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gate notes Flashcards

to be king

1
Q

Why do we use the term dis-ease rather than disease rather than disease, to encompass any
health-related event (e.g. an injury, a heart attack, a death) or health-related state
(e.g. diabetes, a disability, a raised blood pressure, or quality of life)?

A

we use this term basically because it means not at ease, it can encapsulate the entire essence of unwellness rather than a limited scope implicated by the term disease.

Also implies that epidemiologists study non-pathological forms of non-ease as well

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2
Q

what is an occurance

A

a transition from a non-dis-eased state to a dis-eased state

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3
Q

When do we use events, and when do we use states?

A

we use event, when the occurance is really observable–i.e, you got hit by a car
we use state, when the occurance is not very observable,typically its like a transition.
we also note that it is a state at a point of time

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4
Q

what is an interchangeable word for population

A

group

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5
Q

what is the definition of a population

and give 5 different types of common factors between populations

A

A population is
any group of people who share a specified common factor. This factor could be a
geographic characteristic (e.g. people living in northern or southern Europe); a
demographic characteristic (e.g. an age group, gender, ethnicity or socio-economic
category); a time period (e.g. 2001); a dis-ease (e.g. heart disease); a behaviour
(e.g. smoking); a treatment (e.g. a blood pressure lowering drug); or a combination of
several of these factors.

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6
Q

Why do we measure dis-ease occurance

A

Epidemiological information on dis-ease occurrence can inform health planning and
promotion, and dis-ease prevention and treatment decisions
1) we can inform health service planners
3)_help identify causes and predictors of dis-ease occurrence and
2measuring dis-ease occurence in groups who are treated differently can determine whether treatments work.

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7
Q

define numerator and denominator

A

denominator- the number of people in a study population

numerator-the number of people from the study population whom dis-ease occurs

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8
Q

what is the first thing epidemiologists do

A

define the denominator!!!

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9
Q

explain the hourglass analogy

A

An hourglass illustrates these two essential
components of all epidemiological measures of
dis-ease occurrence. The number of people in
the study population at the beginning of an
epidemiological study is represented by the
number of grains of sand in the top bulb of the
hourglass, before any sand has flowed to the
lower bulb. The number of people in whom disease
occurs is represented by the number of
grains of sand that fall into the lower bulb.
• A key requirement of epidemiological studies is
that the dis-ease outcomes counted
(numerator) must come from a defined
population (denominator), just as the sand in
the bottom bulb must come from the top bulb.
That’s why all well-conducted epidemiological
studies begin by defining the denominator.

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10
Q

why do most epidemiological studies measure dis-ease occurrence in several populations?

A

the study objective is to determine if the occurrence in each population
differs and why it differs.

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11
Q

what is the differentiating point between epidemiological studies and other health-related sciences

A

er health-related sciences is its starting
point – the study population or denominator. While all health sciences study disease,
they have different starting points; perhaps a gene, a diseased cell, tissue,
organ, or a person. As all epidemiological studies involve the calculation of the
occurrence of dis-ease in populations, epidemiological thinking always involves
asking the question: ‘what’s the denominator?

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12
Q

explain all of pecot DIAGRAM

A

the triangle represents the PARTICIPANT population
the circle represents the STUDY SPECIFIC DENOMINATORS
the square represents the NUMERATOR

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13
Q

One could measure the occurrence of ‘no dis-ease’ in EG (=
c/EG) and CG (=d/CG) and this is done in some studies, particularly diagnostic test
accuracy studies

A

MEMORISE

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14
Q

is the following study outcomes categorical or numerical?

1) salt consumption
2) blood pressure level

A

numerical

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15
Q

In the ideal study, using categorical data

A

everyone in EG and CG ultimately gets
classified as either having a dis-ease outcome (a or b) or not having dis-ease (c or
d). Therefore the number of people in EG should equal the number of people in a &
c. Similarly the number of people in CG should equal the number of people in b & d

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16
Q

How is incidence calculated-word for word

A

incidence is calculated by counting the number of onsets of dis-ease during a period of time and then dividing the numerator by the number of people in the study

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17
Q

What is a requirement to use incidence

A

The data must be categorical

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18
Q

When is incidence the most appropriate measure

A

when viewing diseases with a easily observable onset

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19
Q

How is incidence usually presented?

A

its usually presented as the proportion (or percentage) of people from the study
population (or more commonly from the exposure or comparison groups within the study
population) in whom a dis-ease event occurs during a specified time period.

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20
Q

Explain the rain puddle analogy for incidence

A

cloud is the population
the numerator is analogous to the number of rain drops falling into the pool over 1 hour
the denominator is the total number of possible raindrops in the population cloud.

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21
Q

incidence EGO and CGO

A

a/EG during time T(over time period)
basically, the number of yes outcomes divided by the number of people in EG during time T

incidence is a measure of occurrence

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22
Q

rain puddle analogy for prevalence

A

basically same as incidence but now with drizzle

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23
Q

how to calculate prevalence word for word

A 
is the alternative
measure of Dis-ease occurrence to
incidence and is calculated by
counting the number of people with
a dis-ease at a point of time (the
numerator) and then dividing by the
number of people in the study group
at that point in time (the
denominator). Prevalence is the
measure of dis-ease occurrence
used when the transition from a non
dis-ease to a dis-ease state cannot
easily be observed and counted.
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24
Q

What does the prevalence pool analogy illustrate?

A

The prevalence pool analogy illustrates that prevalence is a static measure of dis-ease
status like the amount of water in a pool at a point in time

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25
Q

How do you calculate incidence with prevalence

A

measure the prevalence of dis-eases at two points of time (analogous to
measuring the amount of water in the pool at two time points) and calculate the change
in prevalence. The difference in prevalence between the two time points is in fact a
measure of the incidence of dis-ease over the period between the two time points

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26
Q

Define prevalence

A

The ammount of dis-ease in a population at a point in time

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27
Q

Why is prevalence a worse measure of occurrence than incidence

A

it is a less useful measure than incidence for investigating causes of dis-ease
high incidence of dis-ease could result in either a high or low prevalence depending on death rate and cure rate. Therefore a population with high incidence of disease could have low prevalence

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28
Q

Why is prevalence sometimes used over incidence?

A 
Prevalence is the
measure of dis-ease occurrence
used when the transition from a non
dis-ease to a dis-ease state cannot
easily be observed and counted

in like the case of diabetes or something

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29
Q

Incidence is typically calculated separately in the exposure and comparison groups in the
study population (i.e. in EG and in CG; see box below). Therefore EG and CG are
considered to be separate denominators within the initial overall study population

A

memorise

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30
Q

How do you calculate prevalence using categorical and numerical data

A

For a categorical outcome such as diabetes, prevalence is calculated as a proportion
(e.g. diabetes prevalence in 60-70 year old Maori women is 35%). For numerical
outcomes such as blood cholesterol, prevalence can be calculated by reclassifying the
numerical data into categories (e.g. high or low cholesterol levels) and then calculating
the proportion of people with high levels. For example, the prevalence of high blood
cholesterol (say, > 6.5 mmol/L) in patients waiting for bypass surgery could be 500 per
1000 patients (50%). Alternatively the numerical data can be presented as an average or
mean value (e.g. the mean cholesterol in patients waiting for heart surgery is 6.5
mmol/L). This is done by adding up the cholesterol values of all participants (i.e. the
sum) and then dividing by the number of participants. While this average measure is not
traditionally described as a prevalence measure, it has much in common with prevalence
measures and is another way of presenting the same information

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31
Q

Prevalence in EG and CG

A

Prevalence in EG (EGO) = number of ‘yes’ outcomes from EG ÷ number in EG or = a ÷ EG
Prevalence in CG (CGO) = number of ‘yes’ outcomes from CG ÷ number in CG or = b ÷ CG

As with incidence, in the GATE Notes we use the generic term ‘Exposure Group Occurrence’
(EGO) to describe the prevalence in the exposure group and Comparison Group Occurrence
(CGO) for prevalence in the comparison group.

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32
Q

When is prevalence a better measurement than incidence?

A

If the disease frequency is very high. Sometimes diseases with observable onsets are still better measured with prevalence

…a diagnosis of significant asthma is
made by asking a person if they have had two or more asthma attacks, severe enough to
limit normal activities, in the previous one-year period. Once we have defined what
significant asthma is, we then define the prevalence of significant asthma as the
proportion of a group of people, who at the time of asking have had at least two severe
asthma attacks in the previous one-year period. This is called period prevalence
because the outcome definition (numerator definition) depends on the time period
specified. In contrast, the more common measure of prevalence is often called point
prevalence because the outcome (e.g. diabetes) definition does not take any previous
time period into account and is simply measured at one point in time

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33
Q

What is a period prevalence?

A

prevalence when the outcome definition (numerator definition) depends on the time period
specified

e.g-the proportion of a group who at the time of asking had at least 2 severe asthma attacks in the previous one -year period

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34
Q

What is point prevalence

A

In contrast, the more common measure of prevalence is often called point
prevalence because the outcome (e.g. diabetes) definition does not take any previous
time period into account and is simply measured at one point in time

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35
Q

What do period prevalence not include in their calculation?

A

• Period prevalence calculations do not include the actual number of episodes an
individual person has in the calculation. So in the asthma example above, whether a
person has three episodes or ten episodes, they are only counted once in the numerator

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36
Q

Why is period prevalence considerred a mix between incidence and prevalence

A

Period prevalence is a mix of incidence and prevalence because it initially involves
defining the presence of dis-ease based on the number of onsets that have occurred
over a period of time, and then converting this into a single measure of di-ease at a point
in time

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37
Q

why is it important to measure the occurrence of dis-ease both in the group of people who are exposed and in the group who are not exposed?

A

Because the comparison group is seldom dis-ease free

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38
Q

why might it be more appropriate to describe comparisons of dis-ease occurrence as “estimates of association” rather than “estimates of effect”

A

The term effect infers a causal relationship between the exposure and the outcome, and there are several further steps required before one can be confident that an association is causal

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39
Q

what are the two main ways to compare two dis-ease occurrences

A

ratio of occurrences and differences in occurrences

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40
Q

What is relative risk

A

EGO divided by CGO, MAY ALSO BE CALLED RISK RATIO

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41
Q

what is a risk difference

A

EGO-CGO

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42
Q

relative risk vs absolute risk

A

risk difference is an absolute risk as it has units, relative risk has no units, and we don;t really have a number

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43
Q

what must you always do with relative risks

A

explain a relative risk by stating that risk in one spcified group is say 2 times higher than in another group

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44
Q

what is a relative mean

A

if disease occurence measures are calculated as means , then the relative comparison of two mean scores would yield a relative mean

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45
Q

What is a relative risk reduction

A

a relative risk that is less than 1.0, because it is reduced below 1.0 (the no effect value).

The relative risk reduction is usually expressed as a percentage and is calculated by subtracting the relative risk from 1.0and then multiplying by 100.

e.g, group 1 is 7/100
comparison group is 10/100
the RR= 7/10
RRR=(1.0-0.7)X100

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46
Q

What is the RRI?

A

this is for relative risks over 1.0,

(rr-1.0)x100

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47
Q

what is the no effect value

A

CGO-EGO=0

RR=1

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48
Q

wHAT IS nnt

A

the number of people needed to be treated to prevent 1 event.
iNNT=1/RISK DIFFERENCE

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49
Q

what is nnh/nns nnt very dependent on

A

time

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50
Q

what are random errors

A

erros caused by chance

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51
Q

what are erros caused by problems with how the study is desiged or conducted called

A

non random errors but also called biases or systenatic erros

52
Q

why would no single study ever measure the exact truth in the whole populatio even if it is a perfect study

A

a single study is always conducted on a sample of the whole population because it is not possible to include everyone in a single study and every sample will be different.

53
Q

why are recruitment erros usually described as an external validity error?

A

because when it is present the study findings may not be applicable to a wider population.

54
Q

What is the best way to reduce recruitment error

A

choose random sample of school children from risk

55
Q

give an example of when it might not be necessary to account for recruitment error

A

e.g, testing an antibiotic, it is unnecesary to recruit participants who are representative of a specified external population, you just need to know whether the antibiotics work or not

56
Q

what is selection bias (a form of recruitment error)

A

when there are 2 overlapping triangles on pecot frame,

when the exposure group are recruited from a very different source from the participants allocated to the comparison group

57
Q

what number of participants could cause significant recruitment error

A

a response rate of less than about 70-% of those invited could cause a significant recruitment error in prevalence studies like the physical activity in school children study described above

58
Q

what are confounders

A

pther factors that make differences to the study

59
Q

what are the two common ways of allocating participants to EG and CG in epidemiological studies

A

1) allocate by a random process

2) allocation by measurement

60
Q

What is the purpose of an RCT

A

give all participants an equal chance of being allocated to EG or Cg so that all groups are similar at the beginning of the study

61
Q

Why are RCTs known as experiments

A

the investigators actively experiment on participants by controlling the allocation process.
experimenters do determine how the participants are allocated

62
Q

What does it mean to allocate participants by measurement

A

participants are measured to determine if they are exposed to the factor being investigated in the study

63
Q

Why are measured allocations usually called observational studies

A

exposures of interest are observed in order to determine if participants should be allocated to eg or cg. These observational studies are not considered to be experiments because the investigator does not determine how the participants are allocated

64
Q

What are some errors that might make obsevational studies difficult to measure

and how do you reduce them

A

embarassment;causing under reporing, over reporting

using biological tests and well designed validated questionnaires

THE EG AND CG are frequently quite different from each other (e.g, smokers tend to exhibit other risky behaviors as well as smoking). These differences may be confounders. To be a confounder, it must directly impact the result being studied-brown eyes analogy

65
Q

How does confounding still occur in a large RCT,

A

chance-particularly in small studies

tampering with randomisation bias-surgery example and young people

66
Q

what is the way to reduce tamperring of randomisation

A

concealment of allocation- basically add another investigator to open envelope, write down treatment group and name

67
Q

why sin’t RCT always possible

A

it is only possible when the exposure intervention investigated is consdered to be at least as safe as the comparison intervention,

n.b, when stents were unknown to cause longer lifespan, it was ethical to test them in rct with placebo

now that stents were known conclusively to cause longer lifespan, it is now unethical to test them in rct with a placebo.

68
Q

When are dotted and horizontal verticle lines used within the GATE FRAME

A

to indicate when there may be more than 2 exposure groups and more than 2 outcome groups

69
Q

What do we use to describe the amount of random error in the study results

A

the 95% confidence interval

70
Q

What do we use to describe the amount of random error in the study results

A

the 95% confidence interval

71
Q

IN AN IDEAL EPIDEMIOLOGICAL STUDY, THE PARTICIPANTS ALLOCATED TO THE exposure group and the comparison group would be

A

so similar that in the absence of the specific exposure being studied, the 2 groups would have the same occurence of outcomes

If there is a difference between EGO or CGO , it would be due to the study exposure

72
Q

what are allocation measurment errors

A

measurement errors that result in participants being allocated to the wrong exposure group

73
Q

how is a maintenance error caused

A

if some participants’ exposure status cahnges or some are lost to follw up

74
Q

what is a conservative (maintenance) error used for

A

usually a small number of maintenance error would occur and the size of the error would be similar to both Eg and CG. i call this the conservative maintenance error.

When this error happens, the error will underestimate the true effect of the exposure on the study outcomes

it is preferable to not knowing whether the error will exaggerate or underestimate the true study effect estimates

75
Q

How do you keep the degree of maintenance error similar to EG and CG

A

keep both the participants and study practitioners blind to whether they are receiving the exposure or comparison exposure

76
Q

What are 4 main factors that can cause maintenance error

A

compliance, contamination co-intervention

77
Q

BOM- blind and objective measurement of disease outcomes

A

this thing can be summarised into a question: were the people who MEASURED the disease outcomes were unaware (blind) to the participant’s exposure status and were these measurements made objectively (using measurement instruments that were not influenced by subjective factors like human error)

e.g, a measurer who knows that a smoker may assume the smoke killed him. This error is completely related to the measurer

78
Q

How to reduce measurement of outcomes errors?

A

blinding

79
Q

Random error is due to

A

chance

80
Q

Why is it likely that ever study on the same thing is likely to give a different result

A

The sample is different

81
Q

What is reduced by increasing study size

A

Random sampling error

82
Q

How do you reduce random measurement error

A

increasing the number of times a factor is measured on each participant

83
Q

why does increasing study size reduce random sampling error

A

the bigger the sample chosen, the smaller the differences will be between the sample and the total population

84
Q

what are some causes of random measurement error

A

typically can be environmental or some other factor that influences the operator’s ability to detect the blood pressure sounds accurately- this includes background sound or some shit

85
Q

What are the 2 best ways of reudcing random measurement error

A

take multiple measurements and average them, or use an automatic objective instrument

86
Q

What is meant by the randomness inherent in biological phenomena

A

inherent variability in all measurements of biological phenomena-as theobject could be changin

87
Q

What is meant by random allocation error

A

The people in EG and CG can differ purely due to chance

88
Q

How do you reduce random allocation error

A

undertake a larger study, so large numbers are randomised to EG or CG

89
Q

what does EGO=9.0 with a 95% confidence interval from 8.0-10.0 mean

A

there is about a 95%probability that the true value of EGO in the whole population of interest from which the study participants were recruited lies between 8.0 and 10.0

MUCH EMPHASIS that it is from where they were RECRUITED Ffrom

90
Q

What is the exact definition of the 95%confidence interval

A

If the same study is repeated many times using different random samples recruited from the whole population of interest the approximately 95% of the confidence intervals would include the true value, that would have been calculated if the whole population was in a single study

91
Q

in a confidence interval what are the filled in black squares and what are the ends of a confidence interval called

A

the black squares represent the actual study values, they are called the point estimates

each end is called a confidence limit

92
Q

When there is no overlap in the CIs for EGO and CGO, the confidence intervals for RD or RR will not cross the

A

no effect line

93
Q

confidence intervals can be used for

A

EGO< CGO RD and RR, NNT

94
Q

confidence intervals can be used for

A

EGO CGO RD and RR, NNT

all measures of disease frequency and estimate of effect

can be calculated for both categorical outcomes and numerical variables

95
Q

when the 95 confidence interval overlaps with the no effect line

A

there may be too much random error to determine if there is real difference between EGO and CGO

96
Q

if a confidence limit is touching the no effect line,

A

it is considerred borderline statistically significant

97
Q

clinical significance

A

does a clinician find it worthwhile

98
Q

when is it often that there is no clinical significance

A

a small but statistically significant effect with a narrow confidence interval may not be considered to be clinically significant within the confidence interval (milidu)

or whether the benefit is too small

99
Q

meta analyses are the reason why confidence intervals for EGO and CGO differences in the underlying population are

A

misinterpreted as yes/no tests of whether there is a difference between EGO and CGO.

just because values cross, does not necessarily mean that there is no beneficial treatment effect. it usually means that none of the individual studies are large enough to demonstrate there is a real treatment benefit

100
Q

in a meta-analysis

A

combine the results of all the studies,

101
Q

what are the components of a meta nalysis

A

middle of diamond is the point estimate of the summary effect

width of a diamond is the summary confidence interval

102
Q

Why are meya analyses done

A

they are an alternative to conducting one large study

combine the results of multiple RCTs that individually have too much random error to demonstrate whether or not the intervention has a real effect

103
Q

what is a key feature in Experimental studies

A

participants allocated to EG and CG by the investigators

this includes RCTs because it is the investigators whoo in effect flip a coin to decide who goes into EG or CG

n,b if an investigator allocates participants to EG or CG using a non-random process, its still counted as an experimental study

104
Q

What is a key feature of observational studies

A

when participants are allocated to EG and CG by measurement,

the main reason it is called observational is because the investigators do not actively experiment on the participants. They passively observe what the participants have done to themselves

105
Q

What is meant by a longitudinal study

A

it is a study where after participants have been allocated to EG and CG, they are followed over time.

Longitudinal-i.e long.

Outcomes often calculated during the follow up period

106
Q

what is meant by a cross-sectional study

A

participants are allocated to EG and CG by measurement, at the same time as outcomes are measured

107
Q

what is meant as a descriptive study

A

descriptive studies describes the frequency of health related behaviours, risk factors and outcomes

108
Q

what is meant by an analytical study

A

an analytical study analyses the descriptions of frequency of health-related behaviours, risk factors and outcomes

109
Q

what are cohort studies also called

A

follow up
or longitudinal

simply because the cohorts are followed up over time

110
Q

why are confounders common in non-randomised studies

A

often clinical decisions to treat patients or voluntary uptake of some lifestyle practices do not happen at random

111
Q

all experimental studies are

A

longitudinal

112
Q

RCTs are the most valid study design for assessing the

A

effectiveness( benefits and harms of therappeutic or preventive interventions

113
Q

what is themain advantage of RCTs over standard cohort studies

A

they are much less prone to confounding because the randomisation process is designed to produce an EG and CG with very similar characteristics

114
Q

What are some practical and ethical reasons why many important questions cannot be investigated using the RCT design

A

potentially dangerous or illicit drugs may cause ethical concerns

RCTs are often conducted in artificial environments and often only highly motivated participants may be recruited, so they may not represent the usual population.

115
Q

what are the 2 most important causes of bias in RCTs

A

poor allocation processes and poor maintenance of participants in their allocated groups

116
Q

clarify ; why dosen’t it make sense to design an experimental cross-sectional study?

A

because the participants would be exposed to the study intervention ( like a drug or placebo) at the same time as the outcomes- so there would be no time for the intervention to have an effect

117
Q

what is a feature of a cohort study

A

the participants are allocated to the appropriate EG or CG after being assessed

purely passive

118
Q

what are some weaknesses of cross-sectional studies

A

it can be hard to find a real association-

if smoking causes asthma, but most people who develop asthma then stop smoking, it won’t be possible to find the real association between smoking and asthma

reverse causuality- hard to tell

temproal association problem (cause and effect) is the broad umbrella term

119
Q

the temporal association problem is often developed when

A

when in a study, exposure measures are made after the person has developed the study outcome

it can be in some cohort studies

120
Q

what is the cohort of ecological studies

A

instread of groups of individuals, it measures groups of populations

e.g, death rate from a group of low income countries and a group of high income countries

121
Q

what kind of study are ecological studies

A

they can be longitudinal or cross-sectional

122
Q

how are the results of ecological studies often displayed

A

often plotted on a graph,

123
Q

is it possible for ecological studies to be RCT?

A

yes-
example givn is a study to determine whether tv ads reduce road traffic injuries across different regions across countries.
Different regions could be randomised to receive ads or not
and regional stats assessed

124
Q

what are ecological studies good for

A

investigating both risk factors and intervention effects

often they are great at assessing the effects of rare exposures or exposures that are almost universal in some populations and uncommon in other populations

125
Q

why are ecological studies cheap to carry out

A

they generally use data that has already been collected for other purposes

126
Q

what are the main weaknesses of ecological studies

A

great confounding

Pophealth Questions (7 decks)

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