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CHEP 350 > Midterm 1 > Flashcards

Midterm 1 Flashcards

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1
Q

What is epidemiology

A

The science of understanding the distribution and causes of population health so that we may intervene to prevent disease and promote health.

Quantitative
unique vocabulary
interdisciplinary

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2
Q

Descriptive vs analytical studies

A

Descriptive focuses on distribution
Analytical focuses on determinants and relationships between them

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3
Q

Two core functions of epidemiology

A
  1. identifying causes of health
  2. So that we may intervene (intervention)
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4
Q

What is a cause

A

cause is something that makes a differences or produces change

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5
Q

What are some challenges for epidemiology

A

Chronic diseases
Current conceptual movements

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6
Q

Most epidemiological studies are ___________

A

observational

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7
Q

What is confounding

A

Confounding is a distortion of an exposure-outcome association brought about by the association of another factor(s) with both outcome and exposure

The effect of the exposure is mixed together with the effect of another variable leading to bias

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8
Q

What is selection bias

A

Distortions that result from procedures used to select subjects and from factors that influence participation in the study

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9
Q

What is information/Measurement bias? Defining feature?

A

Distortion in the measure of effect caused by a lack of accurate measurements of exposure or disease status

Defining feature: occurs at data collection stage, misclassification of exposure is the main source of error

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10
Q

objectives and major dimensions of descriptive epidemiology

A

Objectives: Permit evaluation of trends in health and disease and comparisons among countries and sub groups, evaluation of health services, hypothesis generation

Major Dimensions: Assumption that diseases do not occur at random
Three standard questions are typically posed to characterize disease distribution

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11
Q

What are the three standard questions for descriptive epidemiology

A

Who gets the disease (person)?
Where does the disease occur (place)?
When does the disease occur (time)?

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12
Q

what is a population

A

A population is a collection of individuals, at moments in time, defined by at least one organizing characteristic

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13
Q

What are the measures of disease frequency that should be taken into account?

A

Number of individuals affected
Size of population
Time/Time period

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14
Q

What is prevalence

A

Measures existing cases of a disease at a particular point in time or over a period of time
The porbability that a member of the population has the disease

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15
Q

Point prevalence

A

Proportion of people who possess a certain attribute at a certain point in time

of existing cases at a given point in time/ total population at a given point in time

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16
Q

what factors can increase prevalence

A

Longer duration
Increased incidence
In-migration
Out-migration of healthy
better diagnosing

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17
Q

What is incidence? 3 key concepts?

A
  • Quantifies number of new cases of disease that develop in a population at risk during a specified time period. Can be measured as a rate or a proportion

3 key concepts:
New disease events, or first occurrence
Population at risk can’t have disease already, should have relevant organs
Time must pass for a person to move from health to disease

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18
Q

Cumulative incidence

A

Number of new cases of a disease in a given time/ Total population at risk

Cumulative incidence is the proportion of an initially disease free group of individuals who develop the disease within a specified period of observation

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19
Q

Other words for cumulative incidence

A

Cumulative incidence = incidence proportion = Risk

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20
Q

Artifactual influences on changes in rates over time

A

Changes in the ability to recognize the disease
Changes in the efforts to recognize disease
Changes in the definition of the disease

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21
Q

Limitations of cumulative incidence/incidence proportion (2)

A
  1. Cumulative incidence calculation assumes that you have followed the entire population for the entire follow-up period
  2. cumulative incidence doesn’t explicitly account for the passage of time
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22
Q

Incidence proportions can only be directly calculated in _______ populations

A

closed/stationary

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23
Q

Stationary vs dynamic populations

A

Dynamic: allows for movement in and out of the population
Stationary: does not allow for movement in or out of a population. Population remains same never losing nor adding others

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24
Q

Censored observations

A

Measurements on those subjects who do not complete the entire study period for reasons other than developing the study outcome

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25
What is incidence density (incidence rate)
Describe how rapidly health events are occurring in a population of interest True rate because it directly integrates time into the denominator Does not make assumption to complete follow-up
26
Incidence density = _______ _______
Incidence rate
27
ID equation
Total person time= the sum of every persons time at risk We add up the period of time each person was at risk
28
what is person-time?
29
when is prevalence or incidence more important
In general, Incidence is more important when thinking of etiology of the disorder, prevalence when thinking of societal burden of the disorder including the costs and resources consumed as a result of the disorder
30
When is CI or ID more useful
CI is most useful if interest centers on the probability than an individual will become ill over a specified period of time. ID is preferred if interest centers on how fast the new cases are occurring in the population
31
Summary (not real card)
32
CI and ID numerator and denominator
33
Morbidity measures vs mortality measures vs natality measures
Morbidity measures pertain to the sickness, disease or disability within specific populations. Mortality measures describe the frequency of death in populations. Natality measures measure the frequency and the probability of births within specific populations
34
Crude vs stratum-specific estimate
◼ Crude estimate – a measure of disease occurrence for an entire population ◼ Stratum-specific estimate – a measure of disease occurrence for a population subgroup (e.g, age, sex)
35
Crude annual death rate = _______
total number of deaths during calendar year
36
case-fatality
Number of deaths due to the disease in a specified period of time/Number of cases of the disease in the same period of time
37
proportionate mortality
of deaths due to a specific cause/ total # of deaths
38
What is inference
Process of gaining information about a population based on data collected from a sample
39
Target population
Target population is the subject of inference: population whose parameters are estimated through sampling
40
sample vs source vs target population
41
what are different estimates due to
sampling variability
42
What is the difference between a true value and a sample-based estimate
random error
43
how do you reduce random error
Larger sample size During data analysis
44
What are the two ways random error can be addressed in data analysis
Confidence intervals Statistical tests
45
What are confidence intervals
◼ Measures of disease frequency such as prevalence are point estimates of the population parameter. ◼ How well the point estimate estimates the parameter (i.e., its precision) depends on sampling (random) error. ◼ One way of estimating the precision of a point estimate is to calculate a confidence interval
46
95% confidence interval formula for CI or point prevalence
95%CI= p+/- 1.96√p(1-p)/(n+4) where p = (x + 2)/(n + 4) p refers to the adjusted sample proportion (either cumulative incidence or prevalence stated as a decimal fraction, for example, .10) n is the appropriate denominator x is the appropriate numerator
47
95% CI for incidence density
48
What is measurement
Measurement is the assignment of numbers to aspects of objects or events according to one or another rule or convention.
49
what do we measure with
Measurement instrument: a procedure or set of procedures designed to measure one or several variables of interest
50
4 types of data
Nominal Ordinal Interval Ratio
51
Nominal and ordinal data
Qualitative/ categorical Nominal= classification only Ordinal= Classification + logical order
52
Interval and ratio data
Quantitative/ continuous Interval = Classification + Logical Order + Equal Intervals Ratio= Classification + Logical Order + Equal Intervals + Absolute Zero
53
what is the goal of our measurement
provide valid estimates of true disease prevalence/incidence
54
What is validity
Does the instrument measure what it is intended to
55
What is misclassification error
Measurement tool classify individuals into the wrong categories
56
two statistics which are indicators of validity
sensitivity and specificity
57
What are validity studies
◼ In these studies, a group of individuals are administered two tests: 1) first, a gold standard test (ie., criterion standard) in which there are no misclassification errors; 2) second, another (experimental) test purportedly measuring the same thing but may be cheaper, shorter, less invasive…. ◼ This allows for each respondent to be classified into one of four groups
58
Sensitivity vs specificity
59
What are complements of sensitivity and specificity
◼ Complementary means probabilities add up to 1. ◼ The complement of sensitivity is the false-negative rate (ie., 1-sens=fn rate). ◼ The complement of specificity is the false-positive rate (ie., 1-sp=fp rate)
60
two main sources of bias
misclassification bias selection bias
61
Random vs Measurement vs Selection error
62
sensitivity equation, false negative rate
tp/tp+fn = sensitivity 1- sensitivity= FN rate
63
specificity formula, false positive rate
Specificity = tn/tn+fp; 1 – Sp = false positive rate
64
What is reliability? 2 focuses of reliability
Does the instrument measure something in a reproducible fashion 1. Test/method or observer/rater 2. within or between test/methods or observer/rater
65
3 different types of reliability
66
How to calculate reliability
calculate percent agreement
67
What is the kappa statistic
Measure of reliability The kappa statistic is the excess agreement over that expected by chance (EP), divided by the potential excess Kappa = (OP-EP)/(1-EP) OP= (a+d)/n, where n = a+b+c+d EP = [(a+b/n) X (a+c/n)] + [(c+d/n) X (b+d/n)] 1-0, 1 = complete agreement, 0= agreement is equal to that expected by chance, negative indicates agreement less than expected by chance
68
Selection bias
Type of systematic error related to participation Can lead to missing data Participants only providing partial information, dropping out of study etc
69
Probability sampling
probability of selecting a person from the population into the sample is known
70
Selection probability
The probability that a member of the target population is selected into a sample
71
Positive and negative predictive value (PPV & NPV)
PPV: Probability that a person has the disease given that he or she tests positive NPV: the probability that a person is disease free given that he or she tests negative
72
2 tests of validity
1. Other measures of the same thing are available (already talked about this) 2. No other (good) measure exists
73
Convenience samples
selection probabilities are unknown
74
Simple random sampling
each member of a population has the same chance of being selected into a sample; that is, the selection probability for each member of the population is the same
75
which probability sampling does statistics Canada employ
use complex methods sampling methods to ensure estimates are representative
76
Most important procedures to handle confounding are:
Stratification Standardization
77
Direct vs indirect standardization
Direct: selecting a standard population and usign the age structure from the standard population and multiplying it by stratum-specific disease frequency rates form the two populations being compared (DSMR) Indirect: Used when there is missing data and/or cell size may be too small. Selects a standard population and uses the stratum-specific disease frequency rats from the standard population and multiplying them by the age structure of the population with missing data
78
Is it necessary to standardize for age when comparing measures of disease frequency
no, two criteria must be met Age must be associated with place age has to be associated with the disease of interest
79
How to know if there was confounding
Calculate Rc and compare to DSM If DSMR = Rc then no condounding was performed Rc= Crude pop A/ Crude pop B When DSMR =/ Rc standardized rates should be reported
80
Indirect standardization
the measure of interest is called the Standardized Mortality (or morbidity) Ratio (SMR)
81
Indirect steps
Step 1: calculated expected # of deaths if the age-specific death rates were the same as in the standard population Step 2: Calculate SMR SMR = Observed deaths/Expected deaths
82
Comparisons of crude, specific, and adjusted rates

CHEP 350 (3 decks)

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