome was measured at 1 month postpartum. The posted primary results count 46 participants with exclusive breastfeeding in the intervention arm and 39 in the usual-care arm. These are outcome counts, not descriptions of the full range of participant characteristics or follow-up completeness.

The trial record lists breastfeeding self-efficacy and postpartum depression assessments among the secondary outcomes. Self-efficacy assessments are identified at baseline, 2 months, and 4 months postpartum; postpartum depression assessments are listed at baseline, 1 month, and 2 months postpartum. Some listed outcomes do not have results reported in the registry record.

The original sample-size justification, intended analysis population, detailed allocation procedures, and full masking procedures are not reported in the registry record. The record also does not report the detailed intervention protocol or the specific contents of usual care. These omissions limit what can be inferred about trial conduct and the analysis strategy from the registry entry alone.

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

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 Infant Feeding Status: Exclusive Breastfeeding, measured over At 1 month postpartum.

The primary endpoint is infant feeding status classified as exclusive breastfeeding at 1 month postpartum. It is recorded as the number of participants meeting that status, and the endpoint description refers to the number or proportion of participants practicing exclusive breastfeeding. In the posted results, 46 participants in the intervention arm and 39 in the standard usual care arm were counted as exclusively breastfeeding.

This is a binary outcome at the participant level: a participant is counted as having or not having the defined status at the specified assessment time. In general, binary endpoints can be summarized as counts and proportions, and the difference between groups can be expressed on an absolute scale or as a relative measure. Those measures answer different questions: an absolute comparison describes the difference in event frequency, whereas a relative comparison describes the event frequency in one group in relation to the other.

Exclusive breastfeeding is used as a direct measure of the feeding practice named in the trial question. The one-month assessment gives the endpoint a specific time point; it does not by itself describe feeding practices at later times. The registry does not report the operational criteria used to classify exclusive breastfeeding, the method of outcome ascertainment, or how participants with unobserved feeding status were handled.

7. Results Posted in the Registry

• Online Home-based Peer Support Intervention: 20.5% (46/224) versus 17.9% (39/218) on control; risk difference 2.6 percentage points (95% CI -4.7 to 10.0), risk ratio 1.15 (0.78–1.68); unadjusted two-proportion z-test p = 0.480.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Women's Self-efficacy in Breastfeeding

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Online Home-based Peer Support Intervention: mean 45.00 versus 40.70 on control; difference 4.30 (95% CI 2.03 to 6.57), standardized effect d = 0.35; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Online Home-based Peer Support Intervention than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Women's Self-efficacy in Breastfeeding at Baseline

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Online Home-based Peer Support Intervention: mean 37.00 versus 37.00 on control; difference 0.00 (95% CI -1.23 to 1.23), standardized effect d = 0.00; z-test p = 1.000.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Online Home-based Peer Support Intervention and the control. The interval gives the range of effects that remain compatible with the data.

Women's Self-efficacy in Breastfeeding at 2 Months Postpartum

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Online Home-based Peer Support Intervention: mean 40.60 versus 38.70 on control; difference 1.90 (95% CI 0.05 to 3.75), standardized effect d = 0.19; z-test p = 0.044.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Online Home-based Peer Support Intervention than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The listed secondary outcomes cover breastfeeding self-efficacy and postpartum depression at several postpartum assessments. The posted self-efficacy comparisons include baseline and later assessments, with the pattern of group means favoring the intervention arm at the post-baseline assessments. The baseline comparison is consistent with similar mean scores between groups. These outcomes address a different aspect of breastfeeding experience than the primary endpoint, which records exclusive breastfeeding at 1 month postpartum.

The registry lists postpartum depression assessments, but results for those assessments are not reported in the registry record. It also identifies additional self-efficacy time points for which detailed comparisons are not included among the posted results. Consequently, the secondary record does not provide a complete basis for evaluating all listed outcomes or their trajectories.

Secondary results can add context, but they do not erase uncertainty in the primary comparison. They also need cautious interpretation because several outcomes and time points create multiple opportunities to observe a nominally notable result by chance. The registry does not report a multiplicity adjustment or a prespecified hierarchy for secondary outcomes. The posted secondary p-values are unadjusted, so they carry less weight than a clearly prespecified, multiplicity-aware analysis would. Differences in measurement, timing, and completeness also mean that a secondary score should not be treated as a direct confirmation of the primary feeding-status result.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Women's Self-efficacy in Breastfeeding
• Women's Self-efficacy in Breastfeeding at Baseline
• Women's Self-efficacy in Breastfeeding at 2 Months Postpartum
• Women's Self-efficacy in Breastfeeding at 4 Months Postpartum
• Women's Postpartum Depression at Baseline
• Women's Postpartum Depression at 1 Month Postpartum
• Women's Postpartum Depression at 2 Month Postpartum

9. Statistical Interpretation

10. Statistical Methods Explained

The primary endpoint is binary because it records whether each participant met the exclusive-breastfeeding classification at a particular time point. The registry reports the number of participants with the event in each group, along with the group sizes. A count is easier to interpret when considered alongside its group size: the count alone does not show how common the event was in that group. The posted comparison therefore also includes a risk difference and relative measures.

What does the risk difference describe?

In general, a risk difference is the event proportion in one group minus the event proportion in the comparison group. It uses the original probability scale, with zero representing no difference. A positive value means the event proportion is higher in the group named first; a negative value means it is lower. Here the posted estimate is 0.026. Its confidence interval runs from -0.047 to 0.100, so values on either side of zero remain compatible with the interval.

How do relative measures differ?

A risk ratio compares the event proportions by division, while an odds ratio compares event odds. These measures are relative rather than absolute, and can give a different impression of the size of a difference than a risk difference. In this trial, the posted risk ratio is 1.148 and the posted odds ratio is 1.186. Their respective intervals include the no-difference value for each measure. A relative measure should be read on its own scale and together with the event counts and the absolute comparison.

What does a confidence interval convey?

In general, a confidence interval describes the uncertainty around an estimated quantity under the assumptions of the method used to construct it. A narrow interval indicates greater precision than a broad one, while an interval spanning values with different interpretations indicates uncertainty about the direction or magnitude. The primary interval includes zero. The confidence level and the method used to construct the interval are not reported in the registry record, so they should not be inferred from the interval alone.

What does the p-value add?

The reported unadjusted p-value for the primary comparison is 0.48. In general, a p-value measures how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions are correct. It is not the probability that the null hypothesis is true, nor a measure of the size or importance of a difference. The registry does not report the full statistical procedure used to obtain this p-value. The word unadjusted indicates that the posted value is not presented as adjusted for multiple comparisons.

Why does the analysis plan matter?

A prespecified plan can clarify how outcomes, missing observations, repeated assessments, and multiple comparisons are handled. The registry record does not report the original statistical analysis plan, the planned analysis population, or how missing data were treated. It lists zero reported analyses in the analysis field. These absences mean that the posted summaries can be described, but the record does not establish whether they follow a prespecified model or whether other planned analyses were conducted.

What can be said about over-dispersion?

Over-dispersion is a general concern for some count-data models when observed variability exceeds what the model assumes. It can affect standard errors and consequently the precision of model-based estimates. The primary endpoint is posted as a participant count for a binary outcome, with a risk difference and relative measures; no count-model specification or dispersion estimate is reported. Over-dispersion should therefore not be assumed to be part of the trial's analysis, and the record does not provide enough information to evaluate it as a model issue.

Randomization is intended in general to support a fair comparison by assigning participants to groups through a chance process. The registry identifies the allocation as randomized, but does not report allocation-concealment procedures, the sequence-generation method, or the masking details beyond single masking. The registry summaries should not be treated as evidence about those unreported implementation details.

11. Confidence Intervals and Precision

The posted primary risk difference is 0.026, with a confidence interval from -0.047 to 0.100. The interval crosses zero, the value representing no absolute difference. It therefore does not isolate the direction of the difference. Its endpoints also show that a range of effect sizes remains compatible with the reported estimate under the interval method's assumptions.

Precision concerns how tightly an estimate is determined, rather than whether an effect is important. A confidence interval is more informative than a point estimate alone because it displays uncertainty around that estimate. Here, the span from -0.047 to 0.100 allows both a negative and a positive risk difference. The result is not precise enough to rule out either direction based on this interval.

The relative comparisons have the same general limitation. The risk ratio is 1.148, with an interval from 0.782 to 1.685; the odds ratio is 1.186, with an interval from 0.738 to 1.906. Each interval includes its scale's no-difference value. These measures do not remove the uncertainty in the primary result, and they should not be interpreted as more conclusive simply because they are expressed relatively.

The confidence level and interval-construction method are not reported in the registry record. Precision judgments should therefore stay with the posted interval endpoints and avoid assuming an unreported confidence level or statistical procedure. The group counts and interval together describe the evidence available for this endpoint and time point, not the precision of every secondary outcome or of any later breastfeeding measure.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total participants and not total events. They are illustrations computed from the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Each row considers detecting a stated fraction of the observed effect. For the primary endpoint, the illustration gives 3,480 participants per arm for 80% power and 4,658 participants per arm for 90% power when planning for 100% of the observed effect. Planning for 75% of the observed effect gives 6,105 and 8,173 participants per arm; planning for 50% gives 13,553 and 18,142 participants per arm.

In general, 80% power means that, if the effect used for planning were the true effect and the assumptions held, the design would have an 80% chance of detecting it at the stated significance level. The 90% column describes the corresponding chance at 90% power. These are design concepts, not probabilities that the trial's result is correct. This is not observed power.

Smaller effects are harder to distinguish from random variation, so the planning illustrations require more participants per arm as the assumed effect becomes smaller. The reported assumptions describe these illustrations only. The trial's original sample-size assumptions and justification are not reported in the registry record. The figures should not be read as the number actually enrolled or as evidence that the trial was planned using this calculation.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.179; treatment proportion p₁ = 0.205; average p̄ = 0.192.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5572 = 1.0920.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5568 = 0.4687.
4. n = (1.0920 + 0.4687)² / (0.0265)² = 3,479.4, rounded up to 3,480 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.178899082568807                          # control proportion
p1 <- 0.205357142857143                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(4621266)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 3,480 (80% power), 4,658 (90% power)
 75% of observed effect: n per arm = 6,105 (80% power), 8,173 (90% power)
 50% of observed effect: n per arm = 13,553 (80% power), 18,142 (90% power)
power.prop.test: 3479.4 
Simulated power at n = 3,480 per arm: 0.804 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and multiple secondary outcomes, including repeated assessments of breastfeeding self-efficacy and postpartum depression. When many outcomes or time points are examined, the chance of at least one apparently notable result can increase. In general, multiplicity procedures address that issue by adjusting the interpretation or testing threshold across a defined family of comparisons. Whether such a procedure was planned or used is not reported in the registry record.

The record does not report a statistical analysis plan, a hierarchy among secondary outcomes, or a multiplicity adjustment. It lists zero reported analyses in the analysis field, and the detailed secondary records do not include reported analyses. The available unadjusted comparisons can be described as posted, but the registry does not explain whether they were prespecified or selected from a larger set of analyses. This uncertainty makes isolated secondary findings less persuasive than results supported by a documented analysis strategy.

Missing-data handling is also not reported in the registry record. The registry gives outcome denominators for the primary comparison and for some secondary measures, but it does not explain why those denominators differ from the overall enrollment, whether assessments were missing, or how any missing values were handled. The number of participants with an outcome cannot by itself identify the reasons for differences in available data.

The intended analysis population is not reported in the registry record. It is therefore not possible to determine from the record whether the analysis followed an intention-to-treat principle, used a per-protocol population, or applied another definition. The registry also does not describe adjustments for baseline variables, methods for repeated measurements, or sensitivity analyses. These are reporting gaps, not evidence that any particular method was or was not used in the full trial.

15. 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 reports zero serious adverse events among 224 participants at risk in the online home-based peer support arm and zero among 218 participants at risk in the standard usual care arm. It also reports zero other adverse events among 224 and 218 participants at risk, respectively, and zero deaths in each group. No serious adverse-event terms are listed.

These figures describe what was recorded in the registry for the stated groups. They do not establish that no adverse experiences occurred outside the categories or reporting procedures captured in the record. The registry does not report further details about adverse-event definitions, collection methods, follow-up duration for safety, or attribution to the intervention. Zero reported events should therefore be read as a feature of the posted safety record, not as proof that an intervention has no risk.

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

The primary result describes exclusive breastfeeding status at 1 month postpartum in the two randomized groups. The posted estimate is a risk difference of 0.026, and its interval from -0.047 to 0.100 includes zero. The unadjusted p-value is 0.48. Together, these results do not establish a clear difference on this endpoint, and the interval leaves uncertainty about both direction and magnitude.

This finding does not show that the groups are equivalent. Demonstrating equivalence or non-inferiority requires an appropriate design, a prespecified margin, and analysis methods; such information is not reported in the registry record. Nor does a result that does not establish a difference mean that the intervention had no effect. The estimate remains uncertain, and a range of differences is compatible with the interval.

The endpoint concerns one postpartum assessment. It does not answer whether exclusive breastfeeding continued for longer, whether feeding patterns changed at later times, or whether other outcomes differed. The trial's listed secondary measures include self-efficacy and postpartum depression, but not all of their results are reported in the registry record. The primary result should not be generalized to those separate outcomes.

The registry entry also does not provide enough information to assess the full analysis plan, missing-data procedures, outcome classification details, or the representativeness of the enrolled participants. Interpretation should therefore remain bounded by the reported groups, outcome, and time point. The record supports describing the observed comparison and its uncertainty, not making medical recommendations or broad claims about effectiveness.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate alone is not enough to interpret a randomized comparison. The primary risk difference is positive, but the interval includes zero and extends to values on either side. The accompanying uncertainty changes how the result should be read: the posted data do not pin down a clear direction or a precise magnitude for the group difference.

It also shows the value of distinguishing absolute and relative measures. A risk difference, risk ratio, and odds ratio summarize the same binary endpoint on different scales. Reporting them alongside event counts helps readers see that no single measure removes the underlying uncertainty. Statistical interpretation should attend to the scale, interval, and endpoint definition rather than relying on one headline statistic.

The record lists outcomes at multiple times and across more than one domain. That makes clear reporting of prespecification, missing-data handling, analysis populations, and multiplicity important. Those details are not reported in the registry record, limiting the ability to judge how the posted secondary findings fit into a planned analysis.

Finally, the planning illustrations make the relationship between effect size and required sample size visible: smaller assumed effects call for larger participant counts. These calculations are separate from the original trial design, whose assumptions are not reported. Keeping planning illustrations distinct from observed results prevents a common statistical confusion between design power and evidence in the completed trial.

18. 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 registry record gives a concise description of the trial but omits details needed to assess several design and analysis issues. Eligibility criteria, participant characteristics, allocation sequence generation, allocation concealment, and detailed masking procedures are not reported in the registry record. The description of the online peer support program and the components of standard usual care is also limited.

The record does not report how exclusive breastfeeding was defined and ascertained, how missing outcome data were handled, or why the available outcome denominators differ across results. The analysis population, statistical analysis plan, and any adjusted analyses are not reported. Without these details, it is not possible to determine how robust the posted comparisons are to alternative assumptions or analytic choices.

The primary endpoint is measured at 1 month postpartum, so it does not by itself describe breastfeeding duration or outcomes at later times. Although the registry lists additional breastfeeding self-efficacy and postpartum depression assessments, results for all listed assessments are not reported. The absence of those results limits interpretation of the full set of planned or registered outcomes.

The safety record reports no serious or other adverse events and no deaths, but detailed definitions and collection procedures are not reported. The registry also does not provide information about adherence to the intervention or the extent of peer support received. These limitations apply to what can be concluded from the registry entry; they do not establish whether the full trial report contains additional information.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Home Based Peer Support Program for Mothers With Low Breastfeeding Self-efficacy — NCT04621266.
• Registry record last updated 2026-02-17; status last verified 2023-08.
• Results first posted 2025-01-20.
• 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.

22. Record Summary

The registry describes a completed randomized, parallel-group, single-masked trial sponsored by The University of Hong Kong, with enrollment of 442. It compared online home-based peer support added to standard usual care with standard usual care alone among Chinese mothers with low breastfeeding self-efficacy.

The primary outcome was exclusive breastfeeding at 1 month postpartum. The posted risk difference was 0.026, with a confidence interval from -0.047 to 0.100 and an unadjusted p-value of 0.48. The interval includes zero, leaving uncertainty about the direction and size of the group difference. Secondary outcomes included breastfeeding self-efficacy and postpartum depression, but results are not reported for all listed assessments. Details of the trial's original sample-size justification, analysis plan, missing-data handling, and analysis population are not reported in the registry record.