Online MBCT Program for University Students: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Online MBCT Program for University Students (NCT05804877), a randomized na study. The primary outcome is BDI-II -Pretest.

2. Clinical Question

The trial's stated purpose was to examine whether the online program could reduce depressive symptoms and increase quality of life among university students with depressive symptoms. The intervention and comparison groups received different content but were described as having the same delivery platform and schedule. That setup makes a comparison between groups relevant to the stated questions in principle, but the reported primary endpoint is measured before either program begins. It therefore cannot by itself answer whether depressive symptoms changed during the intervention or whether one program produced a different post-intervention result.

The registry lists BAI, OSA, and COPM measures among the secondary outcomes, each with pre-test and post-test entries. The numerical secondary results posted for BAI include a pre-test and a post-test comparison. Numerical results for OSA and COPM are not reported in the registry record. Results on acceptance and practicability are also not reported in the registry record. The distinction between the stated research questions and the results actually posted is essential to interpreting what can be learned from this record.

3. Trial Design

This completed study is listed as randomized, with a parallel-group model and no masking. The registry records enrollment of 69. It identifies Chung Shan Medical University as the sponsor. The study start is listed as 2023-04-20 and primary completion as 2023-07-05. The phase is listed as NA.

The experimental group was assigned an online mindfulness-based cognitive therapy program, while the control group received mental health education. Both programs were delivered through LINE 3 times a week for 8 weeks. The registry describes the control education as intended to help participants manage negative emotions. More detailed information about how randomization was carried out, whether allocation was concealed, adherence, or deviations from the assigned program is not reported in the registry record.

Several reported outcome counts differ across measures: the primary BDI-II baseline entries list 23 participants in each arm, while the BAI pre-test entries list 26 in each arm and the post-test entries list 23 in each arm. The safety record lists 26 participants at risk in each group. These are measure-specific registry figures; the record does not explain the differences. It is not possible to infer from these entries how many participants completed each activity or why some measures have different counts.

The primary outcome entry is BDI-II score at pre-test, specified as one week before intervention. The registry does not post a primary post-intervention BDI-II result or a reported analysis. Thus, although the study is a randomized parallel-group trial and the stated aim concerns program effects, the posted primary measure is a baseline measure rather than a reported endpoint after treatment.

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: Participants who (1) have a psychiatric diagnosis, (2) are currently receiving counseling, (3)are not from the medical university in Taiwan, and (4) are unwilling to participate in the study will be excluded.

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 BDI-II -Pretest, measured over BDI-II score at pre-test (1week before intervention).

The primary outcome entry is the Beck Depression Inventory II (BDI-II) score at pre-test, one week before the intervention. The BDI-II is described in the registry as a 21-item self-report questionnaire designed to measure the level of severity of depressive disorders. Items are scored from 0 to 3, and higher scores indicate greater symptom severity. It is therefore a measure of symptom severity, not a direct measure of whether a program was accepted or practicable.

The registry describes scores below 13 points as indicating no or minimal depressive symptoms, scores between 14 and 19 as indicating a mild expression of depressive symptoms, scores between 20 and 28 as indicating moderate severity, and scores between 29 and 63 as evidence of severe depressive disorder. Those descriptions provide a way to understand the scale, but the primary result is a group mean and standard deviation; it does not report how many individuals fell into each category.

A baseline BDI-II measure can describe the groups before the intervention and provide context for their starting symptom scores. To assess change associated with the programs, an outcome measured after the intervention or an analysis comparing change over time would be needed. A post-intervention primary BDI-II result or such an analysis is not reported in the registry record. Accordingly, the posted primary endpoint does not establish whether depressive symptoms changed during the program.

7. Results Posted in the Registry

• mental health education: mean 14.42 versus 12.54 on control; difference 1.88 (95% CI -4.43 to 8.19), standardized effect d = 0.17; z-test p = 0.559.

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.

BAI -Pretest

• 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:
  • mental health education: mean 8.65 versus 9.31 on control; difference -0.66 (95% CI -4.74 to 3.42), standardized effect d = -0.09; z-test p = 0.751.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between mental health education and the control. The interval gives the range of effects that remain compatible with the data.

BAI -Posttest

• 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:
  • mental health education: mean 6.52 versus 5.52 on control; difference 1.00 (95% CI -3.08 to 5.08), standardized effect d = 0.14; z-test p = 0.631.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between mental health education and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes listed in the registry include BAI, OSA, and COPM scores at pre-test and post-test. Numerical summaries and comparisons are posted for BAI at the two time points. Numerical results for OSA and COPM are not reported in the registry record. The available secondary results therefore cover only part of the outcome set named in the record.

Across the two BAI comparisons, the point estimate changes direction from pre-test to post-test: the pre-test mean difference is -0.66 and the post-test mean difference is 1.0. The confidence interval at each time point includes zero, and the unadjusted p-values are 0.751 and 0.631, respectively. These are comparisons between groups at separate time points, not a reported analysis of change within participants or a direct test of whether group trajectories differ.

The primary result is a BDI-II baseline comparison, not a post-intervention outcome. The secondary BAI post-test summary therefore adds a later time-point comparison on a different measure, but it does not resolve the absence of a reported primary post-intervention BDI-II result. It also cannot establish a change in depressive symptoms without a suitable analysis and supporting information about the participants contributing to each time point.

Unadjusted secondary results generally carry less weight than a prespecified primary analysis because multiple outcomes and time points create more opportunities for chance findings. General statistical explanation: when many comparisons are examined, the chance of at least one apparently notable result can increase unless multiplicity is addressed. The registry does not report a multiplicity plan, and the posted secondary results are not accompanied by reported analyses. These results are best treated as descriptive and exploratory rather than as independent confirmation of a program effect.

The registry's stated aims also include quality of life, acceptance, and practicability. The existence of outcome names does not establish that results for those questions were posted. Without the numerical OSA and COPM results or findings on acceptance and practicability, the available secondary record cannot support a broad conclusion about all of the stated aims.

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

• BAI -Pretest
• BAI -Posttest
• OSA -Pretest
• OSA -Posttest
• COPM -Pretest
• COPM -Posttest

9. Statistical Interpretation

10. Statistical Methods Explained

The registry identifies the study as randomized and parallel-group, with no masking. In a parallel-group design, participants are assigned to one of the study groups and remain in that group for the comparison. Randomization is generally used to reduce systematic differences between groups at assignment. This is a general explanation; the method used to generate the allocation sequence and whether allocation was concealed are not reported in the registry record. With no masking, participants and study personnel were not masked according to the registry entry. Further details about who knew group assignments are not reported.

What do the reported summaries describe?

The primary outcome is a continuous score, and the registry presents each group's mean and standard deviation. A mean describes the average score in the reported group. A standard deviation describes how dispersed individual scores are around that average. These statistics summarize the group distribution, but they do not show the full distribution or the individual participants' score changes.

The reported primary comparison is a mean difference between mental health education and the online mindfulness-based cognitive therapy group. The posted difference is 1.88, and the comparison is oriented as mental health education relative to the online program. On the BDI-II, higher scores indicate greater symptom severity. However, the measure was collected at pre-test, so the difference describes the groups before intervention, not the effect of one program compared with the other.

How should the confidence interval be understood?

A confidence interval gives a range of values compatible with the data and the statistical procedure used to construct it. General statistical interpretation: a narrower interval indicates greater precision, while a wider interval indicates greater uncertainty about the size and direction of the underlying difference. The primary comparison's 95% confidence interval runs from -4.432 to 8.192 and includes zero. It therefore does not pin down a single direction for the baseline mean difference. The interval does not directly quantify uncertainty about a treatment effect because the primary outcome is measured before intervention.

The registry also lists an unadjusted p-value of 0.559 for that comparison. A p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the test assumptions held. It is not the probability that the null hypothesis is true, nor is it a measure of the probability that the intervention works. The registry does not report a sponsor analysis or a specific statistical testing plan for this endpoint.

What is not available about the analysis?

The record lists zero reported analyses. It does not report a statistical analysis plan, a model for repeated measurements, adjustment for baseline scores, handling of missing data, or the population included in each analysis. The original trial's sample-size justification and any interim analyses are not reported in the registry record. These omissions matter because they prevent assessment of whether the posted comparisons reflect prespecified analyses, how incomplete measurements were handled, or whether the reported results account for other variables.

General statistical explanation: repeated measurements on the same participants are related, so an analysis of change should account for that within-participant relationship. A comparison of post-test means alone and a comparison of changes from baseline answer different questions. The registry posts summaries at particular time points, but does not report a change analysis for BAI or a post-test primary BDI-II comparison. No particular analysis method should be inferred from the summaries.

Why does variability matter?

The standard deviations indicate substantial spread in scores relative to the group means. General statistical explanation: high variability makes it harder to estimate a group mean or a difference precisely, especially when the number of observations is limited. Over-dispersion is a concern when observed variability is greater than a statistical model allows; if that happens, standard errors can be too small and intervals can be too narrow. The registry does not identify a count model or report an over-dispersion assessment, and the primary outcome is a continuous score, so over-dispersion should not be presumed to apply to this analysis.

The posted comparison and interval are useful descriptive summaries, but they do not replace missing information about the analysis population, missingness, adherence, or adjustment. General statistical explanation: an unadjusted comparison uses the reported group summaries without accounting for additional covariates. Such a comparison can be informative but may not answer the same question as a prespecified adjusted analysis. Whether an adjusted analysis was conducted is not reported in the registry record.

11. Confidence Intervals and Precision

The primary baseline mean difference is 1.88, with a 95% confidence interval from -4.432 to 8.192. The interval crosses zero and includes both negative and positive differences. Thus, the posted summary does not precisely establish which group had the higher average BDI-II score at baseline. The interval is also not an interval for the program's effect, because the BDI-II measure was collected one week before intervention.

A confidence interval expresses uncertainty about an estimated quantity under the statistical procedure used. General statistical explanation: a confidence interval is more informative than a point estimate alone because it displays a range of values that remain compatible with the observed data and assumptions. It should not be read as a range containing a fixed proportion of individual scores; the standard deviations, rather than the interval for the mean difference, describe variation among individual scores.

The BAI pre-test comparison is -0.66, with a 95% confidence interval from -4.74 to 3.42. The BAI post-test comparison is 1.0, with a 95% confidence interval from -3.076 to 5.076. Both intervals include zero, and neither provides a narrowly determined direction of the group difference. These are separate time-point comparisons; the record does not report an interval for change between time points.

The registry does not report a threshold for a clinically important difference on these measures. As a result, the confidence intervals cannot be classified against a stated threshold for meaningful change. Their interpretation is further limited by the absence of a posted primary post-intervention BDI-II comparison and by the lack of reported analysis details.

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 planning figures are participants per arm, not total participants or total events. The record describes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect. These are planning assumptions for the illustration; the original trial's design assumptions are not reported in the registry record.

For the primary comparison, planning for 100% of the observed effect gives 530 participants per arm for 80% power and 710 participants per arm for 90% power. Planning for 75% of the observed effect gives 942 participants per arm for 80% power and 1,261 participants per arm for 90% power. Planning for 50% of the observed effect gives 2,119 participants per arm for 80% power and 2,837 participants per arm for 90% power.

In plain terms, the 80% power column represents a planned chance of detecting the specified effect under the stated assumptions if that effect is present. The 90% column represents a higher planned chance of detection for the same specified effect, and therefore requires more participants per arm in these illustrations. Smaller effects need more participants to detect reliably, which is why the figures rise as the chosen fraction of the observed effect becomes smaller.

The curve expresses the same planning relationship between the effect size targeted and the number of participants needed, under the stated assumptions. These counts are a planning illustration based on the observed comparison, not a description of the trial's actual design or its achieved statistical power. They are not observed power. The primary observed comparison is a pre-intervention difference, so these planning values should not be read as a sample-size justification for detecting a post-intervention treatment effect.

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 = 1.880; pooled standard deviation σ = 10.921.
2. n = 2 × (1.96 + 0.842)² × 10.921² / 1.880² = 529.7, rounded up to 530 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 <- 1.88                      # observed difference in means
sigma <- 10.9212201699261                     # 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(5804877)
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 = 530 (80% power), 710 (90% power)
 75% of observed effect: n per arm = 942 (80% power), 1,261 (90% power)
 50% of observed effect: n per arm = 2,119 (80% power), 2,837 (90% power)
power.t.test: 530.7 
Simulated power at n = 530 per arm: 0.802 (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 multiple outcome measures, including a primary BDI-II entry and secondary BAI, OSA, and COPM measures at pre-test and post-test. It does not report how the primary outcome was selected from the listed measures, whether additional time points or outcomes were prespecified, or whether the analysis plan adjusted for multiple comparisons. Multiplicity handling is not reported in the registry record.

General statistical explanation: examining several outcomes, time points, or contrasts can increase the chance that at least one result appears notable by chance. A prespecified primary endpoint and a stated multiplicity strategy help readers distinguish confirmatory tests from exploratory comparisons. Without those details, isolated secondary p-values should not be treated as if they independently confirm the study's main question. The unadjusted p-values posted for BAI are therefore interpreted as unadjusted comparisons, not as multiplicity-controlled evidence.

The record contains different counts for the BDI-II, BAI, and safety entries. It does not explain missing measurements, withdrawals, exclusions, or whether analyses included all randomized participants. The method used to handle missing data is not reported in the registry record. General statistical explanation: if participants with missing outcomes differ systematically from those with observed outcomes, analyses limited to observed scores may not represent the randomized groups fairly. The direction or extent of any such effect cannot be determined from the posted information.

The record also does not report whether the analysis population was intention-to-treat, per-protocol, or another defined group. Adherence to the online sessions, crossovers, and deviations from assigned programs are not reported in the registry record. These details would help clarify how closely the analyzed groups correspond to the randomized groups and what comparison the results represent.

No reported analyses are listed. The statistical analysis plan, model specification, any baseline adjustment, and any interim analyses are not reported in the registry record. These absences prevent a full assessment of prespecification, missing-data handling, and the intended inferential framework. They do not establish that such procedures were absent; they mean that they cannot be evaluated from this registry record.

15. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists 26 participants at risk for serious adverse events in the online mindfulness-based cognitive therapy group and 26 in the mental health education group. It records zero serious adverse events in each group. It also records zero other adverse events and zero deaths in each group. No serious adverse event terms are listed.

These figures describe the events recorded in the registry for the stated groups and participants at risk. They do not show that no event of any kind occurred outside the categories or reporting period captured by the record, and they do not establish that the programs are free of risk. The safety counts are also different from the counts shown for some outcome measures; the registry does not explain the difference.

The registry does not report further details about event definitions, collection procedures, severity, relationship to the programs, or the period used for safety follow-up. Consequently, the figures should be read narrowly as the posted counts, rather than as a complete account of safety monitoring or as a comparison with sufficient detail to characterize uncommon events.

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

The posted primary data describe pre-intervention BDI-II scores in the two randomized groups. The mean difference is 1.88, with a 95% confidence interval from -4.432 to 8.192 and an unadjusted p-value of 0.559. Because the score was recorded one week before the intervention, these statistics do not estimate whether the mindfulness-based program changed depressive symptoms or differed from mental health education after the program.

The BAI secondary entries provide group summaries at pre-test and post-test, but the registry does not report a direct analysis of change or a primary post-intervention BDI-II comparison. The posted BAI confidence intervals include zero. Results for OSA and COPM, and findings on acceptance and practicability, are not reported in the registry record. The available results therefore address only a limited part of the questions the study set out to examine.

These results do not establish that the programs are equivalent. A failure to distinguish group means in a particular comparison is not proof that the groups have the same outcomes. General statistical explanation: demonstrating equivalence or non-inferiority requires a suitable design, prespecified margins, and corresponding analyses. Those are not reported in the registry record.

Likewise, the absence of reported serious adverse events in the listed groups should not be interpreted as proof that no risks exist. The registry records zero serious and other adverse events and zero deaths, but its safety details are limited. The record also does not provide enough analysis information to assess missing data, adherence, or the population included in each analysis.

The defensible interpretation is descriptive: the registry posts baseline BDI-II group means and a comparison with substantial uncertainty, and it posts selected BAI summaries at two time points. Those statistics alone do not answer whether the online program reduces depressive symptoms, increases quality of life, or is acceptable and practicable. A fuller evaluation would require reported post-intervention primary results and clear analyses that address the study's stated questions.

17. Why This Trial Matters Statistically

This record illustrates why the timing and definition of an endpoint matter as much as the name of the measure. BDI-II is a measure of depressive symptom severity, and the registry identifies it as the primary outcome. But the listed timeframe is pre-test, one week before intervention. A baseline comparison can describe the starting groups; it cannot by itself estimate what happened after the programs began. Readers should check the outcome timeframe before interpreting a result as evidence about treatment response.

The record also demonstrates the difference between having outcome names listed and having analyzable results posted. BAI, OSA, and COPM are named as secondary measures at pre-test and post-test, but numerical results are available only for BAI in the record. Quality of life, acceptance, and practicability are part of the stated aims, yet findings on those questions are not reported in the registry record.

Statistically, the distinction between a point estimate and its precision is central. The primary comparison's confidence interval extends across zero, while the posted groups have substantial score variability. The summary does not support a precise conclusion about the direction of the baseline difference, much less a precise conclusion about a program effect. This is an example of why p-values alone are insufficient and why uncertainty intervals and endpoint timing should be considered together.

Finally, the sample-size illustrations depend on an observed contrast and explicit planning assumptions, but the record does not report the original design justification. Since the primary observed contrast is at baseline, interpreting it as a basis for planning a future efficacy study requires particular caution. The registry record is useful for distinguishing what was intended from what is numerically posted and for identifying the information needed for a stronger inferential assessment.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most important trial-specific limitation in the posted results is that the primary BDI-II measure is a pre-test score, not a reported post-intervention outcome. The registry's stated questions concern reducing depressive symptoms and increasing quality of life, but the primary result presented does not directly assess change after the intervention. A primary post-intervention BDI-II result and a reported analysis of change are not reported in the registry record.

Numerical secondary results are limited to BAI pre-test and post-test comparisons. Although OSA and COPM are listed among the secondary measures, their numerical results are not reported in the registry record. Results on program acceptance and practicability are also not reported. This limits how much of the stated research agenda can be assessed from the posted data.

Participant counts differ across the posted outcome and safety entries, and the record does not explain the differences or describe missing-data handling. Analysis populations, adherence, withdrawals, exclusions, and any deviations from assigned programs are not reported in the registry record. Those omissions make it difficult to assess how the available summaries relate to the randomized groups.

The registry does not report the original sample-size justification, a statistical analysis plan, multiplicity handling, or the methods used to generate and conceal randomization. It also provides limited detail about safety-event collection. These are limitations of what can be evaluated from the record; they do not establish that the procedures were not conducted. The study is listed as having no masking, which may matter for self-reported outcomes, but the record does not provide further detail about how that issue was addressed.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Online MBCT Program for University Students — NCT05804877.
• Registry record last updated 2025-12-10; status last verified 2025-11.
• Results first posted 2025-12-10.
• 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 identifies a completed randomized, parallel-group study of an online mindfulness-based cognitive therapy program compared with mental health education for university students with depressive symptoms. Both programs were delivered through LINE 3 times a week for 8 weeks, and the study is listed as unmasked.

The primary outcome entry is BDI-II score one week before intervention. The posted mean difference is 1.88, with a 95% confidence interval from -4.432 to 8.192 and an unadjusted p-value of 0.559. This is a baseline comparison, not a reported estimate of treatment effect. BAI summaries are posted at pre-test and post-test; numerical results for OSA and COPM are not reported in the registry record. The record lists zero serious adverse events, zero other adverse events, and zero deaths in each group, among 26 participants at risk per group.

The registry does not report a primary post-intervention BDI-II result, a reported analysis plan, or the original sample-size justification. The available data are therefore descriptive and do not resolve the study's stated questions about symptom reduction, quality of life, acceptance, or practicability.