PUBH 401 Quiz 2 and 3 prep

incidence density

Use of a person-time denominator in the calculation of rates; a person-day reflects one person at risk for 1 day, and a person-year represents one person at risk for 1 year

Disease-specific or cause-specific rate is used when the rate is limited to deaths from

a certain disease

Sequential (Two-stage) Testing

a less expensive, less invasive, or less uncomfortable test is generally performed first, and those who screen positive are recalled for further testing with a more expensive, more invasive, or more uncomfortable test, which may have greater sensitivity and specificity

Years of Potential Life Lost (YPLL)

a measure of premature mortality, or early death. YPLL recognizes that death occurring in the same person at a younger age clearly involves a greater loss of future productive years than death occurring at an older age.

Incidence is generally used for __________diseases, prevalence is used for more __________ , conditions or attributes of ill-health

acutely acquired diseases, permanent states

An age restriction on the mortality rate will become an

age-specific mortality rate

Formula to calculate Incidence

# of new cases of a disease occurring in the population during a specified period of time / # of persons at risk of developing the disease during that period time x 1000

Case Fatality Rate Formula

( # of cause-specific deaths among incident cases ) / (# of incident cases ) X 100

Kappa Statistic formula

(Percent agreement observed) - (Percent agreement expected by chance alone) / 100% - (Percent agreement expected by chance alone)

percent agreement formula

(a / a+b+c) x 100

Issues with false positive

1) A burden is placed on the health care system 2) Anxiety and worry are induced in persons who have been told that they have tested positive

YPLL assists in three important public health functions

1) Establishing research and resource priorities 2) Surveillance of temporal trends in premature mortality 3) Evaluating the effectiveness of program interventions

Two conditions must be met in order for mortality to reflect a good incidence rate and the measure of risk of disease.

1) High case-fatality rate 2) Short survival rate

In an Asian country with a population of 6 million people, 60,000 deaths occurred during the year ending December 31, 2010. These included 30,000 deaths from cholera in 100,000 people who were sick with cholera. What was the cause-specific mortality rate from cholera in 2010? _____ 2 What was the case-fatality from cholera in 2010? _____

1. 5/1,000 2. 30%

A prevalence survey conducted from January 1 through December 31, 2012, identified 1,000 cases of schizophrenia in a city of 2 million persons. The incidence rate of schizophrenia in this population is 5/100,000 persons each year. What percentage of the 1,000 cases were newly diagnosed in 2012? ____

10%

Prevalence can never exceed

100%

In 1990, there were 4,500 deaths due to lung diseases in miners aged 20 to 64 years. The expected number of deaths in this occupational group, based on age-specific death rates from lung diseases in all males aged 20 to 64 years, was 1,800 during 1990. What was the standardized mortality ratio (SMR) for lung diseases in miners? ______

2.5 or 250

kappa statistic

A measure of the degree of nonrandom agreement between observers of the same categorical variable.

We wanted to conduct a study to assess alcohol use in college students at a local public university. The sample in our study was selected from a religious-based club on campus. We found that the percent who drank was very low and concluded that students in general drink very little on this campus. Is the conclusion accurate?

Answer - NO

Which of the following statements regarding direct adjustment is TRUE?

For direct age-adjustment, the weight for a given age category is the number of individuals in the standard population for that age group

lead time bias

Bias introduced when screening detects a disease earlier and thus lengthens the time from diagnosis to death.

A program manager from an international health funding agency needs to identify regions that would benefit from an intervention aimed at reducing premature disability. The program manager asks a health care consultant to develop a proposal using an index that would help her make this decision. Which of the following would best serve this purpose?

Disability-adjusted life-years

The following health statistics are available on the Internet for country Z about two disease outcomes. Disease A has an annual incidence of 225 per 100,000 population and an annual mortality rate of 150 per 100,000. Disease B has an annual incidence of 500 per 100,000 population and the same annual mortality rate as disease A. Neither disease A or B has a cure. What would you conclude regarding the burden of these diseases in country Z?

Disease B has a higher prevalence than disease A

positive predictive value

Divide the number of true positives by the total number who tested positive (true positives + false positives).

Age-adjusted death rates are used to

Eliminate the effects of differences in the age distributions of populations in comparing death rates

false negative (FN)

Have disease but have negative test

Disease X has a duration of 15 years and a low incidence (5 per 100,000 person-years). Disease Y has a duration of 5 years and a low incidence (5 per 100,000 person-years). Comparing Disease X to Y in the same population, we would expect Disease X to have a:

Higher prevalence

For a disease such as pancreatic cancer, which is highly fatal and of short duration:

Incidence rates and mortality rates will be similar

At an initial examination in Oxford, Massachusetts, migraine headache was found in 5 of 1,000 men aged 30 to 35 years and in 10 of 1,000 women aged 30 to 35 years. The inference that women have a two times greater risk of developing migraine headache than do men in this age group is:

Incorrect, because no data for a comparison or control group are given

The mortality rate from disease X in city A is 75/100,000 in persons 65 to 69 years old. The mortality rate from the same disease in city B is 150/100,000 in persons 65 to 69 years old. The inference that disease X is two times more prevalent in persons 65 to 69 years old in city B than it is in persons 65 to 69 years old in city A is:

Incorrect, because of failure to distinguish between prevalence and mortality

A survey was conducted among the non-hospitalized adult population of the United States during 2008 through 2011. The results from this survey are shown below. Age Group Persons With Hypertension (%) 18-29 years 4 30-39 years 10 40-49 years 22 50-59 years 43 60-69 years 54 70 and older 64 The researchers stated that there was an age-related increase in the risk of hypertension in this population. You conclude that the researchers' interpretation:

Is incorrect because prevalence is used

Among workers in a fish processing plant, 30% of all deaths were due to myocardial infarction. Among workers in a brewery, 10% of all deaths were due to myocardial infarction. Investigators concluded that workers in the fish processing plant had a greater risk of death due to myocardial infarction than workers in the brewery. This conclusion:

May be incorrect because it is based on proportionate mortality

Which of the following is an advantage of active surveillance?

More accurate due to reduced reporting burden for health care providers

Kaplan-Meier Method

Most common type of survival analysis. Utilizes log-rank test which is most common statistical test for survival time and 2 independent groups.

True Negative (TN)

No disease and have negative test

False Positive (FP)

No disease, but have positive test

Standardized Mortality Ratio (SMR)

Observed # of death per yr / expected # of death per yr

Relative survival rate formula

Observed survival in people with the disease / Expected survival if disease were absent

point prevalence rate

Proportion of individuals in a specified population at risk who have the disease of interest at a given point in time

Formula for specificity

TN/(TN+FP)

Formula for sensitivity

TP/(TP+FN)

Chikungunya virus infection was recently introduced into the Dominican Republic. During the first year after introduction, the virus has infected a total of 251,880 people in the Dominican Republic, which has a population size of 10.4 million people. Infection by the chikungunya virus is rarely fatal. Which of the following is correct?

The 1-year cumulative incidence of chikungunya is 24.2 per 1,000 persons

Surveillance data indicate that the prevalence of chronic liver disease in the United States increased 104% between the years 1990 and 2008. While chronic liver disease occurs in persons of all ages, the highest mortality rate occurs in people 65 years old or older. The United States has proportionately more people 65 years or older than Country X. What would happen if crude mortality rates in the United States were age standardized to the population of Country X in order to compare the risk of dying of chronic liver disease in the two populations?

The age-standardized mortality rate for the United States would be less than the crude mortality rate for the United States

The incidence rate of a disease is five times greater in women than in men, but the prevalence rates show no sex difference. The best explanation is that:

The case-fatality from this disease is greater in women

Cumulative Incidence

The incidence is calculated by using a period of time during which all of the individuals in the population are considered to be at risk for the outcome.

True Positive (TP)

have disease and have positive test

define prevalence

The number or proportion of cases of a particular disease or condition present in a population at a given time.

Proportionate Mortality

The proportion of deaths in a specified population over a period of time attributable to different causes. Each cause is expressed as a percentage of all deaths, and the sum of the causes must add to 100%. These proportions are not mortality rates, since the denominator is all deaths, not the population in which the deaths occurred.

What would be the effect on age-specific incidence rates of uterine cancer if women with hysterectomies were excluded from the denominator of the calculations, assuming that there are some women in each age group who have had hysterectomies?

The rates would tend to increase

Assumptions Made in Using Life Tables

There has been no temporal change in the effectiveness of treatment or in survivorship over calendar time The second assumption relates to follow-up of persons enrolled in the study

Mortality rate calculation

Total number that died in given time period (1yr) / Total population number (use midpoint of time period ) x 1000

A rate ideally is a proportion in which

change over time is considered, but in practice, often used interchangeably with proportion, without reference to time.

Mortality rate

death rate

Morality Data may not be accurate because

differences in how one health care professional may code the underlying cause of death compared with another

Kappa greater than 0.75 represents

excellent agreement

Case-Fatality Rate is

ideally suited to diseases that are short-term, acute conditions

An example of a prevalence rate

if we wanted to calculate cancer prevalence, it would be the number of individuals with cancer at a specified period of time divided by the number of people in the population at a specified period of time

Mortality is clearly an index of the severity of a disease from both clinical and public health standpoints, but mortality can also be used as an

index of the risk of disease

kappa of 0.40 to 0.75 represents

intermediate to good agreement

Validity

its ability to distinguish between who has a disease and who does not

Overall Percent Agreement

measure of the total agreed upon number of observations between two tests/observers out of the total number of observations.

if test results cannot be reproduced, the value and usefulness of the test are

minimal

•One of the most important aspects of the incident rate is that it measures the ________ cases of disease in a population.

new

mortality is not a good index/measure of incidence when a disease is

not fatal

Relative Survival Rate

observed survival in people with disease/expected survival if disease were absent

One problem with using person-years is that each person-year is assumed to be equivalent to every

other person-year (the risk in any person-year observed is the same).

case fatality rate

percentage of population that dies from a specific disease

kappa below 0.40 represents

poor agreement

Time must always be__________ in any mortality rate. It can be calculated over 1 year, 5 years, or longer

precisely specified

Passive Surveillance

reporting often falls on the health care provider, but many don't have time to report diseases and therefore active surveillance is needed.

The incidence rate can tell us the "_______" in a population

risk

if one is calculating the incidence rate for prostate cancer, only men who are at ________ for developing the disease should be included - not women

risk

case-fatality rate is a measure of the

severity of the disease

Mortality rate can be separated by

specific age groups, men or women, specific variable relevant to population

A restriction that is placed on a rate is called a

specific rate

Active Surveillance

staff actively go out to hospitals and physicians and other health care agencies to record any cases of the disease

representative

subjects that are correctly gathered from a population. To show an accurate microcosm of a larger population

Years of Potential Life Lost (YPLL) calculation

subtract each deceased person's age at death from a predetermined age at death. U.S. predetermined "standard" age is 65. For example, if a child dies at age 5, the YPLL is 65 - 5 = 60. Years of potential life lost for each individual are then added together to yield the total YPLL for the specific cause of death

What is surveillance?

surveillance is a continuous and systematic process of collection, analysis, interpretation, and dissemination of descriptive information for monitoring health problems

Specificity

the ability of the test to identify correctly those who do not have the disease

Sensitivity

the ability of the test to identify correctly those who have the disease

Underlying cause

the disease or injury which initiated the train of morbid events leading directly or indirectly to death or the circumstances of the accident or violence which produced the fatal injury

Generalizability

the extent to which we can claim our findings inform us about a group larger than the one we studied

Median Survival Time

the length of time that half of the study population survives

Define morbidity

the number of ill/sick people in the population

case-fatality rate

the number of people who die of a disease divided by the number of people who have the disease

Five-Year Survival Rate

the percentage of patients diagnosed with a certain disease who will be alive five years after the date of diagnosis; used to estimate the prognosis of a particular disease

Person-year

the unit used for counting observation time in a study because individuals are often observed for different periods of time

The other important concept for the denominator is that it includes _______.

time

Interobserver variation

variation between those reading the test results

intraobserver variation

variation in the reading of test results by the same reader

Intrasubject variation

variation within individual subjects

endpoints

when conducting prognosis or survival, the endpoint we assess is death, however other endpoints such as recurrence of a disease (the cancer has come back), or interval from diagnosis to when functional impairments (such as in the case of Muscular Dystrophy) occur