Research Chapter 15 Test 2

Front 1

Epidemiology def.

Back 1

study of the distribution (descriptive role) and determinants (analytical role) of states of health and illness in human populations.

Front 2

Epidemiology

Back 2

• An implied element of diagnosis and screening- used to id who is healthy and who is ill.
• Assist in prevention of disability
• Emphasis on populations (large groups of people)
o Focus on describing the characteristics of existing groups of people or analyzing the relationships among various health and demographic factors as they unfold within certain subgroups or across time
• Mostly nonexperimental because it looks at existing or historical data and not introduce a controlled treatment

• Experimental
• Has very specific definitions of certain terms

Front 3

Ratio:

Back 3

expresses the relationship between two numbers by dividing the numerator by the denominator (not necessarily a subset of the denominator)
Ratio= a/b
Ex: 401/35= 11.46 so 11.46:1 or there were 11.46 inversion sprains for every eversion sprain

Front 4

Proportion:

Back 4

: a fraction where the numerator is a subset of the denominator
Proportion= a/a+b
Expressed as %
Ex: 401/ (401+35)= 0.9197 so 91.97% of ankle sprains are inversion sprains

Front 5

Rate:

Back 5

proportion expressed over a particular unit of time
o Used to express the change in a health variable in the population at risk over a certain period.
o Usually a decimal
o EX: rate of new inversion sprains per year 401/12237= 0.03277
• Usually multiply each rate by 1000 to get a whole number: rate of new inversion sprains: 0.03277*1000= 32.77 per 1000 people per year
• Need to be sure to include the constant when listing the rate so the reader knows what the rate is (1000 vs 1 million people)

Front 6

Prevalence:

Back 6

expresses the proporation of a population that exhibits a certain condition at a given point in time
o Usually a proportion, not a rate
o Numerator has all of the cases of the desired condition at the time of measurement
o Denominator has all the people examined (to determine if they have the condition)
• Can be found by actual examination or survey
o Need to include a constant and point in time in which the data was collected
• Point in time can vary- giving point prevalence and period prevalence
• Point prevalence: literally the time of measurement
o Ex: do you currently have lbp?
• Period prevalence: the point in time is longer time frame determined by researcher
o Ex: have you had lbp within the last 12 months?

Front 7

Incidence:

Back 7

o Usually multiplied by a constant so that it can be expressed as a whole number
o In real world, determining incidence is complicated because people do not always seek medical care for new conditions, the care they receive occurs in many different places, and the providers define conditions differently and report them inconsistently.
o Issues to deal with:
• Determine number in population
• Use the number in the population at the midpoint of the period of study.
o Use calendar year as the reporting period with July 1 as the midpoint for determining the denominator.
• Determine who is at risk
• Does it only effect one sex, or age group?

Front 8

o Diseases or injuries of short duration

Back 8

incidence > prevalence
• Ex: common cold: most people get a new cold (high incidence), far fewer have colds at the same time ( lower prevalence)

Front 9

o Conditions of long duration

Back 9

incidence < prevalence
Ex: parkinson’s disease

Front 10

Crude rates:

Back 10

rates calculated using the entire population at risk
o Starting point for researcher’s calculations
• Ex: incidence rate of 35.63 ankle sprains for 1000 people

Front 11

Specific rates

Back 11

: specified subgroups of the population
o Athletes vs non athletes

Front 12

Adjusted rates:

Back 12

: used when one wishes to compare rates across populations with different proportions of various subgroups.
o Ex: see p 180 table 15-3

Front 13

Relative Risk

Back 13

• Go beyond describing groups and compare the probability that different groups with different characteristics will be affected by disease or injury in some way. Seek to determine the relative risk of disease or injury of two different groups.

Front 14

Risk Ratio:

Back 14

calculated by creating a ratio of the incidence rate for one subgroup and the incidence rate for another subgroup
• Ex: athletes: 139.8/1000 ankle sprains vs non athletes: 24.14/1000
• 139.8/24.14= 5.79. Athletes are 5.79 times more likely to have ankle sprains than nonathletes
Risk Ratio= [ a/ (a+b)] / [c/ (c+d)] ( use the horizontal information in table)

Front 15

Odds ratio

Back 15

when computing risk ratios is not valid, this is used to estimate relative risk.
o Only uses the nubers found within the table (not in the margins) and works the table vertically
o Simply the ratio of these two odds
Odds ratio= (a/c)/ (b/d)= ad/bc
o Ex: baseball player has one hit (3 misses) in 4 times at bat. A hit= a, Miss= b.
Proportion: a/ (a+b)= ¼= .25
Odds: hit vs misses: a/b= 1/3=.333

Front 16

Sensitivity:

Back 16

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

Front 17

Specificity:

Back 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)
B= test indicates you have the condition but you don’t ( false alarm)
C= test indicates you don’t have the condition, but you do (MISS)
Operationalize your definitions

Front 18

Positive Predictive value:

Back 18

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

Front 19

Negative predictive value:

Back 19

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

Front 20

Cross sectional studies:

Back 20

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

Front 21

Case control studies:

Back 21

: researchers identify individuals with the condition of interest (cases) and individuals without the condition of interest (controls)

Front 22

Cohort studies:

Back 22

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