Oral Health Literacy Tailored Communication: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Oral Health Literacy Tailored Communication (NCT01118143), a randomized na study. The primary outcome is Gingival Index.

2. Clinical Question

The trial record describes a broader interest in oral health literacy, attitudes, psychological factors, and oral health status. Its stated hypotheses include whether a structured intervention based on oral health literacy can change attitudes and improve oral health status. The primary outcome reported for this comparison is the gingival index, a continuous measure derived from tooth-level scores.

The numerical comparison is between the two instruction groups at the stated follow-up. It is not a direct test of every hypothesis listed in the study summary. For example, the registry record does not post outcome analyses of attitudes, psychological factors, or background knowledge. The posted result therefore addresses a specific question about gingival index rather than establishing the broader set of relationships proposed in the summary.

3. Trial Design

The registry record describes a randomized, single-masked, parallel-group trial of oral health instruction. One group received tailored oral health literacy instruction; the other received oral health instruction that was not tailored to literacy level. The record lists University of Tromso as the sponsor and gives the study status as completed. The recorded start is 2010-06 and primary completion is 2012-02.

The record lists enrollment of 179. For the primary gingival index outcome, the arm summaries report 64 participants in the individualized-instruction group and 69 in the ordinary-instruction group. These are the group counts attached to the posted outcome summaries; the registry record does not explain how they relate to the enrollment count, whether anyone lacked follow-up measurements, or which analysis population was used.

The primary outcome was assessed at six months after intervention. Plaque index is listed as a secondary outcome at the same follow-up. The record identifies two outcome measures and posts one secondary outcome. It does not post a detailed account of the randomization procedure, what the single masking designation refers to, intervention delivery or adherence, or the statistical analysis plan. Those details are not reported in the registry record.

This design compares group-level outcomes following randomized assignment. Randomization is intended, in general, to support a fair comparison by balancing factors across assigned groups on average. It does not guarantee that every characteristic is balanced in a particular trial, and the registry record does not report baseline characteristics with which to assess balance. The results should therefore be read as the numerical outcomes posted for the two assigned groups, with the limitations of the available reporting kept in view.

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: Enrolled participants: Total excluded n=46 * Not meeting the inclusion criteria (n=11) * Declined to participate (n=35)

Overall Study

Reasons for not completing this period:

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 Gingival Index, measured over 6 months after intervention.

The primary endpoint is the gingival index, measured in units on a scale and summarized as a mean with a standard deviation. The record says the individual index was obtained by adding tooth-level values, described as an average of four scores, and dividing by the number of teeth examined. It assigns score ranges of 0.1-1.0 to mild inflammation, 1.1-2.0 to moderate inflammation, and 2.1-3.0 to severe inflammation. The stated reference is Löe and Silness, 1963.

This index provides a numerical way to represent gingival inflammation across examined teeth. A group mean condenses the participant-level scores into a single summary, while the standard deviation describes how spread out individual scores are around that mean. The mean can aid comparison between randomized groups, but it does not show the distribution of individual values or how many participants fell into each score range.

The six-month timing makes the outcome a measure at a defined point after intervention. The registry record does not explain why this time point was selected, identify any other primary time point, or report details of examiner calibration or measurement reliability. Those details are not reported in the registry record. The index is an oral health measure; by itself, it does not describe every aspect of oral health or the experiences of participants.

7. Results Posted in the Registry

• Ordinary Oral Health Instruction: mean 1.12 versus 0.72 on control; difference 0.40 (95% CI 0.25 to 0.54), standardized effect d = 0.90; z-test p = <0.001.

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.

Plaque Index

• 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:
  • Ordinary Oral Health Instruction: mean 0.34 versus 0.08 on control; difference 0.26 (95% CI 0.17 to 0.35), standardized effect d = 0.97; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Ordinary Oral Health Instruction than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Plaque index is the one secondary outcome posted, measured at six months and summarized as a mean with a standard deviation. Its group summaries follow the same broad numerical direction as the primary endpoint: the mean is lower in the individualized-instruction group than in the ordinary-instruction group. This directional consistency can be considered alongside the primary result, but it does not make the two outcomes interchangeable. Gingival index and plaque index measure distinct aspects of oral health.

Secondary outcomes can provide additional context about a trial's findings, but they generally carry less confirmatory weight when their analysis plan and role are unclear. Testing multiple outcomes or comparisons creates more opportunities for at least one apparently notable finding, even if each individual test is interpreted at its nominal threshold. Whether and how this risk was addressed is not reported in the registry record.

The record lists two outcome measures and one posted secondary outcome, but it does not provide a multiplicity adjustment, a hierarchy of outcomes, or a prespecified strategy for interpreting secondary findings. The posted secondary result should therefore be treated as supportive descriptive evidence rather than as an independent confirmation of the primary comparison. The record also lists no reported analyses, so the timing and prespecification of the secondary analysis are not documented.

Agreement in direction across measures may be informative, but it cannot resolve questions about missing measurements, analysis populations, selective reporting, or statistical methods. Nor does it establish a shared mechanism. The registry record does not post analyses linking changes in plaque index to changes in gingival index at the participant level. The two endpoint summaries should be read as separate group comparisons.

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

• Plaque Index

9. Statistical Interpretation

10. Statistical Methods Explained

The posted primary outcome is continuous: it is a numerical score summarized by a mean and standard deviation in each group. A mean describes the central level of the observed scores, while a standard deviation describes their variability. The group summaries allow a direct unadjusted comparison of average index values. They do not show the full shape of either group's score distribution, and they do not identify how scores varied across individual participants.

What does the mean difference represent?

The comparison is defined as ordinary oral health instruction minus individualized oral health instruction. The reported mean difference is 0.396 units. Because the ordinary-instruction mean is higher, the difference is positive under that subtraction order. Stating the order matters: reversing it would reverse the sign without changing the underlying group contrast. The difference is in the gingival index's scale units, not a percentage change.

This difference is an unadjusted comparison of the posted group summaries. An unadjusted comparison does not account for other variables through a model. The registry record does not report an adjusted estimate or identify covariates used in an analysis. The distinction matters because unadjusted and adjusted analyses can answer related but not identical questions.

How should the p-value be read?

The posted unadjusted p-value is <0.001. In general, a p-value measures how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, the probability that the finding arose by chance, or a measure of effect size. A small p-value does not establish that a difference is important in practice.

The registry record does not describe the test used to produce a trial-authored p-value, and it lists no reported analyses. Accordingly, the p-value accompanying the summary-statistic comparison should be understood as an unadjusted result, not as confirmation of an undocumented prespecified analysis plan. The original analysis plan and whether any other analyses were conducted are not reported in the registry record.

What does the confidence interval add?

A confidence interval expresses uncertainty around an estimate. In general, a 95% confidence interval is generated by a procedure that, under its assumptions, would cover the target value in 95% of repeated samples. It is not a probability statement that this particular interval contains the true value. The interval for the mean difference extends from 0.248 to 0.545 units. Its endpoints describe a range of estimates compatible with the calculation procedure and data summaries, rather than all possible sources of uncertainty.

The interval is centered around an estimate of the group contrast, and its width conveys precision: a narrower interval indicates less sampling uncertainty than a wider interval under the same method and scale. It does not account automatically for limitations such as missing outcomes, measurement error, or a mismatch between the statistical model and the data. The registry record does not identify the method used to construct the interval or report checks of its assumptions.

What role does the standardized effect play?

The comparison statistics also include a standardized mean difference of 0.903, calculated using a pooled standard deviation of 0.439. Standardization expresses the mean contrast relative to variability, so it is not in the original index units. It can help describe the contrast on a scale that is less tied to the measurement units, but it does not replace the scale-specific difference or tell whether the difference is clinically important. The registry record does not state that this standardized measure was a planned trial endpoint or the basis of its original analysis.

The pooled standard deviation is a summary of within-group spread used in that standardization. The reported group standard deviations are 0.416 and 0.458. In general, variability affects the relationship between a raw mean difference and its standardized counterpart. A standardized statistic should therefore be interpreted alongside the original-scale outcome and with attention to the measurement's meaning.

Why can dispersion matter?

Standard deviations describe variation among participants. If outcomes vary substantially within groups, a given difference between means is less distinct relative to that variation. In general, over-dispersion means that observed variability is greater than a model assumes; standard errors and confidence intervals based on an inadequate variance model may then be misleading. The registry record does not report an over-dispersion assessment or a model-based analysis of the outcome. It is not possible to determine from the posted summaries whether such an issue was examined.

These methods describe the posted numerical comparison, not every stage of the trial analysis. The record does not report the original sample-size justification, allocation details beyond randomized parallel groups, analysis population, missing-data method, or multiplicity procedure. Those omissions limit assessment of whether the reported summary comparison was planned and whether its uncertainty accounts for all relevant design and analysis features.

11. Confidence Intervals and Precision

The primary mean difference is 0.396 index units, and its 95% confidence interval runs from 0.248 to 0.545. This interval communicates sampling precision around the unadjusted contrast more directly than the p-value alone. Its lower and upper limits are both above zero, consistent with an observed higher mean in the ordinary-instruction group given the stated subtraction order.

Precision is not the same as accuracy. A confidence interval can be narrow while still being affected by biases or assumptions not reflected in its calculation. The registry record does not report the interval method, missing-data handling, or sensitivity analyses. Thus, the interval captures only the uncertainty represented by its calculation, not every potential source of uncertainty in the trial.

The arm summaries include 64 participants for individualized instruction and 69 for ordinary instruction. The record does not say whether these counts represent all randomized participants with available measurements, an analysis population defined in advance, or another selection. Without that information, the precision of the posted comparison cannot be evaluated in relation to possible loss of outcome data or exclusions.

Statistical precision also does not decide practical importance. The registry record gives no minimally important difference for the gingival index. The interval therefore describes plausible values for the group contrast under the calculation assumptions, but it does not classify those values as clinically meaningful or unimportant. The index ranges are described in terms of inflammation severity, yet the mean difference does not provide counts of participants in each severity category.

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 sample-size figures are planning illustrations based on the observed effect, not a record of the trial's original design calculation. For this continuous outcome, the figures are participants per arm, not total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect defined as the stated fraction of the observed effect. The trial's own original design assumptions are not reported in the registry record.

Rows describing 100%, 75%, and 50% of the observed effect ask how many participants per arm would be needed to plan for effects of those relative sizes under the listed assumptions. The 80% power column gives the estimated per-arm sample size for a design with an 80% chance of detecting the specified effect if that effect is real and the assumptions hold. The 90% power column makes the analogous calculation for a 90% chance. These are design probabilities, not guarantees about any one study.

As the target effect becomes smaller, it is harder to distinguish from random variation, so the planning calculation calls for more participants per arm. The figures are hypothetical planning aids based on the observed effect and the stated assumptions. They are not observed power, do not describe the power achieved in this trial, and do not establish that the original trial was designed around the observed result.

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 = 0.396; pooled standard deviation σ = 0.439.
2. n = 2 × (1.96 + 0.842)² × 0.439² / 0.396² = 19.2, rounded up to 20 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 <- 0.3962                      # observed difference in means
sigma <- 0.438505747831975                     # 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(1118143)
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 = 20 (80% power), 26 (90% power)
 75% of observed effect: n per arm = 35 (80% power), 46 (90% power)
 50% of observed effect: n per arm = 77 (80% power), 103 (90% power)
power.t.test: 20.2 
Simulated power at n = 20 per arm: 0.794 (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

Multiplicity arises when a study evaluates more than one outcome, time point, subgroup, or statistical comparison. In general, the more comparisons considered, the greater the chance that at least one result will appear notable by chance if each is judged without accounting for the full set. A prespecified outcome hierarchy or adjustment method can help define how results should be interpreted. The registry record lists two outcome measures and one secondary outcome, but a multiplicity strategy is not reported.

The record gives no detailed statistical analysis plan, no account of which outcomes were designated primary before data collection, and no explanation of whether additional time points or subgroup analyses were considered. It also lists no reported analyses. The available information therefore does not establish what analyses were conducted beyond the posted outcome summaries, or whether the comparisons were planned before results were known. These details are not reported in the registry record.

Missing-data handling is also not described. The primary outcome summaries list 64 and 69 participants in the respective arms, while the overall enrollment is 179. The record does not explain the relationship between these counts, whether outcome measurements were unavailable, or why the arm counts differ from the enrollment total. No imputation method, sensitivity analysis, or account of missingness is posted. It is not possible to determine whether missing outcomes could have affected the estimates.

The analysis population is not reported. The registry record does not say whether participants were analyzed according to randomized assignment, whether any participants were excluded after randomization, or whether the analysis was limited to participants with measured outcomes. A reader therefore cannot assess whether the posted comparisons follow an intention-to-treat approach or another population definition.

These omissions do not show that a particular analysis or procedure was absent; they mean that it cannot be evaluated from the registry record. Clear reporting of multiplicity, analysis populations, and missing-data methods would help distinguish confirmatory results from exploratory ones and clarify the assumptions behind the reported comparisons.

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 0% reporting threshold.

The serious adverse event figures list zero affected participants among 64 at risk in the individualized-instruction group and zero among 69 at risk in the control group. The other adverse event figures also list zero affected participants among 64 and 69 at risk, respectively. These counts describe what is posted for the groups and categories shown; they do not establish that no events occurred outside the registry's reporting definitions or observation period.

The deaths fields are not populated with counts, so deaths are not reported in the registry record. The record does not provide event descriptions, severity definitions, follow-up duration for safety, or details about how adverse events were collected. Zero reported events should not be interpreted as proof of no risk, particularly without the reporting methods and observation context. The figures are a limited account of reported safety outcomes, not a complete assessment of safety.

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

The posted results show a lower mean gingival index in the individualized-instruction group than in the ordinary-instruction group at six months. The unadjusted difference is 0.396 units, and the 95% confidence interval is 0.248 to 0.545. This describes the group-level pattern and the precision of the estimated contrast under the interval's assumptions. It does not establish what happened to every participant.

The randomized design is relevant because, in general, random assignment can support a causal comparison when allocation is implemented appropriately and outcomes are analyzed in a way that preserves the comparison. The registry record does not report enough detail about allocation, outcome availability, analysis populations, or statistical methods to evaluate all of those conditions. The posted contrast should therefore be described as an observed between-group result, not as definitive proof of a causal effect.

The record does not provide a threshold for a clinically important change in gingival index. Statistical evidence against a zero difference cannot determine whether the magnitude matters to patients or dental practice. The outcome is a scale derived from examined teeth, and the mean difference cannot be converted into a count of people who changed severity category without participant-level results.

The listed hypotheses concern a broader set of questions about literacy, attitudes, psychological factors, and oral health. The posted primary outcome addresses only the mean gingival index at six months. The record does not post analyses establishing associations among those other factors or explaining how any changes occurred.

Finally, the registry's adverse-event figures record zero affected participants in the listed categories, while deaths are not reported in the registry record. Given the absence of further safety collection details, those figures should be read as a description of recorded events rather than as proof that the intervention has no risk. The results neither warrant medical advice nor replace consideration of the full trial report, which is not identified in the registry record.

17. Why This Trial Matters Statistically

This trial is statistically informative as an example of how a continuous clinical outcome can be compared between randomized groups using arm means, variability, a mean difference, and a confidence interval. The original scale difference communicates the contrast in gingival index units, while a standardized difference expresses it relative to pooled variability. These summaries address related but distinct questions and should not be treated as substitutes.

The record also illustrates why statistical evidence and clinical meaning are separate. The unadjusted confidence interval excludes zero, but the registry record does not define a clinically important threshold. Without such a benchmark, a reader can assess the direction and precision of the estimate but cannot classify its practical importance from the posted numbers alone.

Another important issue is the gap between an enrollment count and the counts attached to outcome summaries. The record lists enrollment of 179 and outcome group counts of 64 and 69, without explaining the relationship. This does not by itself identify a problem, but it leaves important questions about the analysis population and availability of measurements unanswered. Reporting participant flow and missing-data methods would make the results easier to evaluate.

The trial record describes a broader set of hypotheses than the outcome analyses it posts. That contrast highlights the value of clear reporting about prespecified outcomes, multiplicity, and analysis methods. Even when an estimate appears precise, uncertainty about how it was selected and analyzed affects how strongly it can support a conclusion.

Finally, planning illustrations based on observed effects can help readers understand the sample sizes that hypothetical future studies might require under stated assumptions. They do not explain the trial's original design or its achieved power. Keeping planning calculations separate from the observed trial result is essential for a sound statistical reading.

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.

Important design and analysis details are not reported in the registry record. These include the randomization procedure, the meaning of the single-masking designation, the original sample-size justification, and the full statistical analysis plan. Without these details, it is not possible to establish whether the posted comparisons match prespecified methods or to assess all features that may influence bias and uncertainty.

The primary outcome summaries include fewer participants in the arm-level counts than the overall enrollment count, but the record does not explain participant flow or why the counts differ. Missing outcome data, exclusions, and the analysis population are not described. The effects of any unavailable measurements on the group comparison therefore cannot be assessed.

The record does not post baseline characteristics, intervention adherence, or details of how instruction was delivered. It also does not report measurement reliability or examiner procedures for the gingival index. These omissions limit assessment of group comparability, implementation, and outcome measurement. They do not prove that any specific problem occurred; they limit what can be concluded from the registry record.

The primary comparison is unadjusted, and no adjusted analysis is posted. The record does not state whether other outcomes, time points, or subgroup comparisons were evaluated or how multiplicity was handled. It lists no reported analyses. Selective analysis or reporting cannot be assessed from this information, but neither can it be ruled out.

The primary result is a group mean difference at one stated follow-up point. The record does not provide participant-level distributions, a clinically important difference threshold, or results for the broader hypotheses about attitudes and literacy. The adverse-event listing also lacks details on collection methods and follow-up, and deaths are not reported in the registry record. These reporting limits call for a restrained interpretation of both benefits and safety.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Oral Health Literacy Tailored Communication — NCT01118143.
• Registry record last updated 2015-04-16; status last verified 2015-03.
• Results first posted 2015-03-23.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT01118143 is a completed randomized, single-masked, parallel-group trial sponsored by University of Tromso. It compared tailored or individualized oral health instruction with ordinary instruction in adult dental patients. Enrollment was 179; the registry record lists the primary gingival index outcome at six months after intervention.

The posted arm means were 0.719 for individualized instruction and 1.115 for ordinary instruction. The unadjusted mean difference was 0.396 units, with a 95% confidence interval from 0.248 to 0.545 and an unadjusted p-value of <0.001. Plaque index is posted as a secondary outcome. The record does not report an analysis plan, analysis population, missing-data method, or multiplicity strategy; deaths are not reported in the registry record.