Speaking Notes

PADM 5324

September 8, 2009

Dr. Neubauer

WHERE WE ARE

• Are there any "In the News" reports this evening?
• I am pleased to see that we are beginning to use Google Docs to write the paper together. Please indicate your sources (including sources of images) and write in your own "voice."
• I don't have a homework one assignment ready yet. I will move the due date to Sept. 29. Please refer to course calendar on the course Web site.

CHAPTER 3 of our textbook . . .

1) What is the difference between morbidity and mortality?

2) An incidence rate is usually expressed per ________ people in a population.

3) An indigence rate includes the number of people who already had the disease or condition prior to the period of time the incidence rate is based upon. True or False?

4) There are 3,500 students on a college campus, of which 3,000 are at risk for a particular disease or condition. In CY 2008 there were 500 new instances of the disease/condition among the student body. Calculate the incidence rate for CY 2008, expressed as a rate per 1000.

5) There were 400 people on a cruse ship. One hundred people on a cruise ship ate the potato salad. Of those who ate the potato salad 25 became ill. Assuming the potato salad was the cause of the illness of the 25, calculate the attack rate, expressed as a percent.

http://en.wikipedia.org/wiki/Attack_rate

6) The attack "rate" is not an incidence rate because it is calculated based on those exposed rather than those in the population who would have been at risk if they had been exposed. True or False?

7) When the period of time upon which calculation of an incidence rate is of long duration it is not unusual for some of the persons originally observed to no longer be available for observation. What would be the consequence on the resulting calculated incidence rate to assume that they were still being observed and did not contract the disease/condition for the entire duration of the observation?

7a) Why is it important to calculate an incidence density (rather than an incidence rate) when persons in the relevant population are not available to be observed for the entire duration of the observation?

8) What is the public health word for the means by which a disease proliferates (spreads) through a population?

9) Why might the intensity of surveillance of a population for a particular disease tend to produce an apparent increase in the incidence rate for the disease in that population?

10) Why might the discovery of drugs that enable people to survive with a disease or condition lead to an increase in the observed prevalence of the disease or condition?

CHAPTER 4 OVERVIEW

The annual mortality rate for all causes for a population (expressed per 1,000 people) =

total number of deaths DIVIDED BY

number of persons in the population at midyear

TIMES 1,000

The same calculation can be made for AGE SPECIFIC and CAUSE SPECIFIC interests.

Notice that this is an incidence rate only if everyone in the numerator is at risk of dying from the specified cause.

The CASE-FATALITY RATES can be calculated and represented as a PERCENT using the formula on page 62 of our textbook. Notice that all the people represented by the denominator have (or perhaps have had) the disease.

A measure of PROPORTIONATE MORTALITY can be calculated as a percent (for a period of time) such that the numerator reflects the number of deaths from a particular disease during the period of time and the denominator is the total number of deaths in the population during the period.

A change in the PROPORTIONATE MORTALITY associated with a particular disease can be the result of changes in the number of deaths attributed to other diseases or conditions.

YEARS OF POTENTIAL LIFE LOSS

In one sense, every premature death is equally great loss.

In another sense, the premature death of a younger person is a greater loss than the premature death of an older person. When a younger person dies more expected years of living have been lost. This can be understood in different ways, including economically in terms of one's ability to work, thereby producing value for society.

Attempting to put monetary values on the consequences of premature death is filled with subjective judgments and ethical difficulties. Thankfully, the implications of making such judgments for the sake of creating public policies are beyond the scope of this course. Policy and budgetary decisions may reflect such judgments but probably at a rather subjective level.

According to our textbook, the age 65 is apparently used to determine the years of potential life lost as a result of the death of a person younger than 65.

Current world average lifespan at birth is 65 years of age. This includes infant mortalities. http://en.wikipedia.org/wiki/Life_expectancy

LIFE EXPECTANCY is the average number of years remaining at a given age. That is not the same as the average age at time of death.

QUESTIONS REGARDING CAUSE OF DEATH

Death certificates are maintained by state governments in the United States. I don't think they are entirely standardized.

Things that can affect the information on a death certificate:

• The predispositions of the person completing the report.
• The amount of information available.
• The possible relationship between the person deceased and the person entering the data. (Stranger? Personal physician? Family member?)
• The possible implications for a law suit or insurance settlement.

The example of a death certificate included in our textbook includes . . .

• Immediate cause of death
• Underlying causes
• Other significant medical conditions

I think the point is that when studying mortality in a population it is important to realize that while the fact of death is objective, there can be substantial inconsistency and subjectivity regarding how "cause of death" is identified and officially recorded. This has implications for some public health research.

RELATIONSHIP BETWEEN MORTALITY AND MORBIDITY

For some diseases/conditions, case-based mortality rates are a good indicator of incidences of morbidity. This is the case of the immediate cause of death is almost always fatal within a relatively short time period.

OPTIONAL EXTRA MATERIAL

Could there be a medical cure for aging? Raymond Kurzweil and others believe that that advances in biogenetics and general medical technology could completely cure aging by 2020. See his book titled, The Singularity is Near. While significant human life extension is probably possible, nothing is likely to save us from eventually being "hit by a bus," or a similar fate. However, significant life extension may well cause very important practical and ethical problems for public health professionals and other policy makers, given the constrained capacity of earth to maintain ever-larger human populations.

CHAPTER 5 OVERVIEW

This chapter contains several pairs of related terms. I think the basic point is that community screening and the diagnoses of individual patients involves uncertainty and subjective judgments. One of the major ideas (not included below) is that the interpretation of a finding can be affected by the prevalence of the disease/condition in the population. Without these insights policy makers and others can make inappropriate decisions based on the facts as revealed by scientific means.

• Screening vs. Diagnostic testing
• Sensitivity and Specificity
• http://en.wikipedia.org/wiki/Sensitivity_and_specificity
• False Positives and False Negatives
• Sequential Testing and Simultaneous Testing
• Dichotomous Variables and Continuous Variables
• Intraobserver Variation and Interobserver Variation
• Reliability and Validity

----------------------

Screening vs. Diagnostic testing

In public health screening you are looking for instances of a particular disease/condition among a sample of members of a population.

In diagnostic testing a physician is trying to know what is wrong with a particular patient.

Sensitivity and Specificity

http://en.wikipedia.org/wiki/Sensitivity_and_specificity

• The sensitivity of a test is a measure of the proportion of actual positives which are correctly identified by the test.

• The specificity of a test is a measure of the proportion of the actual negatives which are correctly identified by the test.

• An ideal medical test is 100% sensitive and 100% specific. It is VERY unlikely that any test for a disease or condition is this good.

False Positives and False Negatives

• When a medical test is given it may return a false positive. This means that the test indicates that the patient has the disease/condition when in fact he/she does not.

• When a medical test is given it may return a false negative. This means that the test indicates that the patient does not have the disease/condition when in fact he/she has it.

• There are different consequences of false positives and false negatives.

Sequential Testing and Simultaneous Testing

• Given the uncertainty of the results of any one test it may be advisable (or not, depending of costs and risks associated with the tests themselves) to screen people or diagnosis patients using multiple (different) tests.

• In sequential testing you get back the result of the first test before deciding to do a second (usually different) test.

• In simultaneous testing you give the patient two or more tests at the same time.

• The calculations regarding resulting the resulting sensitivity and specificity of the multiple tests combined differs based on whether the testing was done sequentially or simultaneously.

Dichotomous Variables and Continuous Variables

• Some tests involve measurement of variables that are like a light-switch -- either on or off. Other tests involve measurement of variables like blood pressure -- the range of possible values is continuous.

• The interpretation of the meaning of dichotomous variables is more objective than the interpretation of the meaning of continuous variables.

Intraobserver Variation and Interobserver Variation

• If the same observer looks at the same data twice he/she will not always draw the same conclusion. Hopefully he will usually, "agree with himself."

• If two observers look at the same data (separately) they may or may not draw the same conclusion. Hopefully, they will usually agree with each other.

Reliability and Validity

• A test (or the measurement of a variable) is said to be reliable if repeated applications of the test on the same (unchanged) subject yield the same outcomes.

• A test (or measure) is said to be valid if it in facts measures what it is intended to measure.

• Good tests (and measures) are both reliable and valid.