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Multivariate Survival Analysis

John McGready Johns Hopkins University

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Example

“Impact of socioeconomic status on survival with AIDS”   American Journal of Epidemiology,

Volume 148, No. 3 (1998)

4 Continued

Methods

Statistics   Median length of survival and cumulative

probability of survival after an AIDS diagnosis were calculated using the Kaplan-Meier product limit method

  Differences in survival period according to socioeconomic status were analyzed using log-rank

5

Methods

Statistics   Proportional hazards (Cox) regression was used to

assess the association between survival and socioeconomic status after adjustment for potential intervening variables

  All covariates were entered simultaneously into the multivariable model

6 Continued

Results

7

Results

Continued

8

Results

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Example: Cox Proportional Hazards Model

“Donation of blood is associated with risk of myocardial infarction”

  American Journal of Epidemiology, Volume 148, No. 5, 1998

10 Continued

Blood Donation Example

“Because high body iron stores have been suggested as a risk factor for acute myocardial infarction, a donation of blood could theoretically reduce the risk by lowering blood iron stores . . .”

11 Continued

Blood Donation Example

“A cohort of 2,862 men aged 42–60 years were followed for an average of almost nine years”

“One man (0.7%) out of 153 men who had donated blood in 24 months preceding the baseline examination experienced an acute myocardial infarction during 1984–1985. . . .”

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Blood Donation Example

“. . . whereas 316 men (12.5%) of 2,529 non-blood donors had an acute myocardial infarction (p < .0001 for difference in proportions)”

13

Results

Continued

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Results

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Conclusions

“These results indicate that frequent blood loss through voluntary blood donation may be associated with reduced risk of acute MI in middle-aged men”

16 Continued

Issues in Interpreting Results

This was an observational study NOT a randomized trial

Seems likely that blood donors are different than non-donors

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Issues in Interpreting Results

Can we be sure we adjusted for all covariates?

18 Continued

Smoking and Asthma

“Predictors of cigarette smoking and smoking cessation among adults with asthma”

  American Journal of Public Health, Volume 90, No. 48, 2000

19 Continued

Smoking and Asthma

“Remarkably, up to half of U.S. adults with asthma have regularly smoked cigarettes”

“Despite this high lifetime prevalence, the factors predisposing asthmatic persons to initiate smoking are not well understood”

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Smoking and Asthma

“Furthermore, the predictors of smoking cessation, which is a clear priority in adults with asthma, have not been previously examined”

21

Methods

“In the stratum of ever smoking subjects, we constructed a Kaplan-Meier curve to illustrate time until smoking cessation”

“We use Cox PH regression to determine the independent predictors of time until smoking cessation”

22

Subject Characteristics Table, Part 1

23 Continued

Subject Characteristics Table, Part 2

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Subject Characteristics Table, Part 2

25 Continued

Results

“In comparison with college or graduate-level attainment, completion of less than 12th grade was related to a longer period until smoking cessation”

“Age at smoking initiation also predicted smoking cessation, with younger initiation (13 years or younger) associated with longer time until cessation”

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Results

“These con"dence intervals, however, did not exclude the possibility of no effect”

“Daily cigarette consumption of more than one-half pack was also related to a longer period until smoking cessation”

“Conversely, in comparison with early childhood onset of asthma symptoms, onset in late childhood or adolescence was associated with more rapid quitting”

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Conclusions

“Because cigarette smoking is common in people with asthma, smoking prevention and cessation should be priorities in clinical asthma care”

“Asthmatic adults with early childhood asthma onset, early smoking initiation, or heavy daily cigarette consumption may require intensive smoking cessation interventions”

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