Study of Mattress Type in Fibromyalgia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Mattress Type in Fibromyalgia (NCT01108718), a randomized na study. The primary outcome is Mattress Preference of Fibromyalgia Patients.

2. Clinical Question

The study’s purpose was to determine whether a new mattress relieves fibromyalgia symptoms and improves sleep, and whether one mattress type is preferred over the other. The primary outcome description says participants rated each test mattress based on sleep quality and symptom severity, then ranked the mattresses by preference at the end of the study. This makes preference a participant-reported judgment, while sleep monitoring and symptom assessment provide other kinds of information about the experience of each mattress.

The registry record identifies the study as randomized and crossover. In general, a crossover design lets each participant receive more than one intervention, so comparisons can reflect responses within the same participant as well as differences between treatment periods. The two sequence descriptions indicate that participants received the mattresses in different orders. The record does not report the randomization procedure or whether a washout period occurred. It also does not report the actual preference result, so the stated research question cannot be answered from the posted results alone.

3. Trial Design

The registry record describes a randomized, quadruple-masked crossover study, with enrollment of 12. Its status is completed. The study began in 2009-07, and primary completion was recorded in 2010-10. The phase is listed as NA. Beth Israel Medical Center is named as sponsor.

The two sequence descriptions specify that participants either received the Tempur-Pedic mattress first and then the control mattress, or received the control mattress first and then the Tempur-Pedic mattress. Each mattress intervention is described as lasting 2 months. The record’s primary outcome timeframe is 6 months. It does not explain the timing of any intervals between mattress periods, so the presence or length of a washout period is not reported in the registry record.

In general, crossover designs differ from parallel-group trials because participants experience multiple interventions rather than remaining in one assigned group. This can make within-participant comparisons useful, but interpretation depends on the treatment order, period effects, and whether an earlier intervention could affect responses during a later period. Randomized sequence allocation can help balance order, but the record does not describe the sequence-generation method, allocation concealment, or how the analysis accounted for order and period.

The study is described as quadruple-masked, but the registry record does not identify which roles were masked or how masking was maintained. It also does not report the protocol, a sample-size justification, interim analyses, or a detailed statistical analysis plan. Completion status indicates that the study was marked completed; it does not, by itself, establish that every planned assessment was available or that the primary outcome was reported.

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: Subjects who displayed the existence of a previously undiagnosed sleep disorder were excluded from study participation.

Received First Intervention (2 Months)

Received Second Intervention (2 Months)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Following 2 months use of each test mattress, the study patients' sleep patterns and severity of fibromyalgia symptoms were assessed. At the end of the study, study patients were asked to rate each mattress in order of preference.

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 Mattress Preference of Fibromyalgia Patients, measured over 6 months.

The primary outcome is titled “Mattress Preference of Fibromyalgia Patients” and is expressed as a percentage of study participants. According to its description, participants rated each test mattress after 2 months of use, considering sleep quality and severity of fibromyalgia symptoms. At the end of the study, they were asked to rate the mattresses in order of preference. Preference therefore captures participants’ overall stated ranking after experience with both mattress types; it is not the same measure as an objective sleep recording or a symptom scale.

The record also describes polysomnography (PSG), with sleep stages monitored and scored according to how much they reflect a normal sleep pattern. Changes in fibromyalgia symptom severity were assessed using chi-squared and t-test methods. These descriptions indicate that sleep and symptoms were also considered, but the registry record does not report their numerical results or clarify how they relate analytically to the preference outcome.

Preference can be useful when a study asks which option participants favor after trying each one. However, a percentage needs a defined numerator and denominator to be interpreted, and the posted record does not provide a preference count, percentage, uncertainty interval, or comparative estimate. The registry record lists the endpoint and its measurement approach, but does not report the primary outcome result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record names chi-squared and t-test methods for assessing changes in fibromyalgia symptom severity. It does not give enough detail to determine the exact variables, hypotheses, model specification, or analysis population for either test. The primary outcome is described as mattress preference, but the record does not give a statistical test or effect estimate for that endpoint. The distinction matters: knowing that a method was named does not establish which specific contrast was tested or what the result was.

In general, a t-test evaluates evidence about a difference in means under assumptions appropriate to the data and design. A chi-squared test evaluates whether categorical counts are compatible with a specified pattern of association or difference. The record does not state whether symptom severity was analyzed as a continuous or categorical measure for each test, nor how repeated observations from the crossover periods were represented. It would be speculative to infer those choices from the names of the tests alone.

For a crossover study, measurements from the same participant are related rather than independent. In general, analysis should account for that within-participant structure when comparing treatments. Treatment period and sequence can also matter. For example, an apparent treatment contrast may be affected by a systematic change over time or by an effect that carries into a later period. The registry record does not report whether the sponsor examined period, sequence, or carryover effects, or whether the stated tests were adapted to account for repeated observations.

Polysomnography is described as a way to monitor sleep stages and score how closely they reflect a normal sleep pattern. That identifies a measurement process, not a complete statistical method. The record does not specify which PSG measures were analyzed, how scores were summarized, whether scoring was performed without knowledge of treatment, or how any missing recordings were handled. The record also does not post PSG results. The sleep monitoring description should therefore not be read as evidence of a particular sleep effect.

A confidence interval, in general, expresses the range of estimates compatible with the data and the method used, under its assumptions. Its width conveys precision: narrower intervals indicate more precise estimates, while wider intervals indicate greater uncertainty. A p-value, in general, describes how unusual the observed data would be under a specified null hypothesis and model. Neither measure is a substitute for the effect estimate itself, and neither can be interpreted without knowing the comparison and analysis. The registry record does not report a confidence interval or p-value for the primary outcome.

Over-dispersion is a general concern when count data vary more than a statistical model expects. If present, standard errors from a model that assumes less variability may be too small, making intervals too narrow and tests too optimistic. The record does not identify an over-dispersion model or provide enough outcome data to assess whether over-dispersion was relevant. This is a general consideration, not a claim about the study’s data.

Randomization is intended, in general, to make treatment sequence assignment independent of participant characteristics, subject to the method used and the size of the study. The registry says allocation was randomized, but does not describe sequence generation or concealment. Masking is listed as quadruple; the record does not say which parties were masked or explain how the mattresses were presented. These details can affect how confidently readers assess protection against selection and measurement biases.

The enrollment is recorded as 12. The record does not state a sample-size justification, assumptions used in planning, or a target effect. Any planning illustration based on an observed effect would be a retrospective calculation and not the study’s original design rationale. Sample-size illustrations are planning aids, not observed power and not evidence that the trial did or did not detect an effect. No such reasoning can be attributed to the investigators from the registry record.

The record lists one outcome measure and one analysis, but the primary outcome result is not reported. It also does not give a protocol or detailed analysis plan with which to judge prespecification, outcome changes, or selective reporting. A named test is not enough to reconstruct the analysis, and no missing estimate should be inferred from the study description.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and one analysis, and identifies mattress preference as the primary outcome. It does not describe a plan for controlling multiplicity across outcomes, comparisons, time points, or statistical tests. The study description nevertheless refers to preference, PSG sleep monitoring, and changes in fibromyalgia symptom severity. It is not reported in the registry record whether these were treated as separate endpoints, exploratory measures, or components of a prespecified testing strategy.

In general, testing multiple outcomes or contrasts can increase the chance of finding at least one apparently notable result by chance. A prespecified hierarchy or adjustment can help address that issue, but neither should be assumed: the registry record does not report the relevant plan or adjustment method. The absence of a reported multiplicity strategy does not show that no strategy existed; it means the registry entry does not document one.

Missing-data handling is also not reported in the registry record. The entry does not describe missing ratings, incomplete PSG recordings, withdrawals, or how participants with incomplete crossover periods were handled. It does not state whether the analysis included all randomized participants, only those with observations for both mattresses, or another analysis population. The sequence-specific safety counts do not resolve these questions for the efficacy outcomes.

These gaps constrain interpretation because a crossover comparison depends on having interpretable measurements across the relevant periods, and choices about incomplete records can affect the analyzed population. The posted information does not permit an assessment of the extent or consequences of missing outcome data.

11. 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.

Most frequent non-serious adverse event terms

The registry reports zero serious adverse events among the participants who received the Tempur-Pedic mattress first and zero among those who received the control mattress first. It reports one other adverse event in the Tempur-Pedic-first group and zero in the control-first group. The listed at-risk counts are 5 and 7, respectively. These are the figures recorded for the sequence groups, not a comparison adjusted for exposure time or crossover treatment periods.

In general, a count of zero reported events does not establish that an intervention is risk-free. It means no event of that category is recorded in that group in the registry entry. Small group counts also provide limited information about uncommon events. The record does not report event descriptions, severity details for the other event, attribution, timing, or whether the event occurred during a particular mattress period.

Because participants crossed over between mattresses, sequence-group safety counts should not automatically be read as counts attributable to only one mattress. The registry’s group labels refer to which mattress was received first, and the entry does not provide mattress-period-specific event counts. The adverse-event figures are descriptive registry entries, not evidence that either mattress caused or prevented an event.

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

The study addresses a specific question: how women diagnosed with fibromyalgia and without a sleep disorder rated two mattress types after using each. Its randomized crossover design and stated measurement approach provide context for the question. The record describes mattress preference as the primary outcome and includes sleep monitoring and symptom assessment as additional study elements.

However, the registry record does not report the primary outcome result. It gives no preference percentage, comparative estimate, confidence interval, or p-value. It also does not post numerical findings for PSG measures or symptom severity. As a result, the posted information does not establish which mattress participants preferred, how large any difference was, or how precisely an effect was estimated.

In general, even a reported difference would need to be interpreted alongside uncertainty, the crossover analysis, outcome completeness, and the study’s limitations. A preference ranking is not interchangeable with an objective sleep measure or a symptom change. Likewise, the description of an assessment method is not a result. The registry entry’s mention of chi-squared and t-test methods does not reveal the direction, size, or statistical uncertainty of symptom findings.

The safety entries report no serious adverse events in either sequence group and one other event in the Tempur-Pedic-first group, with none in the control-first group. These descriptive counts do not establish causation, and the record does not assign events to individual mattress periods.

Accordingly, the appropriate reading is limited: the registry documents a completed study with a randomized crossover design and a stated preference endpoint, but its posted results do not provide the outcome values needed to judge the comparative findings. No conclusion about benefit, lack of benefit, or clinical importance can be drawn from the missing primary result.

13. Why This Trial Matters Statistically

This trial is statistically interesting because it uses a crossover design for a comparison in which participants can experience both mattress types. In general, a within-participant design can reduce the influence of stable differences between participants, since each person contributes observations under more than one condition. That advantage depends on suitable measurement in each period and an analysis that recognizes the repeated observations.

The design also makes sequence and time important. Participants received either the Tempur-Pedic mattress first or the control mattress first. If sleep or symptoms change over time, or if experience with the first mattress affects ratings of the second, a treatment comparison can be entangled with period or order effects. The registry record does not report how these issues were evaluated. This highlights why a design label alone is not enough to assess the validity of a treatment contrast.

The primary endpoint combines a practical participant judgment—preference—with descriptions of sleep and symptom assessment. Those outcomes answer related but distinct questions. A preference measure can capture an overall experience, while PSG and symptom measures offer other perspectives. Their interpretation depends on clear definitions, reported estimates, and uncertainty, none of which are posted for the primary result.

The entry also illustrates the difference between a completed study and a fully interpretable record. Completion status and descriptions of methods do not supply the effect estimate. Without numerical primary results, readers cannot assess magnitude or precision, regardless of whether the planned assessments took place. The missing outcome reporting is therefore central to understanding what can and cannot be learned statistically from this record.

14. 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 primary limitation for interpreting this specific study is that the registry record does not report the numerical result for mattress preference, despite identifying it as the primary outcome. It also does not post numerical PSG or symptom findings. There is consequently no effect estimate or uncertainty interval with which to judge the study’s findings.

The registry describes a crossover structure but does not report the sequence-generation method, allocation concealment, washout arrangements, or how treatment, period, and sequence were handled in analysis. It lists quadruple masking without explaining which roles were masked or how masking was maintained. These missing details limit assessment of possible order, measurement, and expectation effects.

Further limitations include the absence of a reported sample-size justification, protocol, detailed analysis plan, multiplicity strategy, and missing-data approach. The registry does not specify the analysis population or explain how incomplete periods or missing ratings would be treated. It also does not provide detailed definitions for the symptom and PSG measures.

The adverse-event information is limited to sequence-group counts, with no event descriptions or mattress-period-specific attribution. Finally, enrollment is recorded as 12, and the record does not provide enough outcome information to assess precision. These are limits of what the registry entry documents; they should not be taken as proof that procedures or analyses were absent from the study itself.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study of Mattress Type in Fibromyalgia — NCT01108718.
• Registry record last updated 2017-03-10; status last verified 2017-01.
• Results first posted 2013-05-31.
• 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.

18. Record Summary

NCT01108718 is a completed, randomized, quadruple-masked crossover study sponsored by Beth Israel Medical Center. Enrollment is recorded as 12. The study began in 2009-07, with primary completion in 2010-10. It compared a Tempur-Pedic mattress and a control mattress, each used for 2 months, in female subjects aged 18 years or older who had fibromyalgia and did not possess a sleep disorder.

The primary outcome is mattress preference, expressed as a percentage of study participants, with a 6 months timeframe. The record describes participant ratings, PSG sleep monitoring, and symptom assessment using chi-squared and t-test methods. It does not report the primary outcome result or numerical findings for sleep or symptoms. Serious adverse events are recorded as zero in both sequence groups; other adverse events are recorded as one in the Tempur-Pedic-first group and zero in the control-first group. The available registry information supports a description of the study, but not a quantitative conclusion about its comparative outcomes.