CHAPTER 16

Life Tables

OUTLINE

 

16.1            GENERAL USE OF LIFE TABLES

Discusses life tables, used by demographers and researchers to describe the mortality or longevity of a population

 

16.2            CURRENT LIFE TABLES

Analyzes a current life table

 

16.3            FOLLOW-UP TABLES

Describes a neat technique for tracking survival of patients with chronic diseases

 

LEARNING OBJECTIVES

•  • 1.                    Distinguish among the three types of life tables

• 2.                    Identify and be able to compute the components of a current life table

• 3.                    Compute measures of mortality and longevity from a life table

• 4.                    Construct a follow-up life table•  

GENERAL USE OF LIFE TABLES

• A.      Used by demographers to measure and analyze the mortality or longevity of a population or one of its segments

• B.       Used by insurance companies to compute premiums

• C.       By research workers to determine whether the differences in mortality or longevity of two groups are significant

• D.      Employed to predict survival or the likelihood of death at any time

• E.       Life table analysis can be fundamental to the solution of many public health and medical problems

• F.       Current life table illustrates how age-specific death rates affect a population

• G.       Cohort Life Table – follows a defined group (a cohort) from birth (or some measurable point in time) until the last person in the group has died – also know as a generation life table)

•  

CURRENT LIFE TABLES

• AGE INTERVAL – • is the period of time between two exact ages stated•  

• AGE-SPECIFIC DEATH RATE – • The numerator for this rate is the average number of deaths per year in a 3-

year period, divided by the July 1 average population for each of the 3 years•  

• CORRECTION TERM () – • defines and adjusts for maldistribution•  

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CURRENT LIFE TABLES

• CORRECTED (ESTIMATED) DEATH RATE –

• denotes the proportion of persons who are alive at the beginning of the age interval but die during that interval

•  

•

•  

• NUMBER LIVING AT BEGINNING OF AGE INTERVAL –

• the number of persons, starting with the original cohort of 100,000 live births, who survive to the exact age marking the beginning of each interval.

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CURRENT LIFE TABLES

• NUMBER DYING DURING AGE INTERVAL – • number of the original 100,000 who die during each successive age interval

– calculated by multiplying the proportion dying during the interval by the number alive at the beginning of the interval

•  ••  • PERSON-YEARS LIVED IN INTERVAL – • totality of years lived by the survivors of the original 100,000 between the

ages x and (x + n)•  •• for all intervals except the last, for which

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CURRENT LIFE TABLES

• EXPECTATION OF LIFE –

• the average number of years of life remaining to those who survive to the beginning of the age interval – calculated by dividing the number of person-years lived after a given age by the number who reached that same age

•  

•

•  

•

• Odds of surviving from birth to age 65

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CURRENT LIFE TABLES

•  • A.      Median age at death – age to which precisely half of the cohort

survives•  •  

• B.      Life span

– 1.                  the age that persons are likely to reach, given optimal conditions

– 2.                  defined as that age reached by the longest-lived 0.1% of the population – currently quite close to 100 years

•  

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FOLLOW-UP TABLES

• A.        Provides a basis for answering the question “how long do I have”

• B.        Often used to evaluate the relative effectiveness of alternative modes of treatment by computing the probability of survival of patients treated using each mode

• C.        Particularly useful because it utilizes the experience of each person for the entire time he or she is in the study; that is, the method considers the period of exposure in terms of person-years or other appropriate units

• D.       Data for life tables identically, provided that

– 1.                    death rates do not change materially over time

– 2.                    exposure to the disease prior to treatment is not increasing with time

•  

CONSTRUCTION OF FOLLOW-UP TABLE

•  • A.        To construct a follow-up table:

– 1.                    you need to know the follow-up period after some event

– 2.                    to ensure accuracy, you need well-defined starting and end points

• B.        Given a know period of observation for each patient, you can then tally

– 1.                    how many survive

– 2.                    how many die

– 3.                    how many are lost to follow-up during the first and subsequent years of the study

CONSTRUCTION OF FOLLOW-UP TABLE

• C.                  Construction of the table

– 1. = total number of patients who begin the study

– 2. = probability of surviving the first year

– 3. = persons lost to follow-up

– 4. = withdrawals from the study alive

– 5. Assumed that and live half way through the interval

•  

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CONSTRUCTION OF FOLLOW-UP TABLE

•   Estimate of surviving the second year of follow-up:•  ••  

• Probabilities of surviving subsequent year are computed similarly

•  ••  • Probability of surviving the first five years is•  

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CONSTRUCTION OF FOLLOW-UP TABLE

• A.      5-year survival rate – commonly used in cancer research as a measure of a treatment’s effectiveness

• B.      Determining statistical significance between , the xth-year survival rate of a treatment group, and , the xth-year survival rate of a control group

•  •  

• where and are standard errors for the two groups and Z is the normal score

•  • Standard error equation

•  

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CONCLUSION

Life tables provide excellent means for measuring mortality and longevity. The current life table shows the effects of age-specific death rates on a group. From this table, measures of mortality and life expectation can be computed. Whereas the current life table presents a hypothetical picture of the effects of present mortality rates, the cohort life table is an actual historical record of the mortality of a group followed through life. The follow-up life table considers the experiences of persons from event to event during the period of a study.

Pareto chart

• Vilfredo Pareto – (Italian economist/sociologist, 1848 - 1923)

• In the real world a minority of causes lead to the majority of problems.

• Ergo: The Pareto Principle• 80/20 Rule

Swift V-12 Sales by Age Group

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Cause and Effect Diagrams Ishikawa

• Sometimes called a “fishbone diagram”• Benefits

– Creating the diagram itself is an enlightened, instructive process.

– Such diagrams focus a group, thereby reducing irrelevant discussion.

– Such diagrams separate causes from symptoms and force the issue of data collection

– Such diagrams can be used with any problem

Fishbone diagram

EFFECT

Cause

Cause Cause

Cause

Cause

Cause

Fishbone diagram

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Fishbone diagram

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Parts

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Flux

Contamination

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vendors

storage

age

Run and Control Charts(Trend chart)

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Steps: Planning a Health Survey

1. Make a written Statement of the purpose

2. Formulate Objectives and Hypotheses

3. Specify the target population

4. List the variables

5. Review existing data

6. Decide how to collect data

7. Establish a time frame

8. Design the questionnaire

9. Pretest the questionnaire

10. Obtain informed consent

11. Select the sample

12. Collect the date

13. Edit and code the data

14. Analyze the data

15. Report the findings