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POPHLTH 111 > GATE notes > Flashcards

GATE notes Flashcards

1
Q

Define epidemiology

A

study of how much disease occurs in groups (or populations) and of the factors that determine differences in disease occurrence between different groups

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2
Q

define occurence

A

the transition from a non diseased state to a diseased state

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3
Q

What is categorical data

A

Data that is put into categories

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4
Q

What is numerical data

A

Data that takes on numerical values

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5
Q

Define population

A

a group of people who share a specified common factor e.g. geographic, demographic, ethnicity, time period, behaviour etc.

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6
Q

What does PECOT stand for?

A 
Population 
Exposure group (can have more than one)
Comparison group
Occurence
Time
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7
Q

What is the occurrence formula?

A

numerator/denominator

people with disease/population

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8
Q

What is incidence?

A

a measure of time used for easily observable events and DEATHS.
calculated by counting the number of ONSETS of disease occurring DURING A PERIOD OF TIME.
n/d/t
like a movie

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9
Q

What is prevalence?

A

like taking a photo
used for not easily observable events e.g. diabetes.
calculated by counting the number of people with a disease AT ONE POINT IN TIME divided by population
prevalence is often a measure at two points in time
prevalence is the measure of amount of disease in a population.

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10
Q

What is an example of a disease with high prevalence and low incidence?

A

obesity

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11
Q

What is an example of a disease with high incidence and low prevalence?

A

cold/flu – as people leave prevalence pool as people get cured fast

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12
Q

What is the difference between period prevalence and point prevalence?

A

Point prevalence - would be used for disease where the outcome only occurs once e.g. people with diabetes.
Period prevalence - used for diseases which may be hard to measure at a specific point in time e.g. asthma - so they use a time period in the past and ask questions based on that.

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13
Q

What is an ecological study?

A

compares groups of populations rather than groups of individuals e.g. countries

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14
Q

What is a cohort study?

A

measures exposure and then outcome later on in time. e.g. alcohol use and then the prevalence of solvent users in that group.

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15
Q

What is a cross sectional study?

A

measuring exposure and outcome at the same time

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16
Q

What is used to measure an event and what is used to measure a state?

A

Incidence for event

Prevalence for state

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17
Q

What is the Denominator?

A

the number of people in a study population

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18
Q

What is the Numerator?

A

the number of people from the study population (i.e. from the denominator) in whom dis-ease occurs.

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19
Q

What does the circle represent in the GATE frame?

A

the study- specific Denominators (we call them groups).

EG and CG

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20
Q

In a study to do with salt levels and blood pressure how would you split the numerators and denominators?

A

In the salt and blood pressure example, salt intake could still be categorically classified into high and low intake categories, but the blood pressure levels can remain as numerical data and the average (or mean) blood pressure can be calculated in each group.

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21
Q

What does the vertical arrow in the GATE frame represent?

A

the incidence measure of outcomes

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22
Q

Explain how you can measure indigence of a disease using prevalence measures:

A

We often 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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23
Q

What does the horizontal arrow in the GATE frame represent?

A

represents prevalence measures of outcomes at a point in time.

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24
Q

What is Ratio of Occurrences? (relative risk (RR)) (absolute risk)

A

the exposure group occurrence can be divided by the comparison group occurrence (EGO  CGO) to produce a Ratio of Occurrences;

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25
Q

What is the Difference in Occurrences? (risk difference (RD))

A

the comparison group occurrence can be subtracted from the exposure group occurrence (EGO – CGO) or vice versa ((CGO – EGO) to produce a Difference in Occurrences.

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26
Q

What does it mean when RR=1?

A

when the RR = 1, there is no difference in the effect of E and C on the study outcome; this is often known as the no-effect’ value).

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27
Q

What is Relative Risk Reduction? (RRR)

A

A relative risk that is less than 1.0 can also be expressed as a Relative Risk Reduction (RRR) – because it is reduced below 1.0 (i.e. the no-effect value). The RRR is usually expressed as a percentage and is calculated by subtracting the relative risk from 1.0 and then multiplying by 100.

Relative risk reduction (RRR) = (1 - RR) x 100%. e.g. if RR= 0.6, RRR= (1- 0.6) x 100= 40%

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28
Q

What is Relative Risk Increase? (RRI)

A

if the relative risk is greater than 1.0, it can be expressed as a Relative Risk Increase (RRI). The RRI is usually expressed as a percentage increase, calculated by subtracting 1.0 from the relative risk and then multiplying by 100.

Relative risk increase (RRI) = (RR - 1) x 100%. e.g. if RR= 1.6, RRI= (1.6-1) x 100= 60%

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29
Q

What is RD?

A

Risk Difference

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30
Q

What is RR?

A

Risk Ratio

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31
Q

What is RRI?

A

Relative Risk Increase

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32
Q

What is RRR?

A

Relative Risk reduction

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33
Q

What is OR?

A

Odds ratio

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34
Q

What is the odds ratio? (OR)

A

The odds ratio (OR) is another measure used to compare risks. It is the only estimate of effect that can be derived from case-control studies, although ORs can be calculated in any epidemiological study. The odds ratio is similar to the relative risk in many (probably most) circumstances

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35
Q

What does RD=0 mean?

A

RD = 0 demonstrates no difference in effect of E and C on the study outcome; this is also known as the ‘no-effect value;’

36
Q

What are random errors?

A

Errors caused by chance are described as random errors.

37
Q

What are biases, systematic errors, validity problems or non-random errors?

A

Errors caused by problems with how the study is designed or conducted are described here simply as non-random errors but are often called biases, systematic errors or validity problems.

38
Q

What does the acronym RAMBOMAN show us about epidemiological studies?

A

It demonstrates where non-random errors can occur in epidemiological studies.

39
Q

Define the Setting of study

A

Timing & locations in which eligible population identified (e.g. country/urban/hospital).

40
Q

Define Eligible Population:

A

those from study Setting who meet eligibility (i.e. inclusion / exclusion) criteria.

41
Q

Define Recruitment process

A

How was the eligible population identified from study setting: what kind of list (sampling frame) was used to recruit potential participants: e.g. hospital admission list, electoral rolls, advertisements. Who was recruited? (eg. a random sample, consecutive eligibles)?

42
Q

Define P: Participants

A

recruited from eligibles & allocated to EG/CG. How allocated? By randomisation or by measurement?

43
Q

Define EG

A

participants allocated to the main exposure (or intervention or prognostic group) being studied. If there are multiple exposures, use a new GATE frame for each exposure.

44
Q

Define CG:

A

participants allocated to alternative (or no) exposure (i.e. control).

45
Q

What does ramboman stand for?

A

Recruitment; Allocation; Maintenance; Blind and Objective Measurements of outcomes; and ANalyses

46
Q

What is external validity error? and what type of error is it?

A

One type of recruitment error

is usually described as external validity error because when it is present, the study findings are not applicable (i.e. cannot be applied or generalised) to a wider (or external) population.

This type of recruitment error commonly occurs when the main objective of the study is to measure the characteristics of a specified eligible population (the ‘Eligibles’ in Figure 2.1), but the Participants (P) who are recruited are not representative of the Eligibles.

47
Q

What is random sampling error?

A

When you recruit a non-representative sample just by chance alone, particularly if the sample is small.

48
Q

What is a confounding error?

A

the Exposure Group are recruited from a different source than the participants allocated to the Comparison Group.

and factors of the participants in each group may integer with the effect of the occurrence in study

49
Q

Where in ramboman are cofounders found?

A

allocation

50
Q

What is an RCT?

A

Randomized Control Trial

51
Q

Explain RCTs

A

In RCTs, the study investigators, in effect, flip a coin for each participant.

52
Q

Are RCTs experiments or observational studies

A

Experiments

53
Q

What is the difference between random allocation and random sampling?

A

Studies that randomly allocate participants to exposure and comparison groups should not be confused with studies that randomly sample (recruit) participants from a population in order to identify a representative sample of the population of interest

54
Q

What does it mean when you allocate participants by measurement?

A

Participants are ‘measured’ to determine if they are exposed to the factor(s) being investigated in the study (e.g. they may be questioned about cigarette smoking or be asked to have a blood test). Participants are then allocated to EG (e.g. the smokers group) or CG (the non-smokers group) according to these measurements.

55
Q

Are studies that allocate by measurement considered experimental or observational studies?

A

observational

56
Q

How do you reduce the likelihood of confounding?

A

conduct an RCT in which participants are randomly allocated to EG and CG.

57
Q

What is meant by concealment of allocation?

A

When allocating people into EG and CG an independent person does so, to reduce confounding in some cases. E.g. double blind trial.

58
Q

How can Confounding be reduced in the study?

A

STRATIFIED ANALYSIS

Confounding can be reduced in the study analyses by dividing participants into, say, older and younger age groups or ‘strata’ (equivalent to dividing the study participants in the triangle into two triangles and then analysing the data as if there were two separate studies).

59
Q

Define maintenance error.

A

If some participants’ exposure status changes or some are lost to follow-up, this can introduce a maintenance error.

60
Q

How do you overcome maintenance error?

A

Follow them up every year (or often)

The best way to keep the degree of maintenance error similar EG and CG is to keep the participants and study practitioners ‘blind’ to whether the participant is receiving the study exposure (E) or the comparison exposure (C).

61
Q

How can Measurement of outcomes errors be reduced?

A

Keep the participants ‘blind’ to their EG or CG status

use objective measurements over self-reported or subjective ones.

62
Q

How do you reduce random sampling error?

A

Use a bigger sample

63
Q

How do you reduce random error with objective measurements?

A

Take multiple measurements and take the average

64
Q

What is a CI? (confidence interval)

A

A Confidence Interval describes the range of values of a particular measure derived from a single study (e.g. EGO, CGO, RR, RD, NNT) that is likely to include the true value in the underlying population that the single study recruited participants from.

65
Q

What is the The 95% Confidence interval (CI)?

A

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

or

‘if the same study is repeated many times using random samples recruited from the same total population, then approximately 95% of the (95%) confidence intervals would include the true value in the total population.’

66
Q

Will a 99% CI be larger than a 95% CI?

A

For a given measurement or calculation the 99% CI will be wider than the 95% CI (because there is a 99% chance that it includes the true value rather than only a 95% chance)

67
Q

What does it mean if a sample is statistically significant or not?

A

A study result is considered statistically significant if neither of the confidence limits crosses the no-effect line,

68
Q

What is clinical significance?

A

If the statistically significant data is significant enough for a clinician to implement in practice.

69
Q

What is meta-analysis?

A

combining multiple studies mathematically to reduce the 95%CI and gain a larger sample size, and thus a more accurate result

70
Q

What is an experimental study?

A

Studies in which participants are allocated to EG and CG by the investigators are called experimental studies or experiments.

e.g. RCTs

71
Q

What is an observational study?

A

Studies in which participants are allocated to EG and CG by measurement are usually called observational studies because once the participants are recruited into the study, the investigators measure, or ‘observe’ who is exposed or not

72
Q

What is a longitudinal study?

A

In longitudinal studies, after participants have been allocated to EG and CG, either by the investigators or by measurement, they are followed over time (or longitudinally). The outcomes are usually measured as they occur during the follow up period and incidence can be calculated. It is also possible to measure the prevalence of outcomes in longitudinal studies, at any specified point in time during the follow-up period.

e.g. cohort study and RCTs

73
Q

What is a cross sectional study?

A

In cross-sectional studies participants are allocated to EG and CG, by measurement, at the same point in time that outcomes are measured. The exposures and outcomes are measured cross-sectionally and prevalence can be calculated.

74
Q

What is a prospective study?

A

Measuring Progress

75
Q

Are all RCTs prospective in design?

A

All RCTs are prospective in design because the study always begins by allocating participants to exposure and comparison groups and then ‘exposing’ them or not. So outcomes are always measured after the exposure or comparison exposure has been started.

76
Q

What is a cohort study?

A

Observational longitudinal study

In cohort studies the study investigators measure the presence (and absence) of study exposures among the study participants (also known as a study cohort) and allocate them into the appropriate Exposure Group (EG) or Comparison Group (CG) accordingly (e.g. a smoking group and non-smoking group). Then the participants are followed over time and study Outcomes are counted.

Cohort studies are follow-up studies because the cohort is followed over time to identify study outcomes.

77
Q

What is the difference and similarity between cohort study and RCTs?

A

Both are longitudinal studies
Both use incidence (can use point prevalence)

RCTs are similar to cohort studies except that the participants are randomly allocated to intervention (exposure) or control (comparison) groups rather than being allocated by measurement. Like cohort studies, participants are then followed over time and the study Outcomes are counted.

78
Q

What is the most valid study design for assessing the effectiveness (benefits and harms) of therapeutic or preventive interventions, including screening programmes.

A

RCTs

79
Q

What is a potential flaw in cohort studies?

A

confounding error

80
Q

What is The main advantage of RCTs over standard cohort studies?

A

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

81
Q

What are 2 disadvantages where the RCT design cannot be used?

A

For practical and ethical reasons many important questions cannot be investigated using the RCT design (e.g. assessing the effects of potentially dangerous or illicit drugs).

Moreover when RCTs are possible, they are often conducted in artificial environments and only highly motivated participants might be recruited who may not be representative of usual populations (the R in RAMBOMAN). This may limit the applicability of their findings to populations of interest, although the importance of representativeness is often over-emphasised in appraisals of RCTs.

82
Q

What is The most important causes of bias in RCTs?

A

poor allocation processes (randomisation and concealment) and poor maintenance of participants in their allocated groups.

83
Q

True or false - All cross-sectional studies are OBSERVATIONAL studies

A

TRUE

84
Q

What is ‘Reverse causality’?

A

when the Exposure does NOT cause the Outcome but the Outcome causes the Exposure

85
Q

In what type of study is reverse casualty often found?

A

Cross sectional

86
Q

What is a systematic review (SR)?

A

A systematic review (SR) is a study design that involves searching for and then recruiting a group of studies addressing the same question. The name ‘systematic review’ is used because the studies are ‘recruited’ using a ‘systematic’ or comprehensive search process.

87
Q

What is The Cochrane Collaboration?

A

The Cochrane Collaboration is an international not-for-profit organisation that provides leadership, training, and support for groups involved in undertaking systematic reviews and meta-analyses.

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