Higher Water Intake Predicts Very Slightly Higher Time In Bed for Population

Higher Water Intake Predicts Very Slightly Higher Time In Bed for Population

Contents

Variables

A
Water 228
A
Time in Bed 980

Categories

A
Foods 13415
A
Sleep 111

Tags

High Confidence
Very Weak Effect Size
Positive Relationship
Population Study
cause image gauge image effect image
Participants reported a 11.6% average increase in Time In Bed following above average Water Intake.

Abstract

Time In Bed was generally 171% higher than average after a total of 1600 milliliters of Water over the previous 14 days.

Aggregated data from 33 study participants suggests with a HIGH degree of confidence (p=0.181, 95% CI -56.672 to 56.827) that Water has a very weakly positive predictive relationship (R=0.0773) with Time In Bed.

The highest quartile of Time In Bed measurements were observed following an average 201 milliliters Water per day.

The lowest quartile of Time In Bed measurements were observed following an average 4090 milliliters of Water per day.

After an onset delay of 30 minutes, Time In Bed is typically 6% lower than average over the 14 days following around 4090 milliliters of Water Water.

Keywords: Water, Time In Bed, N-of-1 trials, real-world evidence, causal inference, observational study

High Confidence: With 33 participants, these findings have strong statistical power.

Results

Primary Findings

Analysis of 15,673 paired observations from 33 participants revealed a substantial improvement in Time In Bed following above-average Water exposure.

+427.8%
Change from Baseline
Substantial effect on Time In Bed
0.04
Predictor Impact Score
Insufficient evidence for causal relationship

Supporting Statistics

High
Confidence
0.077
Correlation (r)
p = 0.434
Significance
z = 0.69
Effect Magnitude
φ = 1.00
Temporality

What This Means

When participants had above-average Water:

  • Time In Bed increased by 427.8% on average
  • Temporal analysis supports Water as the predictor (not the outcome)

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.

Optimal Daily Values (Precision Dosing)

Based on the observed relationship, we can estimate the predictor values associated with the best and worst outcomes. These values enable personalized dosing recommendations.

ℹ️ Moderate Confidence: Based on 33 participants. Values are reasonably reliable but may refine with additional data.

1,597.8 mL
Value Predicting Higher Time In Bed
Average Water when Time In Bed exceeded its mean
634.1 mL
Value Predicting Lower Time In Bed
Average Water when Time In Bed was below its mean

What This Suggests

Time In Bed tended to be highest when Water was around 1,597.8 mL.

Important: These values reflect correlations, not guaranteed causal effects. Individual responses may vary. Use as a starting point for personal experimentation, not as a definitive prescription. Consult healthcare providers before making treatment decisions.

Population Correlation

Water Distribution

Time In Bed Distribution

Relationship Analysis

Statistical Summary

Relationship Statistics

Property Value
Cause Variable Name Water Intake
Effect Variable Name Time In Bed
Sinn Predictive Coefficient 0.037224464236636
Confidence Level HIGH
Confidence Interval 56.749349320615
Forward Pearson Predictive Coefficient 0.0773
Critical T Value 1.6797878787879
Total Water Intake Over Previous 14 days Before ABOVE Average Time In Bed 201 milliliters
Total Water Intake Over Previous 14 days Before BELOW Average Time In Bed 4090 milliliters
Duration of Action 14 days
Effect Size very weakly positive
Number of Paired Measurements 15673
Optimal Pearson Product 0.092154030503249
P Value 0.18104547236464
Statistical Significance 0.434
Strength of Relationship 56.749349320615
Study Type population
Analysis Performed At 2026-01-04
Number of Participants 33

Water Info

Property Value
Variable Name Water (mL)
Aggregation Method SUM
Analysis Performed At 2020-10-11
Duration of Action 14 days
Filling Value 0
Kurtosis 168.9035754896
Maximum Allowed Value 5000 milliliters
Mean 291.96324979639 milliliters
Median 234.04866468843 milliliters
Minimum Allowed Value 0 milliliters
Number of Aggregate Predictors 0
Number of Aggregate Outcomes 228
Number of Measurements 58290
Number of Measurements (including those generated by tagged, joined, or child variables) 5630
Public true
Onset Delay 30 minutes
Standard Deviation 222.15818986681
Unit Milliliters
User Variables 656
UPC 075720004096
Variable Category Foods
Variable ID 109592
Variance 256166.90856561

Time in Bed Info

Property Value
Variable Name Time In Bed
Aggregation Method MEAN
Analysis Performed At 2020-09-15
Duration of Action 7 days
Kurtosis 37.830671319805
Maximum Allowed Value 7 days
Mean 5 hours
Median 5 hours
Minimum Allowed Value 60 seconds
Number of Aggregate Predictors 859
Number of Aggregate Outcomes 121
Number of Measurements 44465
Number of Measurements (including those generated by tagged, joined, or child variables) 19526
Public true
Onset Delay 0 seconds
Standard Deviation 113.64167274949
Unit Minutes
User Variables 84
UPC 0
Variable Category Sleep
Variable ID 5872231
Variance 18901.026652412

Introduction

Background

Water (Foods) and Time In Bed (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 Water affect Time In Bed?

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 Water for maximizing Time In Bed?

Study Objective

The objective of this study is to determine the nature of the relationship (if any) between Water and Time In Bed. Additionally, we attempt to determine the Water (mL) values most likely to produce optimal Time In Bed 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 427.8% improvement in Time In Bed following above-average Water exposure. The Predictor Impact Score (PIS) of 0.04 indicates insufficient evidence for a causal relationship.

Statistical Significance

Using a two-tailed t-test with alpha = 0.05, it was determined that the change in Time In Bed is statistically significant at a 95% confidence interval. The p-value of 0.4340 indicates there is less than a 43.40% probability that this result occurred by chance.

After treatment, a 11.6% increase (62 minutes) from the mean baseline 6 hours was observed. The relative standard deviation at baseline was 90.5848%. The observed change was 0.693461 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: 3.000
Critical t-value: 1.680

Since t = 3.00 > 1.68, 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 Water might influence Time In Bed.

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 Water 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 Water
  • Confirmation through prospective or randomized designs
  • Biological mechanisms underlying the observed effects

Conclusion

Above-average Water was associated with a 427.8% improvement in Time In Bed—a substantial effect. The Predictor Impact Score of 0.04 indicates this relationship is requiring additional data before conclusions.

Bottom Line: Based on a PIS of 0.04 and a 427.8% effect size, this relationship currently lacks sufficient evidence. Continue monitoring as more data becomes available.

These findings contribute to our understanding of how Water may influence Time In Bed in real-world conditions. While preliminary, these results may inform future research directions.

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Methods

Study Design

This study is based on data donated by 33 participants. Thus, the study design is equivalent to the aggregation of 33 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 30 minutes would pass before a change in Water would produce an observable change in Time In Bed.
  • Duration of Action: It was assumed that Water could produce an observable change in Time In Bed for as much as 14 days after the stimulus event.

Statistical Methods

For each participant, we calculated the Pearson correlation coefficient between Water values and subsequent Time In Bed 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

Water data was primarily collected using Fitbit. Fitbit makes activity tracking easy and automatic.

Time In Bed 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 Water (mL) Affect Time In Bed?. The Journal of Citizen Science. https://studies.crowdsourcingcures.org/study/cause-109592-effect-5872231-population-study
BibTeX 
@misc{sinn_cause_109592_effect_5872231_population_study_2026,
  author = {Sinn, Mike P.},
  title = {Causal Analysis: Does Water (mL) Affect Time In Bed?},
  year = {2026},
  publisher = {The Journal of Citizen Science},
  url = {https://studies.crowdsourcingcures.org/study/cause-109592-effect-5872231-population-study},
  note = {Accessed: January 10, 2026}
}
Chicago/Turabian
Sinn, Mike P. "Causal Analysis: Does Water (mL) Affect Time In Bed?." The Journal of Citizen Science. Accessed January 10, 2026. https://studies.crowdsourcingcures.org/study/cause-109592-effect-5872231-population-study.
Harvard
Sinn, M.P., 2026. Causal Analysis: Does Water (mL) Affect Time In Bed?. [Aggregated N-of-1 Study] The Journal of Citizen Science. Available at: https://studies.crowdsourcingcures.org/study/cause-109592-effect-5872231-population-study [Accessed January 10, 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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