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CHEP 350 > Midterm 1 > Flashcards

Midterm 1 Flashcards

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
Q

What is incidence density (incidence rate)

A

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

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26
Q

Incidence density = _______ _______

A

Incidence rate

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27
Q

ID equation

A

Total person time= the sum of every persons time at risk

We add up the period of time each person was at risk

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28
Q

what is person-time?

A
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29
Q

when is prevalence or incidence more important

A

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

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30
Q

When is CI or ID more useful

A

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

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31
Q

Summary (not real card)

A
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32
Q

CI and ID numerator and denominator

A
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33
Q

Morbidity measures vs mortality measures vs natality measures

A

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
Q

Crude vs stratum-specific estimate

A

◼ 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
Q

Crude annual death rate = _______

A

total number of deaths during calendar year

36
Q

case-fatality

A

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
Q

proportionate mortality

A

of deaths due to a specific cause/ total # of deaths

38
Q

What is inference

A

Process of gaining information about a population based on data collected from a sample

39
Q

Target population

A

Target population is the subject of inference: population whose parameters are estimated through sampling

40
Q

sample vs source vs target population

A
41
Q

what are different estimates due to

A

sampling variability

42
Q

What is the difference between a true value and a sample-based estimate

A

random error

43
Q

how do you reduce random error

A

Larger sample size
During data analysis

44
Q

What are the two ways random error can be addressed in data analysis

A

Confidence intervals
Statistical tests

45
Q

What are confidence intervals

A

◼ 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
Q

95% confidence interval formula for CI or point prevalence

A

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
Q

95% CI for incidence density

A
48
Q

What is measurement

A

Measurement is the assignment of numbers to aspects of objects or events according to one or another rule or convention.

49
Q

what do we measure with

A

Measurement instrument: a procedure or set of procedures designed to measure one or several variables of interest

50
Q

4 types of data

A

Nominal
Ordinal
Interval
Ratio

51
Q

Nominal and ordinal data

A

Qualitative/ categorical

Nominal= classification only
Ordinal= Classification + logical order

52
Q

Interval and ratio data

A

Quantitative/ continuous

Interval = Classification + Logical Order + Equal Intervals
Ratio= Classification + Logical Order + Equal Intervals + Absolute Zero

53
Q

what is the goal of our measurement

A

provide valid estimates of true disease prevalence/incidence

54
Q

What is validity

A

Does the instrument measure what it is intended to

55
Q

What is misclassification error

A

Measurement tool classify individuals into the wrong categories

56
Q

two statistics which are indicators of validity

A

sensitivity and specificity

57
Q

What are validity studies

A

◼ 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
Q

Sensitivity vs specificity

A
59
Q

What are complements of sensitivity and specificity

A

◼ 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
Q

two main sources of bias

A

misclassification bias
selection bias

61
Q

Random vs Measurement vs Selection error

A
62
Q

sensitivity equation, false negative rate

A

tp/tp+fn = sensitivity

1- sensitivity= FN rate

63
Q

specificity formula, false positive rate

A

Specificity = tn/tn+fp; 1 – Sp = false positive rate

64
Q

What is reliability? 2 focuses of reliability

A

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
Q

3 different types of reliability

A
66
Q

How to calculate reliability

A

calculate percent agreement

67
Q

What is the kappa statistic

A

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
Q

Selection bias

A

Type of systematic error related to participation
Can lead to missing data Participants only providing partial information, dropping out of study etc

69
Q

Probability sampling

A

probability of selecting a person from the population into the sample is known

70
Q

Selection probability

A

The probability that a member of the target population is selected into a sample

71
Q

Positive and negative predictive value (PPV & NPV)

A

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
Q

2 tests of validity

A
  1. Other measures of the same thing are available (already talked about this)
  2. No other (good) measure exists
73
Q

Convenience samples

A

selection probabilities are unknown

74
Q

Simple random sampling

A

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
Q

which probability sampling does statistics Canada employ

A

use complex methods sampling methods to ensure estimates are representative

76
Q

Most important procedures to handle confounding are:

A

Stratification
Standardization

77
Q

Direct vs indirect standardization

A

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
Q

Is it necessary to standardize for age when comparing measures of disease frequency

A

no, two criteria must be met
Age must be associated with place
age has to be associated with the disease of interest

79
Q

How to know if there was confounding

A

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
Q

Indirect standardization

A

the measure of interest is called the Standardized Mortality (or morbidity) Ratio (SMR)

81
Q

Indirect steps

A

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
Q

Comparisons of crude, specific, and adjusted rates

A

CHEP 350 (3 decks)

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