Research15

Question 1

How is epidemiology defined by the text?

Answer 1

As the “study of the distribution and determinants of states of health and illness in human populations.”

Question 2

What statistical means are used to describe various health and illness phenomena?

Answer 2

Ratios, proportions, and rates

Question 3

What does a ratios express?

Answer 3

The relationship between two numbers by dividing the numerator by the denominator; ratio= a/b

Question 4

What does a proportion represent?

Answer 4

A fraction in which the numerator is a subset of the denominator; proportion = a/ (a+b); converted to percentages

Question 5

What is a rate?

Answer 5

A proportion expressed over a particular unit of time; used to express the change in a health variable in the population at risk over a certain period

Question 6

How do epidemiologist use ratios, percentages, and rates?

Answer 6

To express prevalence and incidence

Question 7

What does prevalence express?

Answer 7

Proportion of a population that exhibits a certain condition at a given point in time; prevalence= existing cases/population examined at a given point in time

Question 8

What is incidence?

Answer 8

The rate of new cases of a condition that develop during a specific period of time; incidence = new cases during time period / population at risk during time period

Question 9

What is the relationship between incidence and prevalence?

Answer 9

The relationship depends on the nature of the condition being examined. For disease and injury that are of short duration, incidence is often greater than prevalence. For conditions that are of long duration, incidene is often lower than prevalence.

Question 10

What are the three forms of rates used to compare the sample with the population norms?

Answer 10

Crude rates- rates calculated using the entire population at risk; specific rates- rates for specified subgroups of the population; adjusted rates- used when one wishes to compare rates across populations with different proportions of various subgroups

Question 11

What is relative risk?

Answer 11

the probability that different populations with different characteristics ill be affected by disease or injury in some way

Question 12

What are the two ways in which relative risk is calculated?

Answer 12

using risk ratios and odds ratios

Question 13

How is a risk ratio calculated?

Answer 13

by creating a ratio of the incidence rate for one subgroup and the incidence rate for another subgroup; risk ratio= [a/(a+b)] / [c/(c+d)]

Question 14

How is an odds ratio calculated?

Answer 14

used to estimate relative risk among subgroups; odds ratio= (a/c)/(b/d)= ad/bc

Question 15

What are the four key proportions used to compare usefulness of the test being evaluated to a criterion test that is considered the “gold standard”?

Answer 15

sensitivity, specificity, positive predictive value, and negative predictive value

Question 16

What is sensitivity?

Answer 16

the proportion or percentage of individuals with a particular diagnosis who are correctly identified as positive by the test; sensitivity= a/(a+c)

Question 17

What is specificity?

Answer 17

the proportion or percentage of individuals without a particular diagnosis who are correctly identified as negative by the test (rate of correct rejections); specificity= d/(b+d)

Question 18

How are Receiver-operative characteristics (ROC) curves used?

Answer 18

incorporate both the physical ability and the response criterion of a psyophysical decision into one curve

Question 19

What is used to calculate a likelihood ratio?

Answer 19

sensitivity and specificity; likelihood ratio of a positive test= sensitivity%/ (100-specificity%); likelihood ratio of a negative test= (100-sensitivity%)/ specificity %

Question 20

What is the positive predictive value?

Answer 20

percentage of individuals identified by the test as positive who actually have the diagnosis; positive predictive value= a/(a+b)

Question 21

What is the negative predictive value?

Answer 21

the percentage of those identified by the test as negative who actually do not have the diagnosis; negative predictive value= c/(c+d)

Question 22

What are three common nonexperimental epidemiological designs?

Answer 22

cross-sectional, case-control, and cohort designs

Question 23

How are cross-sectional designs used?

Answer 23

to document the health status of a group at a particular point in time

Question 24

How are case-control designs used?

Answer 24

researchers identify individuals with the condition of interest and individuals without the condition of interest then look to past and present for risk factors; start with “effects” and looks for “causes”

Question 25

How are cohort designs used?

Answer 25

researchers identify individuals with various risk factors and look into the future to see if the condition of interest develops

Question 26

What are some advantages to the case-control study?

Answer 26

that ability to study a reasonable number of individuals with relatively rare conditions without needing to observe the entire population at risk for long periods, enables researchers to study things that might not otherwise be ethical to study

Question 27

What is one of the main concerns with case-control studies?

Answer 27

the manner in which the presumed causes are documented or identified; not all factors may be well documented