gate notes

Question 1

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)?

Answer 1

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

Question 2

what is an occurance

Answer 2

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

Question 3

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

Answer 3

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

Question 4

what is an interchangeable word for population

Answer 4

group

Question 5

what is the definition of a population

and give 5 different types of common factors between populations

Answer 5

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.

Question 6

Why do we measure dis-ease occurance

Answer 6

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.

Question 7

define numerator and denominator

Answer 7

denominator- the number of people in a study population

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

Question 8

what is the first thing epidemiologists do

Answer 8

define the denominator!!!

Question 9

explain the hourglass analogy

Answer 9

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.

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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?

Question 12

explain all of pecot DIAGRAM

Answer 12

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

Question 13

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

Answer 13

MEMORISE

Question 14

is the following study outcomes categorical or numerical?

1) salt consumption
2) blood pressure level

Answer 14

numerical

Question 15

In the ideal study, using categorical data

Answer 15

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

Question 16

How is incidence calculated-word for word

Answer 16

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

Question 17

What is a requirement to use incidence

Answer 17

The data must be categorical

Question 18

When is incidence the most appropriate measure

Answer 18

when viewing diseases with a easily observable onset

Question 19

How is incidence usually presented?

Answer 19

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.

Question 20

Explain the rain puddle analogy for incidence

Answer 20

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.

Question 21

incidence EGO and CGO

Answer 21

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

Question 22

rain puddle analogy for prevalence

Answer 22

basically same as incidence but now with drizzle

Question 23

how to calculate prevalence word for word

Answer 23

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.

Question 24

What does the prevalence pool analogy illustrate?

Answer 24

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

Question 25

How do you calculate incidence with prevalence

Answer 25

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

Question 26

Define prevalence

Answer 26

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

Question 27

Why is prevalence a worse measure of occurrence than incidence

Answer 27

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

Question 28

Why is prevalence sometimes used over incidence?

Answer 28

``` 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

Question 29

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

Answer 29

memorise

Question 30

How do you calculate prevalence using categorical and numerical data

Answer 30

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

Question 31

Prevalence in EG and CG

Answer 31

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.

Question 32

When is prevalence a better measurement than incidence?

Answer 32

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

Question 33

What is a period prevalence?

Answer 33

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

Question 34

What is point prevalence

Answer 34

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

Question 35

What do period prevalence not include in their calculation?

Answer 35

• 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

Question 36

Why is period prevalence considerred a mix between incidence and prevalence

Answer 36

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

Question 37

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?

Answer 37

Because the comparison group is seldom dis-ease free

Question 38

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

Answer 38

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

Question 39

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

Answer 39

ratio of occurrences and differences in occurrences

Question 40

What is relative risk

Answer 40

EGO divided by CGO, MAY ALSO BE CALLED RISK RATIO

Question 41

what is a risk difference

Answer 41

EGO-CGO

Question 42

relative risk vs absolute risk

Answer 42

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

Question 43

what must you always do with relative risks

Answer 43

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

Question 44

what is a relative mean

Answer 44

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

Question 45

What is a relative risk reduction

Answer 45

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

Question 46

What is the RRI?

Answer 46

this is for relative risks over 1.0, | (rr-1.0)x100

Question 47

what is the no effect value

Answer 47

CGO-EGO=0 | RR=1

Question 48

wHAT IS nnt

Answer 48

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

Question 49

what is nnh/nns nnt very dependent on

Answer 49

time

Question 50

what are random errors

Answer 50

erros caused by chance

Question 51

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

Answer 51

non random errors but also called biases or systenatic erros

Question 52

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

Answer 52

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.

Question 53

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

Answer 53

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

Question 54

What is the best way to reduce recruitment error

Answer 54

choose random sample of school children from risk

Question 55

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

Answer 55

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

Question 56

what is selection bias (a form of recruitment error)

Answer 56

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

Question 57

what number of participants could cause significant recruitment error

Answer 57

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

Question 58

what are confounders

Answer 58

pther factors that make differences to the study

Question 59

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

Answer 59

1) allocate by a random process | 2) allocation by measurement

Question 60

What is the purpose of an RCT

Answer 60

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

Question 61

Why are RCTs known as experiments

Answer 61

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

Question 62

What does it mean to allocate participants by measurement

Answer 62

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

Question 63

Why are measured allocations usually called observational studies

Answer 63

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

Question 64

What are some errors that might make obsevational studies difficult to measure and how do you reduce them

Answer 64

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

Question 65

How does confounding still occur in a large RCT,

Answer 65

chance-particularly in small studies tampering with randomisation bias-surgery example and young people

Question 66

what is the way to reduce tamperring of randomisation

Answer 66

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

Question 67

why sin't RCT always possible

Answer 67

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.

Question 68

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

Answer 68

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

Question 69

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

Answer 69

the 95% confidence interval

Question 70

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

Answer 70

the 95% confidence interval

Question 71

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

Answer 71

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

Question 72

what are allocation measurment errors

Answer 72

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

Question 73

how is a maintenance error caused

Answer 73

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

Question 74

what is a conservative (maintenance) error used for

Answer 74

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

Question 75

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

Answer 75

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

Question 76

What are 4 main factors that can cause maintenance error

Answer 76

compliance, contamination co-intervention

Question 77

BOM- blind and objective measurement of disease outcomes

Answer 77

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

Question 78

How to reduce measurement of outcomes errors?

Answer 78

blinding

Question 79

Random error is due to

Answer 79

chance

Question 80

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

Answer 80

The sample is different

Question 81

What is reduced by increasing study size

Answer 81

Random sampling error

Question 82

How do you reduce random measurement error

Answer 82

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

Question 83

why does increasing study size reduce random sampling error

Answer 83

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

Question 84

what are some causes of random measurement error

Answer 84

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

Question 85

What are the 2 best ways of reudcing random measurement error

Answer 85

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

Question 86

What is meant by the randomness inherent in biological phenomena

Answer 86

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

Question 87

What is meant by random allocation error

Answer 87

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

Question 88

How do you reduce random allocation error

Answer 88

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

Question 89

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

Answer 89

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

Question 90

What is the exact definition of the 95%confidence interval

Answer 90

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

Question 91

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

Answer 91

the black squares represent the actual study values, they are called the point estimates each end is called a confidence limit

Question 92

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

Answer 92

no effect line

Question 93

confidence intervals can be used for

Answer 93

EGO< CGO RD and RR, NNT

Question 94

confidence intervals can be used for

Answer 94

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

Question 95

when the 95 confidence interval overlaps with the no effect line

Answer 95

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

Question 96

if a confidence limit is touching the no effect line,

Answer 96

it is considerred borderline statistically significant

Question 97

clinical significance

Answer 97

does a clinician find it worthwhile

Question 98

when is it often that there is no clinical significance

Answer 98

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

Question 99

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

Answer 99

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

Question 100

in a meta-analysis

Answer 100

combine the results of all the studies,

Question 101

what are the components of a meta nalysis

Answer 101

middle of diamond is the point estimate of the summary effect width of a diamond is the summary confidence interval

Question 102

Why are meya analyses done

Answer 102

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

Question 103

what is a key feature in Experimental studies

Answer 103

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

Question 104

What is a key feature of observational studies

Answer 104

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

Question 105

What is meant by a longitudinal study

Answer 105

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

Question 106

what is meant by a cross-sectional study

Answer 106

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

Question 107

what is meant as a descriptive study

Answer 107

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

Question 108

what is meant by an analytical study

Answer 108

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

Question 109

what are cohort studies also called

Answer 109

follow up or longitudinal simply because the cohorts are followed up over time

Question 110

why are confounders common in non-randomised studies

Answer 110

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

Question 111

all experimental studies are

Answer 111

longitudinal

Question 112

RCTs are the most valid study design for assessing the

Answer 112

effectiveness( benefits and harms of therappeutic or preventive interventions

Question 113

what is themain advantage of RCTs over standard cohort studies

Answer 113

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

Question 114

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

Answer 114

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.

Question 115

what are the 2 most important causes of bias in RCTs

Answer 115

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

Question 116

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

Answer 116

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

Question 117

what is a feature of a cohort study

Answer 117

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

Question 118

what are some weaknesses of cross-sectional studies

Answer 118

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

Question 119

the temporal association problem is often developed when

Answer 119

when in a study, exposure measures are made after the person has developed the study outcome it can be in some cohort studies

Question 120

what is the cohort of ecological studies

Answer 120

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

Question 121

what kind of study are ecological studies

Answer 121

they can be longitudinal or cross-sectional

Question 122

how are the results of ecological studies often displayed

Answer 122

often plotted on a graph,

Question 123

is it possible for ecological studies to be RCT?

Answer 123

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

Question 124

what are ecological studies good for

Answer 124

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

Question 125

why are ecological studies cheap to carry out

Answer 125

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

Question 126

what are the main weaknesses of ecological studies

Answer 126

great confounding