Higher Headache Severity Predicts Moderately Higher Sleep Efficiency From Fitbit for Population

Higher Headache Severity Predicts Moderately Higher Sleep Efficiency From Fitbit for Population

Contents

Variables

A
Headache Severity 1498
A
Sleep Efficiency From Fitbit 195

Categories

A
Symptoms 13336
A
Sleep 111

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High Confidence
Weak Effect Size
Positive Relationship
Population Study
cause image gauge image effect image
Participants reported a 6.1% average increase in Sleep Efficiency From Fitbit following above average Headache Severity.

Abstract

Sleep Efficiency From Fitbit was generally 29% higher than average after an average of 1.33 out of 5 of Headache Severity over the previous 24 hours.

Aggregated data from 1 study participants suggests with a HIGH degree of confidence (p=0.001, 95% CI -2.674 to 3.332) that Headache Severity has a moderately positive predictive relationship (R=0.329) with Sleep Efficiency From Fitbit.

The highest quartile of Sleep Efficiency From Fitbit measurements were observed following an average 1.1 out of 5 Headache Severity.

The lowest quartile of Sleep Efficiency From Fitbit measurements were observed following an average 1 out of 5 of Headache Severity.

After an onset delay of 0 seconds, Sleep Efficiency From Fitbit is typically 2% lower than average over the 24 hours following around 1 out of 5 of Headache Severity Headache Severity.

Keywords: Headache Severity, Sleep Efficiency From Fitbit, N-of-1 trials, real-world evidence, causal inference, observational study

Preliminary: Based on 1 participants. Results may change as more data is collected.

Results

Primary Findings

Analysis of 11 paired observations from 1 participants revealed a modest improvement in Sleep Efficiency From Fitbit following above-average Headache Severity exposure.

+5.8%
Change from Baseline
Modest effect on Sleep Efficiency From Fitbit
0.02
Predictor Impact Score
Insufficient evidence for causal relationship

Supporting Statistics

High
Confidence
0.329
Correlation (r)
p = 0.007
Significance
z = 1.09
Effect Magnitude
φ = 1.00
Temporality

What This Means

When participants had above-average Headache Severity:

  • Sleep Efficiency From Fitbit increased by 5.8% on average
  • Temporal analysis supports Headache Severity as the predictor (not the outcome)
  • This relationship is statistically significant (p = 0.007)

Interpreting the Predictor Impact Score

The Predictor Impact Score (PIS) integrates multiple Bradford Hill causal criteria into a single metric. Use this guide to interpret the score:

PIS Range Interpretation Recommended Action
≥ 0.5 Strong evidence High priority for RCT validation
0.3 - 0.5 Moderate evidence Consider for experimental investigation
0.1 - 0.3 Weak evidence Monitor for additional data
< 0.1 Insufficient evidence Low priority; may be noise

Note: PIS is a prioritization heuristic, not proof of causation. High scores indicate relationships worth investigating, not confirmed causal effects. With only 1 participants, these scores are preliminary and will become more reliable as additional data is collected.

Optimal Daily Values

No clear dose-response relationship detected. The Headache Severity values associated with high and low Sleep Efficiency From Fitbit are too similar to provide meaningful dosing guidance. This may indicate a threshold effect (any amount works equally well), no effect, or insufficient data variance. With more participants, a clearer pattern may emerge.

Population Correlation

Headache Severity Distribution

Sleep Efficiency From Fitbit Distribution

Relationship Analysis

Statistical Summary

Relationship Statistics

Property Value
Cause Variable Name Headache Severity
Effect Variable Name Sleep Efficiency From Fitbit
Sinn Predictive Coefficient 0.015663760970861
Confidence Level HIGH
Confidence Interval 3.0028967229808
Forward Pearson Predictive Coefficient 0.3292
Critical T Value 1.796
Average Headache Severity Over Previous 24 hours Before ABOVE Average Sleep Efficiency From Fitbit 1.1 out of 5
Average Headache Severity Over Previous 24 hours Before BELOW Average Sleep Efficiency From Fitbit 1 out of 5
Duration of Action 24 hours
Effect Size moderately positive
Number of Paired Measurements 11
Optimal Pearson Product 0.21837025211852
P Value 0.001
Statistical Significance 0.0074
Strength of Relationship 3.0028967229808
Study Type population
Analysis Performed At 2026-01-04
Number of Participants 1

Headache Severity Info

Property Value
Variable Name Headache Severity
Aggregation Method MEAN
Analysis Performed At 2021-04-22
Duration of Action 24 hours
Kurtosis 2.6188505753424
Maximum Allowed Value 5 out of 5
Mean 2.7185156626506 out of 5
Median 2.6872903614458 out of 5
Minimum Allowed Value 1 out of 5
Number of Aggregate Predictors 1317
Number of Aggregate Outcomes 181
Number of Measurements 5408
Number of Measurements (including those generated by tagged, joined, or child variables) 5408
Public true
Onset Delay 0 seconds
Standard Deviation 0.41171668487351
Unit 1 to 5 Rating
User Variables 351
UPC 0
Variable Category Symptoms
Variable ID 87323
Variance 0.48864093917025

Sleep Efficiency From Fitbit Info

Property Value
Variable Name Sleep Efficiency From Fitbit
Aggregation Method MEAN
Analysis Performed At 2020-09-23
Duration of Action 24 hours
Kurtosis 24.227663163315
Mean 26.276693513514 percent
Median 23.27027027027 percent
Minimum Allowed Value 1 percent
Number of Aggregate Predictors 176
Number of Aggregate Outcomes 19
Number of Measurements 34624
Number of Measurements (including those generated by tagged, joined, or child variables) 3894
Public true
Onset Delay 0 seconds
Standard Deviation 18.585603366682
Unit Percent
User Variables 37
Variable Category Sleep
Variable ID 6057041
Variance 585.5176254255

Introduction

Background

Headache Severity (Symptoms) and Sleep Efficiency From Fitbit (Sleep) are both important factors in understanding human health and well-being. This study investigates the relationship between these two variables using real-world observational data.

Traditional randomized controlled trials (RCTs), while the gold standard for causal inference, are often impractical, expensive, or unethical for studying many health relationships. Aggregated N-of-1 observational studies offer a complementary approach that leverages within-subject comparisons across large populations to identify meaningful patterns.

Research Question

Does Headache Severity affect Sleep Efficiency From Fitbit?

Additionally, we seek to determine:

  1. What is the direction and magnitude of any effect?
  2. How confident can we be in this relationship based on the available data?
  3. What are the optimal levels of Headache Severity for maximizing Sleep Efficiency From Fitbit?

Study Objective

The objective of this study is to determine the nature of the relationship (if any) between Headache Severity and Sleep Efficiency From Fitbit. Additionally, we attempt to determine the Headache Severity values most likely to produce optimal Sleep Efficiency From Fitbit values.

Study Overview

This is a population-level observational study using aggregated N-of-1 methodology. By aggregating individual N-of-1 experiments, we can identify population-level patterns while accounting for the substantial individual variation that exists in most health relationships. Effect sizes are reported as percent change from baseline, enabling intuitive interpretation and comparison across different measures.

Full Methodology: Framework for Real-World Evidence-Based Pharmacovigilance: Aggregated N-of-1 Trials for Quantifying Treatment Effects

Discussion

Interpretation of Findings

Participants experienced a 5.8% improvement in Sleep Efficiency From Fitbit following above-average Headache Severity exposure. The Predictor Impact Score (PIS) of 0.02 indicates insufficient evidence for a causal relationship. This finding is statistically significant (p = 0.007).

Statistical Significance

Using a two-tailed t-test with alpha = 0.05, it was determined that the change in Sleep Efficiency From Fitbit is statistically significant at a 95% confidence interval. The p-value of 0.0074 indicates there is less than a 0.74% probability that this result occurred by chance.

After treatment, a 6.1% increase (5.8 percent) from the mean baseline 94.2 percent was observed. The relative standard deviation at baseline was 5.3%. The observed change was 1.09 times the standard deviation.

A common rule of thumb considers a change greater than twice the baseline standard deviation on two separate pre-post experiments may be considered significant. This occurrence would have only a 5% likelihood of resulting from random fluctuation (a p-value < 0.05).

T-Test Details
Observed t-value: 3.469
Critical t-value: 1.796

Since t = 3.47 > 1.80, we reject the null hypothesis.

Biological Plausibility

A plausible bio-chemical mechanism between predictor and outcome is critical for interpreting observational findings. This is where human judgment excels beyond statistical analysis.

Community feedback on the biological plausibility of this relationship is still being collected. Consider the known mechanisms by which Headache Severity might influence Sleep Efficiency From Fitbit.

Bradford Hill Criteria Assessment

The Bradford Hill criteria provide a framework for assessing causality in observational studies. Our methodology operationalizes six of the nine criteria through the Predictor Impact Score (PIS):

Criterion How Addressed Metric
Strength Effect size magnitude Percent change from baseline (Δ%), z-score
Consistency Cross-participant replication Number of users (N), number of pairs (n)
Temporality Predictor precedes outcome Temporality factor (φ), onset delay (δ > 0)
Biological Gradient Dose-response relationship Gradient coefficient (φgradient)
Plausibility Biological mechanism assessment Community votes on mechanism plausibility
Specificity Category appropriateness Interest factor (finterest)

Predictor Impact Score (PIS)

The PIS integrates multiple Bradford Hill criteria into a composite metric quantifying how reliably a predictor affects an outcome. Higher scores indicate stronger evidence:

Population-Level PIS:

$$\text{PIS}_{\text{agg}} = |r_{\text{forward}}| \cdot w \cdot \phi_{\text{users}} \cdot \phi_{\text{pairs}} \cdot \phi_{\text{change}} \cdot \phi_{\text{gradient}}$$

Where φ-factors are saturation functions approaching 1 as evidence accumulates:

  • φusers = 1 - e-N/10 (user saturation)
  • φpairs = 1 - e-n/nsig (pair saturation)
  • φchange = 1 - e-Δspread/Δsig (effect spread saturation)
  • w = weighted average of plausibility votes

Temporality Assessment

We assess evidence for correct causal direction using the temporality factor:

$$\phi_{\text{temporal}} = \frac{|r_{\text{forward}}|}{|r_{\text{forward}}| + |r_{\text{reverse}}|}$$

Values approaching 1 indicate the predictor precedes the outcome (supporting causation); values near 0.5 suggest ambiguous directionality; values near 0 suggest reverse causation or confounding by indication.

Limitations

As with any observational study, correlation does not prove causation. Key limitations include:

  • Unmeasured confounders: Variables not tracked may influence results
  • Self-selection bias: Health trackers may differ from the general population
  • Measurement error: Self-reported data may contain recall bias
  • Confounding by indication: Sicker individuals may use more treatments

However, within-subject comparison and temporal precedence analysis partially mitigate these limitations. If the relationship is merely coincidental, as participants independently modify their Headache Severity values, the observed strength will decline over time. Spurious correlations naturally dissipate as more data is collected.

Future Directions

Future research should examine:

  • Subgroup analyses to identify individual differences in response
  • Potential confounders and mediators of the observed relationship
  • Optimal dosing and timing for Headache Severity
  • Confirmation through prospective or randomized designs
  • Biological mechanisms underlying the observed effects

Conclusion

📊 Preliminary Findings: With 1 participants, these results are based on limited data. Effect sizes and confidence will improve as more participants contribute data. Consider these findings directional rather than definitive.

Above-average Headache Severity was associated with a 5.8% improvement in Sleep Efficiency From Fitbit—a modest effect. The Predictor Impact Score of 0.02 indicates this relationship is requiring additional data before conclusions.

Bottom Line: Based on a PIS of 0.02 and a 5.8% effect size, this relationship currently lacks sufficient evidence. Continue monitoring as more data becomes available. Note: These conclusions may strengthen or change direction as more data is collected.

These findings contribute to our understanding of how Headache Severity may influence Sleep Efficiency From Fitbit in real-world conditions. The within-subject design and temporal analysis provide confidence in these relationships, though observational limitations remain.

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Methods

Study Design

This study is based on data donated by 1 participants. Thus, the study design is equivalent to the aggregation of 1 separate n=1 observational natural experiments.

This within-subject design is powerful because it controls for all stable individual characteristics (genetics, baseline health status, socioeconomic factors) that might otherwise confound the relationship between variables.

Data Analysis

Temporal Assumptions

The analysis incorporates temporal assumptions about the relationship between variables:

  • Onset Delay: It was assumed that 0 seconds would pass before a change in Headache Severity would produce an observable change in Sleep Efficiency From Fitbit.
  • Duration of Action: It was assumed that Headache Severity could produce an observable change in Sleep Efficiency From Fitbit for as much as 24 hours after the stimulus event.

Statistical Methods

For each participant, we calculated the Pearson correlation coefficient between Headache Severity values and subsequent Sleep Efficiency From Fitbit values. Individual correlations were then aggregated using Fisher's z-transformation to produce a population-level estimate:

Individual Correlation:

$$r_i = \frac{\sum(x_{ij} - \bar{x}_i)(y_{ij} - \bar{y}_i)}{\sqrt{\sum(x_{ij} - \bar{x}_i)^2 \sum(y_{ij} - \bar{y}_i)^2}}$$

Fisher's Z-Transformation:

$$z_i = \frac{1}{2} \ln\left(\frac{1 + r_i}{1 - r_i}\right)$$

Aggregated Correlation:

$$\bar{r} = \tanh(\bar{z}) \quad \text{where} \quad \bar{z} = \frac{1}{N}\sum_{i=1}^{N} z_i$$

Effect Size Calculation

Effect sizes are reported as percent change from baseline. For each participant, we compare the outcome following above-average predictor values to the overall baseline outcome:

$$\Delta\%_{\text{baseline}} = \frac{\bar{O}_{\text{follow-up}} - \bar{O}_{\text{baseline}}}{\bar{O}_{\text{baseline}}} \times 100$$

Effect Magnitude (Z-Score)

To assess effect magnitude relative to natural variability, we calculate the z-score:

$$z = \frac{|\Delta\%_{\text{baseline}}|}{\text{RSD}_{\text{baseline}}}$$

where RSDbaseline is the relative standard deviation of outcome during baseline period

A z-score > 2 indicates statistical significance (p < 0.05), meaning the observed change exceeds typical baseline fluctuation and is unlikely due to random variation.

Statistical Significance

Correlation significance is assessed using a two-tailed t-test:

$$t = \frac{r\sqrt{n-2}}{\sqrt{1-r^2}}$$

We reject the null hypothesis (ρ = 0) at α = 0.05 when |t| exceeds the critical value, providing statistical evidence that the observed relationship is not due to chance.

Data Sources

Headache Severity data was primarily collected using QuantiModo. QuantiModo allows you to easily track mood, symptoms, or any outcome you want to optimize in a fraction of a second. You can also import your data from over 30 other apps and devices. QuantiModo then analyzes your data to identify which hidden factors are most likely to be influencing your mood or symptoms.

Sleep Efficiency From Fitbit data was primarily collected using Fitbit. Fitbit makes activity tracking easy and automatic.

Data Quality

Data quality measures were applied to ensure reliable results:

  • Minimum Data Requirement: Only participants with sufficient paired observations were included in the analysis.
  • Outlier Handling: Extreme values were winsorized to reduce the influence of measurement errors.
  • Missing Data: Days with missing values were handled using appropriate filling strategies based on the variable type.
  • Test User Exclusion: Test accounts and invalid users were excluded from all analyses.

Principal Investigator

Program & Methods

Mike P. Sinn
Sinn, M. P.

Designed and implemented data collection, aggregation, causal inference pipeline, and automated study generation framework. Developed the Predictor Impact Score methodology operationalizing Bradford Hill criteria for ranking causal relationships in observational data. When he tells people this at parties, they usually say they have to go check on their car.

Individual study outputs are automated, reproducible, and open to external audit. (Which I would seriously recommend.)

Contact

Cite This Study

APA Format
Sinn, M. P. (2026). Causal Analysis: Does Headache Severity Affect Sleep Efficiency From Fitbit?. The Journal of Citizen Science. https://studies.crowdsourcingcures.org/study/cause-87323-effect-6057041-population-study
BibTeX 
@misc{sinn_cause_87323_effect_6057041_population_study_2026,
  author = {Sinn, Mike P.},
  title = {Causal Analysis: Does Headache Severity Affect Sleep Efficiency From Fitbit?},
  year = {2026},
  publisher = {The Journal of Citizen Science},
  url = {https://studies.crowdsourcingcures.org/study/cause-87323-effect-6057041-population-study},
  note = {Accessed: January 6, 2026}
}
Chicago/Turabian
Sinn, Mike P. "Causal Analysis: Does Headache Severity Affect Sleep Efficiency From Fitbit?." The Journal of Citizen Science. Accessed January 6, 2026. https://studies.crowdsourcingcures.org/study/cause-87323-effect-6057041-population-study.
Harvard
Sinn, M.P., 2026. Causal Analysis: Does Headache Severity Affect Sleep Efficiency From Fitbit?. [Aggregated N-of-1 Study] The Journal of Citizen Science. Available at: https://studies.crowdsourcingcures.org/study/cause-87323-effect-6057041-population-study [Accessed January 6, 2026].

Study Type: Aggregated N-of-1 Observational Mega-Study
Evidence Level: Level II (Real-World Evidence)
Methodology: Bradford Hill Criteria with Predictor Impact Score (PIS)

References

This framework was originally developed in 2013 based on the Bradford Hill criteria. Subsequent literature has independently validated similar approaches to causal inference from observational data:

  1. Hill, A.B. (1965). The environment and disease: association or causation? Proceedings of the Royal Society of Medicine, 58(5), 295-300. [Bradford Hill criteria]
  2. Lillie, E.O., et al. (2011). The n-of-1 clinical trial: the ultimate strategy for individualizing medicine? Personalized Medicine, 8(2), 161-173. [N-of-1 methodology]
  3. Pearl, J. (2009). Causality: Models, Reasoning, and Inference . Cambridge University Press. [Causal inference]
  4. Hernán, M.A., & Robins, J.M. (2020). Causal Inference: What If . Chapman & Hall/CRC. [Free textbook]
  5. FDA (2018). Framework for FDA's Real-World Evidence Program . U.S. Food and Drug Administration. [Regulatory context]
  6. Duan, N., et al. (2013). Single-patient (n-of-1) trials: a pragmatic clinical decision methodology . Journal of Clinical Epidemiology, 66(8), S21-S28.
  7. Platt, R., et al. (2018). The FDA Sentinel Initiative—an evolving national resource . New England Journal of Medicine, 379(22), 2091-2093.

This information is for research and educational purposes only, not medical advice. Consult a healthcare provider before making health decisions. Terms of Service

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