txt2protect: Using Text Messaging to Increase HPV Vaccination Among Young Sexual Minority Men: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for txt2protect: Using Text Messaging to Increase HPV Vaccination Among Young Sexual Minority Men (NCT02994108), a randomized na study. The primary outcome is Retention.

2. Clinical Question

This is a feasibility-oriented question, not simply a test of whether the two groups differ on a clinical outcome. Retention indicates whether participants remained engaged through the scheduled assessment, an important practical feature of a longer intervention study. The posted primary outcome counts are 63 participants in txt2protect and 69 in Sexual Health Control, with outcome denominators of 72 and 76, respectively. The registry defines retention as completion of the 9-month assessment among randomized participants, although the explanation of participant withdrawals means that outcome handling also matters when interpreting the counts.

The study’s broader stated aim was to assess feasibility, acceptability, and preliminary efficacy. The registry lists HPV-related knowledge and several motivation and behavioral-skills measures as secondary outcomes. Those measures describe self-reported or assessed constructs; they are not the same as a reported vaccination endpoint. Whether vaccination behavior itself was measured as an outcome is not reported in the registry record.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study, marked as completed, with 150 participants randomized. Its listed interventions were txt2protect and Sexual Health Control, both classified as behavioral interventions. The phase is listed as not applicable. The specific role of the masking and the method used to implement randomization are not reported in the registry record.

The txt2protect description says content was delivered in two phases over 36 weeks. In Phase 1, weeks 1-3, participants received 10-12 messages daily; in Phase 2, weeks 4-36, messages were monthly. Phase 1 content was organized into three modules. The registry’s description of the control condition also gives two phases over 36 weeks, the same message-frequency schedule, and three Phase 1 modules, but says the content was topic-based. The full content descriptions are not reported in the registry record.

The primary outcome was retention at the 9-month assessment. The registry states that three participants in txt2protect withdrew. One of them gave permission for data through withdrawal in month 3 to be used and was included in the reported population description, which is truncated in the registry record. The outcome counts are reported for 72 txt2protect participants and 76 control participants. How those denominators relate to every randomized participant, and the analysis population used for each outcome, are not reported in the registry record.

The registry also reports secondary outcomes assessed at 3 weeks, including HPV-related knowledge, attitudes, and subjective norms. It lists additional secondary outcomes, but details for all measures and their analyses are not reported in the registry record. The original sample-size rationale, planned statistical analysis, and any planned interim analyses are 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: Although 155 participants completed the baseline survey, only 150 of them were randomized. A double screening protocol was used to ensure participants who had already been vaccinated were not accidentally enrolled. Five participants reported receiving a dose of HPV vaccine on baseline so they were no longer eligible for the RCT.

Intervention Messages

Reasons for not completing this period:

Phase 1 Assessment

Reasons for not completing this period:

Phase 2 Assessment

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: A total of 150 participants were randomized. Three participants, all of whom were in the txt2protect arm, withdrew from the study. One of the three participants who withdrew provided permission to use include his data up until his withdrawal in month 3 and thus this participant was included in the primary analysis.

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 Retention, measured over 9 Month.

The primary endpoint is retention, measured as the number of participants who completed the 9-month assessment. The registry defines the retention rate as the number completing that assessment divided by the number randomized to either study condition. It states that an 80% retention rate at 9 months would indicate a feasible intervention.

Retention is used in a pilot study because successful follow-up is necessary to collect later outcome information and to judge whether trial procedures can be carried out. It is distinct from an outcome such as vaccination: a participant can complete an assessment without changing vaccination behavior, and completion alone does not establish acceptability or efficacy. The registry identifies feasibility, acceptability, and preliminary efficacy as study aims, but the primary endpoint addresses retention.

The posted outcome counts are 63 of 72 in txt2protect and 69 of 76 in Sexual Health Control. These are counts of participants, not a direct measure of vaccine uptake. The comparison estimate is a risk difference, with a confidence interval that includes zero. The counts and comparison therefore describe the observed follow-up experience in this pilot, while the interval conveys uncertainty about the difference between conditions. How missing assessments were handled in the sponsor’s analysis is not reported in the registry record.

Withdrawal details are relevant to interpretation. Three txt2protect participants withdrew, and one allowed data collected through month 3 to be retained. The registry record does not provide equivalent withdrawal details for the control condition, nor does it fully explain the relationship between withdrawals, the outcome denominators, and the analysis population. Those omissions limit how completely the endpoint can be reconstructed from the record.

7. Results Posted in the Registry

• txt2protect: 87.5% (63/72) versus 90.8% (69/76) on control; risk difference -3.3 percentage points (95% CI -13.3 to 6.7), risk ratio 0.96 (0.86–1.08); unadjusted two-proportion z-test p = 0.519.

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.

Information: HPV-related Knowledge

• 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:
  • txt2protect: mean 1.11 versus 1.00 on control; difference 0.11 (95% CI -0.04 to 0.26), standardized effect d = 0.24; z-test p = 0.149.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between txt2protect and the control. The interval gives the range of effects that remain compatible with the data.

Motivation: Attitudes

• 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:
  • txt2protect: mean 4.51 versus 4.11 on control; difference 0.40 (95% CI 0.15 to 0.65), standardized effect d = 0.53; z-test p = 0.002.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for txt2protect than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Motivation: Subjective Norms

• 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:
  • txt2protect: mean 4.10 versus 4.11 on control; difference -0.01 (95% CI -0.30 to 0.28), standardized effect d = -0.01; z-test p = 0.945.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between txt2protect and the control. The interval gives the range of effects that remain compatible with the data.

The secondary results cover short-term measures of HPV-related knowledge, attitudes, subjective norms, and other listed constructs. Nine secondary outcomes are posted, while the registry lists a broader set of measures and analyses. The detailed results indicate a mixed pattern rather than a consistent shift across all psychological or behavioral-skill measures. That pattern is not the same as evidence about the primary retention endpoint, and it does not establish a change in HPV vaccination behavior.

The secondary measures were assessed at 3 weeks, whereas the primary endpoint concerns completion of the 9-month assessment. They therefore address different questions and time points. Retention reflects whether participants completed follow-up; score comparisons reflect measured constructs. A difference in one type of outcome does not imply a difference in the other.

Unadjusted secondary results carry less weight because multiple outcomes create multiple opportunities for apparently notable findings. If many tests are conducted, some may produce small p-values by chance even when there is no underlying effect. Whether a multiplicity adjustment or a prespecified hierarchy was used is not reported in the registry record. The registry also does not report whether the detailed secondary analyses were confirmatory or exploratory.

These outcomes can help identify patterns for further study, but interpretation should account for their multiplicity, their short assessment timeframe, and the incomplete statistical-plan information. They are preliminary signals, not a substitute for a clearly specified primary endpoint or a direct report of vaccination outcomes. No conclusion about the full set of secondary endpoints can be drawn from only the detailed measures reported in the record.

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

• Information: HPV-related Knowledge
• Motivation: Attitudes
• Motivation: Subjective Norms
• Motivation: Perceived Susceptibility
• Motivation: Perceived Severity
• Motivation: Anticipated Regret
• Behavioral Skills: Perceived Behavioral Control
• Behavioral Skills: Self-efficacy

9. Statistical Interpretation

10. Statistical Methods Explained

General: Random allocation is intended to make the study groups comparable on average at the start of a trial. The registry labels this study randomized and parallel-group, but the sequence-generation and allocation-concealment procedures are not reported in the registry record. Single masking is recorded, but who was masked is not reported in the registry record. These details matter because they help readers assess how assignment and knowledge of assignment could affect outcomes or their measurement.

How is retention compared?

Retention is a binary outcome at participant level: a person either completed the 9-month assessment or did not. The posted counts give the number retained and the denominator for each group. The recalculated risk difference expresses the difference between the groups’ retention proportions, with txt2protect compared against Sexual Health Control. A negative estimate corresponds to a lower observed proportion in txt2protect. The registry analysis uses a chi-squared test to assess evidence of a group association in the retention counts. The test statistic is 0.415 and the reported p-value is .601.

General: A p-value describes how surprising data at least as inconsistent with a specified null hypothesis would be if that null model and the test assumptions held. It does not give the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. A large p-value does not demonstrate equivalence. For equivalence or non-inferiority conclusions, the trial would need an appropriate prespecified design and analysis; those are not reported in the registry record.

Why show an unadjusted recalculation?

The recalculated comparisons are simple, unadjusted analyses of posted summary statistics. For retention, the recalculated risk difference is accompanied by a confidence interval and an unadjusted p-value. For continuous outcomes, the recalculation uses the posted group means, standard deviations, and sample sizes to express a mean difference and its interval. These calculations provide a transparent comparison based on the reported summaries, but they are not substitutes for the sponsor’s own analysis. They may differ if the sponsor used other model specifications, covariate adjustments, analysis populations, or missing-data procedures. Those details are not reported in the registry record.

The reported analyses for the secondary measures are two-sided t-tests of final values. The registry reports the direction and magnitude of those differences using its own group ordering, along with p-values. A t-test compares group means relative to their variability and the amount of information in each group. It relies on assumptions about the sampling distribution and the suitability of a mean-based comparison. The registry does not report diagnostics or additional model details, so these cannot be assessed from the record.

What do confidence intervals add?

General: A confidence interval describes the range of estimates reasonably compatible with the data and the model used to calculate it. An interval that includes zero for a difference does not rule out a real difference; it indicates that the estimate is not precise enough to exclude zero at the corresponding confidence level. An interval entirely on one side of zero indicates that zero is outside that interval, but does not by itself establish that a result is important, reliable across outcomes, or free from bias. The confidence level used for the posted comparison intervals is not specified in the registry record.

For the primary risk difference, the interval includes zero and also covers differences in either direction. That breadth signals uncertainty about the size and direction of the underlying retention contrast. For the secondary means, the same interpretation applies to intervals for mean differences. These comparisons are unadjusted, and multiple secondary outcomes were assessed. Their p-values therefore should not be treated as if each were the only question asked.

What assumptions are missing?

The original trial sample-size calculation and its assumptions are not reported in the registry record. Neither the planned primary analysis details nor the handling of missing outcomes are reported in enough detail to reconstruct the sponsor’s full analysis. The registry’s posted planning illustrations are separate calculations using observed effects and stated assumptions; they are not evidence that the original trial was designed with those sample sizes. An interim-analysis plan is not reported in the registry record.

General: Over-dispersion occurs when outcome variability exceeds what a chosen statistical model expects. It can make standard errors too small if the model does not account for the extra variability, leading to intervals that are too narrow and p-values that appear more persuasive than warranted. The registry does not report a count-based over-dispersion analysis for the primary endpoint, and over-dispersion is not a central feature of this binary retention comparison. For the continuous secondary outcomes, the posted standard deviations show variability, but no diagnostic assessment is reported.

Overall, the registry presents a simple primary comparison and final-value tests for selected secondary measures. The combination of a pilot setting, incomplete analysis details, and multiple secondary questions means the estimates are best read as descriptive and preliminary. The underlying statistical plan and the original sample-size justification are not reported in the registry record.

11. Confidence Intervals and Precision

The primary comparison is imprecise: the confidence interval for the recalculated risk difference includes zero and extends to values on either side. Thus, the data do not pin down whether retention was higher or lower in txt2protect, or how large a difference might be. The interval should be read alongside the group counts, rather than treating the point estimate as a definitive effect.

General: A confidence interval represents uncertainty about an estimate under the calculation’s assumptions. Wider intervals indicate less precision; narrower intervals indicate more precision. The interval is not a guarantee that the true effect lies within its bounds, and it does not account for every possible source of bias or uncertainty. The confidence level for the posted recalculated intervals is not reported in the registry record.

For the secondary comparisons, the HPV-related knowledge and subjective-norm intervals include zero, whereas the attitude interval lies above zero for the recalculated txt2protect-minus-control contrast. These intervals describe uncertainty in group mean differences at 3 weeks, not uncertainty in retention or vaccination behavior. The posted sponsor tests and recalculated intervals also reflect different analysis summaries; their p-values are close for some outcomes but not identical for all.

Precision is constrained by the size of the pilot and by the number of participants with reported outcome data. The registry does not provide enough information to determine whether missing observations affected precision beyond the reported denominators. It also does not report a confidence interval for the sponsor’s primary analysis. Consequently, the recalculated interval is useful for understanding the raw comparison, while the registry’s own test remains the posted primary analysis.

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 illustrations express sample sizes as participants per arm for each continuous or binary comparison; they do not report total event counts for a time-to-event analysis. The calculation assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is a stated fraction of the observed effect. The original trial’s own design assumptions and sample-size justification are not reported in the registry record.

The 80% power column gives the estimated number of participants per arm under those planning assumptions for a specified chance of detecting the chosen effect if that effect were the true one. The 90% power column gives the corresponding larger per-arm planning target for a higher chance of detection. These are design illustrations, not a report of what the trial actually achieved. They are not observed power.

Rows for planning for 100%, 75%, and 50% of the observed effect illustrate how the assumed effect size changes the required enrollment. A smaller target effect is harder to distinguish from random variation, so the planning calculation requires more participants per arm. This relationship is especially clear for outcomes where the observed difference is small: the implied sample sizes can become very large. Those values should not be read as a recommendation or as a validated design for a future study. They are mechanical illustrations based on the posted estimates and assumptions, and estimates from a pilot can be unstable.

The observed trial enrolled 150 participants, while the planning values answer a different question: what sample size the stated formula would imply under its assumptions. The calculations do not establish that the pilot was adequately powered for its outcomes, and the original design rationale is not reported in the registry record.

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 = 0.908; treatment proportion p₁ = 0.875; average p̄ = 0.891.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.4399 = 0.8622.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4393 = 0.3697.
4. n = (0.8622 + 0.3697)² / (-0.0329)² = 1,402.7, rounded up to 1,403 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 <- 0.907894736842105                          # control proportion
p1 <- 0.875                          # 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(2994108)
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 = 1,403 (80% power), 1,878 (90% power)
 75% of observed effect: n per arm = 2,412 (80% power), 3,228 (90% power)
 50% of observed effect: n per arm = 5,237 (80% power), 7,010 (90% power)
power.prop.test: 1402.7 
Simulated power at n = 1,403 per arm: 0.802 (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. Analyses Reported by the Sponsor

The registry reports a chi-squared analysis for the primary retention comparison, with test statistic 0.415 and p = .601. The simple unadjusted recalculation from the posted counts gives p = 0.519 and a risk-difference interval that includes zero. The discrepancy flag is false. The recalculation is a transparent analysis of the posted summary counts; the sponsor’s reported test is the trial’s own analysis and should be read as such. The registry does not provide enough detail to identify every reason the p-values differ.

For the secondary measures described in detail, sponsor-reported analyses use two-sided t-tests of final values. Their p-values are .174 for HPV-related knowledge, .002 for attitudes, and .964 for subjective norms. The recalculated unadjusted p-values are 0.149, 0.002, and 0.945, respectively. These are broadly similar summaries, but they are not interchangeable: the reported values come from the registry’s stated analysis, while the recalculations use posted summary statistics.

The registry does not report covariate adjustment, missing-data procedures, or all details needed to recreate the sponsor’s analyses. The recalculated results therefore serve as a check on the direction and rough scale of the posted comparisons, not as a replacement for the analysis specified or conducted by the study team. When interpreting a discrepancy, the sponsor’s own analysis takes precedence only when the record identifies a discrepancy; the registry marks this one as false.

15. Multiplicity, Missing Data and Analysis Populations

The registry lists 14 outcome measures and 14 analyses, and nine secondary outcomes are posted. Multiple outcomes and tests raise a multiplicity concern: the more comparisons made, the greater the chance that at least one result appears statistically notable by chance. This is particularly relevant when the secondary outcomes cover several related constructs and are assessed in the same study.

Whether the study used a formal correction for multiple testing, designated a hierarchy of outcomes, or treated the secondary analyses as exploratory is not reported in the registry record. The p-values for the secondary outcomes should therefore be interpreted individually and cautiously, rather than as a single body of confirmatory evidence. The record also does not state whether any outcomes or analyses were added or changed after the study began.

Missing-data handling is also incompletely described. The registry reports three withdrawals, all in txt2protect, and says one participant permitted data through withdrawal in month 3 to be used. The primary outcome denominators are 72 and 76, with retention counts of 63 and 69. A complete accounting of missing assessments, withdrawals in the control group, and the rules used to include participants in each analysis is not reported in the registry record. Nor is a full intention-to-treat or per-protocol definition reported.

These gaps affect both reproducibility and interpretation. Different approaches to missing outcomes can change the analyzed population and the uncertainty around an estimate. The registry does not provide enough detail to determine the extent or direction of any such effect. The original statistical analysis plan, prespecified multiplicity strategy, and interim-analysis plan are not reported in the registry record.

16. 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 and zero deaths in both groups. The serious-event figures are listed among 72 participants at risk in txt2protect and 76 in Sexual Health Control. Other adverse events are also reported as zero in both groups, using those same at-risk counts.

These are counts recorded in the registry, not proof that no adverse event of any kind occurred. The record’s adverse-event entries indicate no events in the listed categories during the reported period. The serious adverse event terms list is empty. The period covered by safety monitoring and the method used to collect or classify events are not reported in the registry record.

Zero observed events also provide limited information about the possibility of uncommon events, particularly in a pilot of this size. The counts describe what was recorded among participants at risk; they do not establish the absence of risk in other populations or settings. These figures are safety reporting data and should not be conflated with retention or the secondary outcome comparisons.

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

The registry documents a pilot randomized comparison of txt2protect with a text-message Sexual Health Control condition. For the primary endpoint, it reports retention counts in both groups and a sponsor-reported chi-squared test. The recalculated risk-difference interval includes zero, and the reported primary p-value is .601. This means the posted data do not provide a precise estimate of the retention contrast or establish a group difference.

The result does not establish that the groups are equivalent. A non-significant test is not an equivalence test, and the record does not report an equivalence margin or a design intended to demonstrate equivalence. Nor does the primary outcome establish whether either condition changed HPV vaccination behavior: retention measures assessment completion, not vaccination.

The secondary findings concern scores measured at 3 weeks. They are mixed across the detailed measures and should be interpreted cautiously because multiple outcomes were assessed and the registry does not report a multiplicity strategy. These short-term scores cannot be taken as evidence of a sustained change, a change in vaccination, or an effect on HPV infection or related health outcomes.

As a pilot, the study can inform discussion of follow-up and preliminary measurement patterns, but the record leaves important design and analysis details unclear. The original sample-size rationale, full missing-data procedures, and complete analysis plan are not reported in the registry record. The posted results therefore support a limited statistical description of the outcomes recorded, not a definitive claim about efficacy or broad generalizability.

18. Why This Trial Matters Statistically

This trial is statistically informative because its primary endpoint is a feasibility measure rather than a clinical outcome. Retention is central to whether a longer study can collect follow-up data, but it answers a different question from whether an intervention changes vaccination. Keeping those outcomes distinct prevents a retention comparison from being mistaken for evidence of clinical or behavioral effect.

The randomized parallel-group design permits a direct comparison between txt2protect and a behavioral text-message control. At the same time, the pilot’s size and the interval around the recalculated primary contrast make precision a central issue. A point estimate alone can conceal how much uncertainty remains; the interval indicates that the observed comparison does not tightly determine the direction or size of the retention difference.

The record also illustrates why sponsor analyses and simple recalculations should be distinguished. The registry reports its own chi-squared test, while an unadjusted calculation from posted counts yields a different p-value. Seeing both can help readers understand the raw contrast without assuming that a summary-statistic calculation reproduces every detail of the study analysis.

Finally, multiple secondary outcomes make interpretation more complex. A notable result among several measures should not automatically be treated as confirmatory, particularly when multiplicity handling and prespecification are not reported. The study’s statistical value lies in describing the pilot outcomes and identifying what additional design and reporting detail would be needed to interpret them more fully.

19. 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 limitations are specific to the information reported for this trial. First, the registry’s descriptions of both intervention conditions are incomplete. The txt2protect content is truncated, and the full control content is not reported in the registry record. This limits assessment of how the two message programs differed beyond the stated topic-based control content and shared schedule.

Second, the primary outcome is retention, not vaccination. The posted primary results therefore do not answer whether participants received HPV vaccination. Although the study’s stated broader aim includes preliminary efficacy, vaccination outcome data are not reported in the registry record.

Third, the relationship between randomized participants, outcome denominators, withdrawals, and analyzed data is not fully explained. Three txt2protect participants withdrew; one permitted use of data through month 3. Equivalent withdrawal details for the control condition and complete analysis-population definitions are not reported in the registry record. The record also does not fully explain how missing assessments were handled.

Fourth, the original sample-size justification, detailed statistical plan, interim-analysis plan, and multiplicity strategy are not reported in the registry record. These omissions constrain assessment of whether the analyses were prespecified and how to interpret the many secondary outcomes. The identity of the masked party and details of randomization implementation are also not reported in the registry record.

Finally, the study is a pilot involving young men who have sex with men, with the intended setting identified as the Chicago metro area. The registry record does not establish how well these findings generalize beyond the study population or setting. The listed results should therefore be understood within the limits of the reported pilot data and incomplete analysis detail.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: txt2protect: Using Text Messaging to Increase HPV Vaccination Among Young Sexual Minority Men — NCT02994108.
• Registry record last updated 2020-07-20; status last verified 2020-07.
• Results first posted 2020-07-20.
• 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.

23. Record Summary

NCT02994108 is a completed, randomized, single-masked, parallel-group pilot study of txt2protect compared with a Sexual Health Control condition. The registry reports 150 participants randomized. The primary outcome was retention at the 9-month assessment, defined as completion of that assessment among randomized participants. Counts were 63 of 72 in txt2protect and 69 of 76 in the control condition.

The registry reports a primary chi-squared test with statistic 0.415 and p = .601. A simple unadjusted recalculation gives p = 0.519, with a risk-difference confidence interval spanning zero. Secondary outcomes include measures assessed at 3 weeks, with mixed results among the detailed comparisons. Safety entries report zero serious adverse events and zero deaths in both groups.

The record does not report the original sample-size justification, full statistical plan, multiplicity strategy, or complete missing-data procedures. The results describe retention and preliminary secondary measurements; they do not report a vaccination outcome.