Mediation Techniques for Discrete Dependent and Independent Variables
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Transcript of Mediation Techniques for Discrete Dependent and Independent Variables
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Association Between Insufficient Sleep, Health-Related Quality of Life, and Life
Satisfaction, Among Adults with Asthma: A Mediation Model Approach.
Lauren N. Drinkard, BGS , AACandidate for MPH in Biostatistics, College of
Public Health, Kent, Ohio
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Introduction: Prevalence of Asthma
Shiller, JS, et al. (2010); http://www.cdc.gov/asthma/
Asthma is a chronic respiratory disease
Prevalent in 8% of the U.S. adult population
1 in 12
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Introduction: Public Health Burden of Asthma
http://aafa.org; National Heart Lung and Blood Institute, 2009; Ampon, 2005
Burdens on individuals, workplace, and society
High healthcare costs (20B)Lost work productivity
Healthy People 2020
How does asthma impact individuals?
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Introduction: General Public and Life Satisfaction
U.S. Department of Health and Human Services.; Ampon, R., et al. 2005, Wilson, 1995, Gorman, 2009
Life satisfaction (LS)Insufficient Sleep (IS)Health related quality of life
(HRQOL)
IS LS
HRQOL
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Study Rationale
Gorman, 2009; Carlton, 2005; Guney, 2010; Fagerstrom, 2011; Zullig, 2004; Strine, 2008
Asthmatic adults = sleep abnormalities
Insufficient sleep HRQOL
Insufficient sleep reduced life satisfaction
HRQOL reduced life satisfaction
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Purpose & Objective
Zullig, 2004; Strine, 2008; Colas, 2011; Trojan, 2012
The purpose of this research was to examine the effect of insufficient sleep on life satisfaction in adults with asthma and to determine if HRQOL indicators mediate the effect.
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BRFSS 2010 Total Subjects N = 451,075
Have you ever been told you had asthma? If yes, do you still have asthma?
n = 41,518
Are you pregnant?n = 270
Missing data on predictor, mediators, or outcome
n = 4,586
*n = 36,662 *Subjects in the final sample size could be missing observations on one or more of the covariates
Figure I. Diagram of Sample Size
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Methods: Definitions
Outcome: Life SatisfactionSatisfied (very satisfied/satisfied) Dissatisfied (very dissatisfied/dissatisfied)
Exposure: Insufficient Sleep0-13 days and 14-30 days
Mediators: HRQOLPhysical Health, Mental Health, Overall Physical Health
• 0-13 days and 14-30 daysGeneral Health
• Good (excellent/very good/good)• Not Good (fair/poor)
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Methods: Covariates
Healthcare insurance status
Ability limitation due to health problems
Health problems requiring special equipment
Number of comorbid conditions
Demographics
Socioeconomic Status
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Statistical Analysis
Weighted prevalence estimates: Insufficient sleepHRQOLLife satisfactionCovariates
Logistic regression models were used to study the effect of insufficient sleep on life satisfaction that is mediated through HRQOL indicators
SAS V9.2
MacKinnon, 1993; Barron and Kenny, 1986; Preacher, 2004
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Results: Table I Characteristics
n n n
Age, m (SD)
18-99 years old 36446 46.23 (45.85 - 46.61) 32791 46.28 (45.88 - 46.68) 3655 45.74 (44.65 - 46.84)
Gender, n (%)
Male 9882 36.72 (35.63 - 37.10) 8941 36.64 (35.50 - 37.79) 941 37.39 (33.91 - 40.88)
Female 26780 63.28 (62.20 - 64.37) 24047 63.36 (62.21 - 64.50) 2733 62.61 (59.12 - 66.09)
Race, n (%)
White (Non-Hispanic) 28265 69.37 (68.32 - 70.41) 25538 69.61 (68.51 - 70.71) 2727 67.17 (63.90 - 70.43)
Black (Non-Hispanic) 3362 11.45 (10.73 - 12.16) 2995 11.41 (10.65 - 12.17) 367 11.78 (9.82 - 13.75)
Other (Non-Hispanic) 1365 4.21 (3.73 - 4.68) 1214 4.16 (3.65 - 4.66) 151 4.66 (3.15 - 6.16)
Multi-Racia l (Non-Hispanic) 1034 2.82 (2.49 - 3.15) 895 2.66 (2.33 - 2.99) 139 4.29 (2.90 - 5.68)
Hispanic 2233 11.26 (10.45 - 12.07) 1988 11.26 (10.41 - 12.11) 245 11.25 (8.60 - 13.89)Number of Chronic Conditi ons (CVD, CHD, Stroke, Diabetes ), n (%)
0 26108 78.97 (78.22 - 79.71) 23924 80.21 (79.45 - 80.98) 2184 67.57 (64.72 - 70.41)
1 6855 14.23 (13.59 - 14.87) 5962 13.69 (13.02 - 14.36) 893 19.18 (17.01 - 21.36)
2+ 3699 3.80 (6.39 - 7.21) 3102 6.10 (5.70 - 6.49) 597 13.25 (11.21 - 15.29)
Table I . Socioeconomic Characteristics of Asthmatic Study Participants by Li fe Satisfaction (n = 36,662)
Overall Very Satisfied/Satisfied Dissatisfied/Very DissatisfiedUnadjusted Weighted
Proportion, % Estimate (95% CI)
Unadjusted Weighted Proportion, % Estimate
(95% CI)
Unadjusted Weighted Proportion, % Estimate
(95% CI)
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X (Insufficient Sleep) Y (Life Satisfaction)
Mediators (HRQOL)Mental Health
a b
direct effect: c’
indirect effect: a*b
Mediation Model Approach
total effect: c
X (Insufficient Sleep) Y (Life Satisfaction)
𝑌=𝛽0+𝑐′ 𝑋+𝑏𝑀+𝑍+𝑒
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Standardized Total Effect
= c total effect
Std(c) =
total effect = c = 0.2433
X (Insufficient Sleep) Y (Life Satisfaction)
c ∗ sd(𝑋)ඥσ2(Y′)
where, σ2(Y’) = c2σ2X + 3.4971 = [(0.944*0.944)0.2324]+
0.2433 =
c
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Standardized Direct effect
= 0.6340
Std(c’) =
where, σ2(Y*) = c’2σ2X + b2σ2M + 2cov(X,M) +
X (Insufficient Sleep) Y (Life Satisfaction)
Mediators (HRQOL)Mental Health
c’
c′ ∗ sd(𝑋)ඥσ2(Y∗) 0.1551 =
3.8795 = [(0.6340*0.6340)0.2324]+[(1.5440*1.5440)]+2(0.1582) +
direct effect = c’ = 0.1551
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Standardized Indirect effect
Std(b) =
where, σ2(Y*) = c’2σ2X + b2σ2M + 2cov(X,M) + σ2(Y*) = 3.8795
Std(a)=
where σ2(M’) = α2σ2X +
X (Insufficient Sleep) Y (Life Satisfaction)
Mediators (HRQOL)Mental Health
a b
0.2882 =
b ∗ sd(𝑀)ඥσ2(Y∗)
α ∗ sd(𝑋)ඥσ2(M′)
3.5882 = [(1.1327*1.1327)0.2324]+
0.3119 =
= 1.5440 a = 1.1327
indirect effect: a*b = 0.0899
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Estimate the Proportion Mediated
Proportion of total effect mediated by HRQOL Mental HealthIndirect effect/Total effect
Std a*Std b /Std c
36.95% = 0.0899/0.2433
37% of the effect of insufficient sleep on life satisfaction was mediated by the HRQOL indicator mental health.
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Results of Proportion Mediated
X (Insufficient Sleep) Y (Life Satisfaction)
Mediators (HRQOL)Mental Health: 36.9%
Overall Poor Health: 22.2% General Health: 16.1% Physical Health: 11.7%
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Limitations and Strengths
LimitationsNot able to account for
the severity of asthma
No temporality, so unable to show causation
StrengthsTo our knowledge, first
study to measure the magnitude of the mediated effect of HRQOL among asthmatic adults
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Discussion
Gorman, 2009; ; Guney, 2010; Trojan, 2012; Fagerstrom, 2011 CDCd; Carlton, 2005’ Zullig, 2004; Strine, 2008
Internal consistency of results
External consistency support by previous research
Practicality of findings and impact for asthmatics
Unanswered questions
HRQOL mediates the association between IS LS
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Conclusion
Cross-sectional study suggests strong association between insufficient sleep, HRQOL, and overall life satisfaction
Provides new evidence that HRQOL mediates the relationship between IS LS
Public health practitioners should be aware of sleep quantity and quality as they have implications for health outcomes in adults with asthma.
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Acknowledgments
Dr. Cheruvu
Kent State University College of Public Health
2010 BRFSS study participants
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QUESTIONS?
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