Comparison of a Needle-free Injection Method With a Needle-syringe Injection Method: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of a Needle-free Injection Method With a Needle-syringe Injection Method (NCT00990340), a randomized phase 4 study. The primary outcome is Subject-reported Injection Anxiety Immediately Before Administration.

2. Clinical Question

The question concerns a reported psychological response immediately before dosing, rather than pain during or after the injection. The registry also lists secondary measures concerning pain after administration, ease of preparation, ease of administration, and overall satisfaction. Those measures address related but distinct experiences and do not replace the primary anxiety outcome.

The study used a crossover arrangement: participants received both methods in different periods. The reported primary score averages assessments from Period 1 and Period 2, with like groups combined and then averaged. Thus the comparison is between methods experienced by participants in the study, not simply between two groups that each received only one method throughout. The record does not report further details about how period effects or possible carryover were handled in the analysis.

3. Trial Design

This was a randomized, open-label, Phase 4 crossover study. The registry record lists 52 enrolled subjects and describes a 28-day study comprising two 14-day periods. In one sequence, participants used the needle-free T-jet® method first and then crossed over to the needle-syringe method. In the other sequence, they used the needle-syringe method first and then crossed over to the needle-free method. The registry does not report the method used to generate or conceal the randomization sequence.

The primary outcome was subject-reported injection anxiety immediately before each dose. The record describes three visits: screening and random assignment at the beginning of Period 1, crossover to the other assignment on the first day of Period 2, and an end-of-study visit. The primary score is described as the average of assessments in both periods, with like groups combined and then averaged. The reported outcome summaries include 42 observations for each method.

Ten of the 52 enrolled subjects were described as unevaluable. The listed reasons were four discontinuations, three cases of non-compliant dosing or diary use, and three protocol violations. The discontinuations included two adverse events, one loss to follow-up, and one case of inconsistent participation. The protocol violations included two instances of receiving devices out of randomized sequence and one interruption of injection due to a device; the description of that last event is incomplete in the registry record.

Masking is listed as none. The registry does not report the original sample-size justification, planned statistical model, handling of period or sequence effects, or a detailed analysis plan. It lists no reported statistical analyses. The posted summaries therefore support descriptive comparisons and simple unadjusted calculations, but do not establish what analysis methods were specified in the original protocol.

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.

First 14-day Treatment

Reasons for not completing this period:

Second 14-day Treatment

Analysis population for the primary outcome, as defined in the registry: Of the 52 subjects enrolled, 10 were unevaluable as follows: 4 discontinuations (2 adverse events, 1 lost to follow up, 1 inconsistent participation) 3 non-compliant dosing or diary use, 3 protocol violations ( 2 received devices out of randomized sequence, 1 interruption of injection due to device malfunction.

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 Subject-reported Injection Anxiety Immediately Before Administration, measured over 28 days; Period 1: 14 days, Period 2: 14 days.

The primary endpoint is the mean subject-reported injection-anxiety score immediately before administration of each dose. Participants rated anxiety on a five-point scale, with 1 indicating the most positive response and 5 the most negative response or greater anxiety. The score combines assessments from both 14-day periods over the 28-day study timeframe.

Measuring anxiety immediately before administration focuses on anticipation of the injection. That differs from the secondary pain measure, which is reported immediately following administration. It also differs from the ease and satisfaction measures, which address practical or overall impressions of using the methods. Keeping these outcomes distinct matters because a method could be viewed differently on anticipatory anxiety, pain, preparation, administration, or satisfaction.

A mean provides a concise description of the average recorded score for each method. The standard deviation describes how spread out individual scores were around that mean. The numerical direction is interpretable because the registry gives the anxiety scale anchors: a lower score corresponds to a more positive response and less reported anxiety. The endpoint remains a self-reported scale score, however, and the posted average does not reveal the full distribution of individual responses or whether participants’ experiences changed between periods.

7. Results Posted in the Registry

• TevTropin® by Needle-syringe: mean 1.98 versus 2.15 on control; difference -0.17 (95% CI -0.61 to 0.27), standardized effect d = -0.17; z-test p = 0.446.

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.

Subject-reported Injection Pain Immediately Following Administration.

• 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:
  • TevTropin® by Needle-syringe: mean 0.89 versus 0.96 on control; difference -0.07 (95% CI -0.50 to 0.36), standardized effect d = -0.07; z-test p = 0.749.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between TevTropin® by Needle-syringe and the control. The interval gives the range of effects that remain compatible with the data.

Subject or Caregiver Reported Perception of Ease of Preparation as Recorded Weekly on a 5-point Scale.

• 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:
  • TevTropin® by Needle-syringe: mean 1.78 versus 2.55 on control; difference -0.77 (95% CI -1.24 to -0.30), standardized effect d = -0.70; z-test p = 0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for TevTropin® by Needle-syringe than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Subject or Caregiver Reported Perception of Ease of Administration as Recorded Weekly on a 5-point Scale.

• 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:
  • TevTropin® by Needle-syringe Followed byTevTropin® Needle-free: mean 1.76 versus 2.40 on control; difference -0.64 (95% CI -1.13 to -0.15), standardized effect d = -0.56; z-test p = 0.011.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for TevTropin® by Needle-syringe Followed byTevTropin® Needle-free than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Across the posted secondary outcomes, the numerical contrasts do not all point to the same kind of experience. The post-administration pain comparison is close to zero, while the two ease measures show larger method contrasts in their posted averages. The record also lists overall satisfaction as a secondary outcome, but a result for that outcome is not reported in the registry record.

This pattern is distinct from the primary anxiety comparison, whose estimated mean difference was small and whose confidence interval included zero. Secondary measures may help describe other aspects of using the devices, but they do not change what the primary endpoint measures. In particular, ease of preparation and ease of administration are not interchangeable with anxiety before dosing or pain after dosing. The registry does not report the scale anchors for the ease measures, so the numerical direction alone does not establish which method was perceived as easier.

The posted secondary comparisons are unadjusted. When several outcomes are examined, the chance of finding at least one apparently unusual result can increase unless the analysis accounts for multiplicity. The registry record does not report a multiplicity strategy or adjustment. Consequently, secondary p-values carry less weight as confirmatory evidence than a prespecified primary comparison would, and the results are best treated as descriptive signals that require cautious interpretation.

The secondary registry entries list least-squares means, but no reported analyses are listed. Simple unadjusted recalculations from summary statistics may not reflect any model-based analysis the investigators performed. The record does not explain whether these outcomes were planned for formal hypothesis testing or how their interdependence was handled. Taken together, the secondary pattern broadens the description of participant and caregiver experience but does not provide a single overall ranking of the methods.

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

• Subject-reported Injection Pain Immediately Following Administration.
• Subject or Caregiver Reported Perception of Ease of Preparation as Recorded Weekly on a 5-point Scale.
• Subject or Caregiver Reported Perception of Ease of Administration as Recorded Weekly on a 5-point Scale.
• Subject-reported Overall Satisfaction Following the End of Each Period of the Study.

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: it is recorded as a numerical score and summarized by a mean and standard deviation. The mean is the arithmetic average of the recorded scores. The standard deviation describes their dispersion around that average; a larger standard deviation indicates greater variability among the observed scores. These summaries describe the data but do not, on their own, account for the crossover structure.

What does the mean difference represent?

The posted contrast is needle-syringe minus needle-free. Its estimate is -0.17, formed from the reported method means of 1.98 and 2.15. Since the anxiety scale assigns higher values to more negative responses or greater anxiety, a negative contrast corresponds numerically to a lower average score for the needle-syringe method. This is a direction-of-scale description, not a conclusion that the method has a meaningful advantage. The size and uncertainty of the estimate must be considered together.

How should the confidence interval be read?

A confidence interval gives a range of values reasonably compatible with the observed data under the method’s assumptions. For the primary mean difference, the 95% interval is -0.607 to 0.267. It contains zero, the value corresponding to no average difference under this contrast. It also extends to values on both sides of zero, so the estimate is not precise enough to pin down the direction of the average difference. A confidence interval is not a range containing a fixed proportion of individual participants’ scores, and it is not a probability statement about the true value after the data have been observed.

What does the p-value add?

The unadjusted p-value for the primary comparison is 0.446. A p-value measures how compatible the observed data are with a specified null hypothesis, under the calculation’s assumptions. It is not the probability that the null hypothesis is true, and it does not show whether a difference is important. Its interpretation depends on the analysis being appropriate for the design and outcome. The registry does not report the primary statistical analysis model, so the posted p-value should be understood as the listed unadjusted result rather than evidence about an undocumented model.

Why does crossover structure matter?

In a crossover study, the same participant receives both methods, so their two experiences may be related. A paired analysis can use within-participant comparisons and account for that dependence. Period and sequence may also matter: participants receive one method in the first period and the other method in the second, and an experience in one period could affect responses in another. The record gives the crossover sequences and the averaging approach but does not report how the primary analysis handled within-person correlation, period effects, sequence effects, or carryover. A calculation that treats the method summaries as if they were independent groups may not reproduce a paired crossover analysis.

What are recalculated comparisons?

Recalculated comparisons are simple unadjusted calculations from the posted summary statistics. They can make the numerical contrast and its uncertainty easier to interpret, but they are not necessarily the trial’s own analysis. For the primary comparison, the registry reports no discrepancy between the posted result and the recalculation. For some secondary outcomes, the available summary-based standard deviations are approximate. The registry lists no reported analyses for the secondary outcomes, so those recalculations do not establish the methods used in the original study.

What can be inferred from the reported summaries?

The available summaries support a description of the observed average scores and a cautious assessment of their uncertainty. They do not reveal participant-level response patterns, missing-data assumptions, or the impact of within-subject correlations. The record also does not report whether a particular model was prespecified or whether results were adjusted for examining multiple outcomes. Those omissions limit how far the reported comparisons can be generalized beyond their descriptive role. Statistical interpretation should distinguish what the numeric estimates show from what the registry does not document.

11. Confidence Intervals and Precision

The primary mean difference is -0.17, with a 95% confidence interval from -0.607 to 0.267. The interval crosses zero, so the posted data do not determine whether the average anxiety score was lower with the needle-syringe method or with the needle-free method. The point estimate is on the needle-syringe-lower side of zero, but values on the other side also remain compatible with the interval.

The interval’s breadth is important: the observed estimate is not precise enough to isolate a narrow range of possible mean differences. It includes a value close to no difference as well as values farther from zero in both directions. The interval concerns the mean contrast, not the range of individual scores. Individual variation is also reflected in the reported standard deviations of 1.019 for the needle-free method and 1.024 for the needle-syringe method.

The unadjusted p-value is 0.446. This is consistent with the confidence interval including zero, but neither statistic proves the absence of a difference. The registry does not report a threshold for a clinically or practically important change on this anxiety scale, so the interval cannot be classified against such a threshold using the record alone.

Precision is also affected by the study’s analysis population and design. The record reports 42 observations for each method and states that 10 enrolled subjects were unevaluable. It does not report a detailed missing-data analysis or the model used to account for paired observations and period effects. The confidence interval should therefore be interpreted as the posted uncertainty estimate, with those reporting gaps in mind.

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 events. They are illustrative calculations based on the observed effect and assume 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. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the estimated participants per arm for a hypothetical study to have an 80% chance of detecting the specified effect under those planning assumptions, if that effect were the true one. The 90% power column gives the corresponding number for a 90% chance. These are design-planning quantities, not probabilities that the observed trial result is correct. This is not observed power.

Rows planning for 100%, 75%, or 50% of the observed effect represent progressively smaller target effects. Smaller effects are harder to distinguish from random variation, so they require more participants per arm to achieve the same planned power. The figures are illustrations tied to the observed effect and the stated assumptions; they should not be read as the sample size the investigators actually selected or as proof that a future study will achieve its target.

The crossover design is another reason to treat these figures as planning illustrations rather than a reconstruction of the original study design. The listed assumptions describe a two-arm equal-allocation calculation, while the trial assigned sequences and had each participant use both methods. The registry record does not report the original design calculation or the assumptions used for it.

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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.170; pooled standard deviation σ = 1.022.
2. n = 2 × (1.96 + 0.842)² × 1.022² / -0.170² = 566.8, rounded up to 567 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
delta <- -0.17                      # observed difference in means
sigma <- 1.02150305922205                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(990340)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 567 (80% power), 759 (90% power)
 75% of observed effect: n per arm = 1,008 (80% power), 1,349 (90% power)
 50% of observed effect: n per arm = 2,268 (80% power), 3,036 (90% power)
power.t.test: 567.7 
Simulated power at n = 567 per arm: 0.801 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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 one primary anxiety outcome and several secondary outcomes, including pain after administration, ease of preparation, ease of administration, and overall satisfaction. It does not report a plan for controlling multiplicity across outcomes, a hierarchy of secondary hypotheses, or whether any secondary tests were intended to be confirmatory. When multiple outcomes are examined, unadjusted p-values do not account for the increased opportunity to observe a small p-value by chance. The posted secondary p-values should therefore be interpreted cautiously rather than as a set of independent confirmations.

The record reports 52 enrolled subjects and identifies 10 as unevaluable for the primary endpoint. The stated reasons include discontinuations, non-compliant dosing or diary use, and protocol violations. Although the outcome summaries report 42 observations for each method, the registry does not describe an intention-to-treat analysis, a per-protocol analysis, imputation, or sensitivity analyses for missing data. It also does not give a fuller account of which observations were omitted from each endpoint or how missing assessments were handled.

The crossover design raises additional analysis questions. The registry describes randomized sequence assignment and a switch of methods after the first 14-day period, but does not report whether the analysis accounted for pairing within participants, period effects, sequence effects, or possible carryover. The record does not report the statistical model or detailed analysis plan. These are not details that can be inferred from method-specific averages alone.

The registry lists no reported statistical analyses. As a result, it is not possible to determine from the record whether the posted comparisons were the prespecified primary analysis, whether exclusions were defined in advance, or whether analyses beyond those posted were conducted. These gaps do not invalidate the descriptive statistics, but they limit confidence in interpreting the comparisons as a complete account of the planned inferential analysis.

15. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The registry reports zero participants with serious adverse events in each sequence group, with 42 participants at risk in each group. It also reports zero participants affected by other adverse events in each group, with 42 at risk. These figures describe the posted counts for the two sequence groups over the study; they should not be read as evidence that no adverse events of any kind occurred among all enrolled subjects.

The record does not list serious adverse event terms. Death counts are not reported in the registry record. The listed reasons for discontinuation include two adverse events, but the registry does not give further details in the endpoint description. Accordingly, the zero affected counts in the posted adverse-event groups should be read alongside the limited event detail and the separate discontinuation information, rather than as a complete account of individual event narratives.

These are descriptive safety counts from a study with 42 participants at risk in each sequence group. They do not quantify rare risks or establish comparative safety. The record does not provide a more detailed safety analysis or further information about event severity, timing, or relationship to the injection method.

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

The primary result describes average anxiety ratings immediately before Tev-Tropin® administration during a short crossover comparison. The posted mean was 2.15 with the needle-free method and 1.98 with the needle-syringe method. The estimated contrast was -0.17 for needle-syringe minus needle-free, on a scale where lower scores indicate a more positive response and less reported anxiety. The uncertainty interval includes zero, so the data do not establish a clear difference in mean anxiety between the methods.

This does not mean the methods are equivalent. Equivalence requires a defined margin and an analysis designed to show that differences lie within that margin; neither is reported in the registry record. Nor does the result prove that there is no difference. The confidence interval remains compatible with values on either side of zero, and the registry does not specify what size of score change would be meaningful to participants.

The finding is limited to the measured outcome and study setting. Anxiety immediately before administration is not the same as pain following administration, ease of preparation, ease of administration, or overall satisfaction. The secondary results offer additional descriptive information, but the registry does not report a multiplicity plan or a complete analysis strategy for them. Scale anchors for ease outcomes are not reported, which also constrains interpretation of their numerical direction.

The crossover design allowed participants to experience both methods, but the record does not report how the inferential analysis addressed the paired observations or period and sequence effects. Ten enrolled subjects were unevaluable for the primary outcome. Without a reported missing-data strategy, detailed participant-level data, and the original statistical plan, the posted summaries cannot resolve every design and analysis question.

Accordingly, the result is best understood as a modest observed difference with substantial uncertainty, rather than a verdict that one method is better or that the methods produce identical experiences. It concerns reported scores among the participants represented in the posted summaries, not a guarantee about any individual’s experience.

17. Why This Trial Matters Statistically

This study illustrates why the design and the outcome need to be read together. The primary measure is an anticipatory, subject-reported anxiety score, while other measures address pain after dosing, ease, and satisfaction. Those outcomes capture different aspects of experience, so one numerical contrast cannot stand in for all of them. The scale’s direction is particularly important: lower primary scores mean a more positive response and less anxiety.

The crossover structure is also statistically consequential. Participants used both methods, making within-participant dependence relevant to analysis. Yet the registry record does not report whether the primary comparison accounted for pairing, period, sequence, or carryover. Method-specific means and a simple difference are informative descriptions, but they cannot show how these design features were handled in the original analysis.

The primary confidence interval includes zero, illustrating the distinction between an observed direction and a well-determined effect. The point estimate lies on one side of zero, but the interval allows values on both sides. That uncertainty is more informative than treating a single estimate or p-value as a complete conclusion. It also reinforces that failure to establish a difference is not the same as demonstrating equivalence.

Finally, the record’s reporting gaps matter for interpretation. Ten enrolled subjects were unevaluable, the original sample-size rationale is not reported, and the registry lists no reported analyses. Secondary outcomes were also posted without a reported multiplicity strategy. These limitations show why transparent reporting of analysis populations, model choices, and planned outcome handling is essential for evaluating a trial, even when summary statistics are available.

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.

Several trial-specific limitations constrain interpretation. The study was open-label, and the primary endpoint was self-reported immediately before dosing. The registry does not report whether participants or caregivers received standardized instructions beyond the scale description, or whether expectations about the devices were assessed. The record therefore cannot separate the recorded responses from possible effects of knowing which method was being used.

The design was a crossover, but the registry does not report how the analysis handled within-participant correlation, period effects, sequence effects, or possible carryover between the two 14-day periods. It describes the method sequence and averaging approach, but not a complete statistical model. This prevents a full assessment of whether the posted comparison reflects the structure of the data.

Ten of the 52 enrolled subjects were unevaluable for the primary outcome, with several reasons reported. The record does not describe how missing observations were handled, whether the analysis population was defined in advance, or whether sensitivity analyses were performed. It also does not state the original sample-size justification or the minimum difference considered meaningful on the anxiety scale.

Other limitations include the absence of a reported multiplicity plan for the secondary outcomes and the lack of listed statistical analyses. The ease scales’ anchors are not reported, and the satisfaction result is not reported in the registry record. The registry description of one protocol violation is incomplete. These reporting gaps do not alter the posted numbers, but they limit assessment of their context and robustness.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Comparison of a Needle-free Injection Method With a Needle-syringe Injection Method — NCT00990340.
• Registry record last updated 2011-07-25; status last verified 2011-06.
• Results first posted 2011-07-25.
• 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 record describes a randomized, open-label, Phase 4 crossover study of Tev-Tropin® delivered by needle-free T-jet® and needle-syringe methods in pediatric subjects with human growth hormone deficiency. The study enrolled 52 subjects and used two 14-day periods. The primary outcome was subject-reported anxiety immediately before administration on a five-point scale, with lower scores indicating a more positive response and less anxiety.

Ten subjects were unevaluable for the primary outcome, and the posted method summaries each include 42 observations. The primary mean difference was -0.17 for needle-syringe minus needle-free, with a 95% confidence interval from -0.607 to 0.267 and an unadjusted p-value of 0.446. The interval includes zero. The registry does not report the original sample-size justification, detailed statistical analysis plan, or reported statistical analyses.