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POPH192 > module 5 & 6 flash cards > Flashcards

module 5 & 6 flash cards

1
Q

what are the three things that need to be considered for internal validity?

A

bias, chance and confounding

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2
Q

what is one way you can easily reduce chance

A

by increasing the sample size

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3
Q

what does increasing sample size do for chance

A

can reduce variability between samples
can increase likelihood of getting a sample that is representative of the population
can increase precision of parametre estimate

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4
Q

what is a fundamental concept of chance

A

you cannot eliminate sampling error but it can be reduced with larger sampling sizes.

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5
Q

what are type II errors in chance?

A

you incorrectly fail to reject the null hypothesis when you should have (the p value shouldve been less than 0.05 but we got one that was more than 0.05)

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6
Q

what are type I errors?

A

when you incorrectly find an association when there isnt actually one.

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7
Q

if your 95% confidence interval contains the null value is it statistically significant?

A

no, if it does the p value will also lie in the interval so the association wont be statistically significant.

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8
Q

what are three reasons why p values are problematic?

A

arbitrary threshold - always report what the number of the p value is not just if its significant or not.
Only about null hypothesis-
nothing about importance- statistical significance is not clinical significance.

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9
Q

what stages of the design study process can bias be controlled for?

A

can only be controlled in the design and data collection stages

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10
Q

what is selection bias

A

when there are differences between people who are included in the study and those who are not.

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11
Q

what three things do you need to take into consideration of selection bias for case control studies

A

who does it affect (what group), how does it affect them (over/under representated), what does this do to the measure of association (biased upwards or downwards)

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12
Q

how can selection bias occur in cohort studies

A

loss to follow up
If comparision is selected seperately from the exposed group this can lead to bias.

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13
Q

what is information bias?

A

bias that is created through differences in the way data on exposed or outcome are obtained.

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14
Q

what is publication bias?

A

authors encouraging organisations to approve things containing ‘positive’ findings

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15
Q

what are the three properties of a potential confounder?

A

needs to be independently associated with both the outcome and exposure
not on the causal pathway .

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16
Q

what four things can confounding do ?

A

overestimate of a true association
underestimate a true association
change the direction of a true association
give an apperance of an association when there isnt one.

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17
Q

what are three methods of controlling for confounding during the study design

A

randomisation
restriction
matching

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18
Q

what is randomisation, where can it be applied and what three factors does it require?

A

can only be applied in randomised control trials and it is where people are randomly allocated into their groups. a strength of this is that it controls for known and unknown confounders.
randomisaton requires:
-a large sample size
-need equipose
- an intention to treat analysis

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19
Q

what is restriction, where can it be applied and what are its cons?

A

restriction the sample to one stratrum of potential confounder (ie restrict the study to only look at particular age brackets) and this method can be applied to all study types.
but this can…
-reduce generalisiability
-reduces the number of people who could participate
-potential for resididual confounding with incorrectley measured confounders.
-usually only one potential confounder

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20
Q

what is matching, where can it be applied, pros and cons

A

you choose people to have the same composition in both the control and comparison groups in regards to potential confounder. can do this at individual level or at frequency level (ie 20% simularity). useful for difficult confounders, can improve efficiency of case control studies
but
-difficult and limit potential participants
-need special matched analysis

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21
Q

what are three methods for controlling confounding in the study analysis?

A

stratification
multivariable analysis
standardisation

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22
Q

what is stratification and what are the pros and cons

A

calculating the measure of association of each stratum of potential confounders- you can compare the values and see if there is a difference between the
pros
easy for small number of potention confounders with limited strata
evaluate the impact of confounding
can identify effect modification

cons
- can leave residual confounding
- not feasible when dealing with lots of potential confounders with lots of strata.

23
Q

what is multivariable analysis

A

method where multiple potential confouders are controlled.
this is benefical as it can work in situations where stratification doesnt work (controlling for lots of different confounders at once).

24
Q

how does effect modification differ from confounding?

A

effect modification is when the stratum specific relative risks are different, can see whether an effect modifyer had an impact on the causal pathway.

24
Q

what is standardisation

A

age structures differ and disease risk differs by age.

25
Q

what is the causal pie model?

A

where multiple exposures as sufficient to cause the outcome to occur.

26
Q

what are the guidelines of causability?

A

BESTCDS
1- biological plausability
2- experimental evidence
3- specificity
4-temporal sequencing
5- consistency
6- dose-response relationship
7- strength of associaton

27
Q

what are the two main types of reviews?

A

narrative (may be heavily influenced by opinion) and systematic (replicable, transparent and systematic

28
Q

why are systematic reviews done?

A

collate evidence and sythesise their results
if theyre done well they reduce bias that may be encountered with narrative reviews.

29
Q

what is heterogeneity?

A

when something varies across different groups its heterogenous

30
Q

what is homogeneity?

A

when something is consistent across different groups

31
Q

what are the three levels of prevention against disease/harm etc?

A

primary- attempting to prevent the disease from occuring ie immunisation
secondary- reducing the impact of the disease, shortening duration, weakening severity eg early diagnoses or treatment
tertiary-reduce the impact or number of complications from it. eg rehibilitaton units.

32
Q

what are the two strategies for primary prevention

A

high risk strategy- where you target preventitive processes to people that are at high risk of the disease
population mass- aim to reduce health risk of the whole population.

33
Q

what is the prevention paradox?

A

a pretentative measure that brings large benefit to the community may offer little to each participating individual

34
Q

what is evidence based practice? what are the three intersecting factors for it?

A

research provides the evidence to guide your practice
-patients values and choices
-clinal expertise
-best avaliable evidence

35
Q

what are the 5 elements of health survellience?

A

data collection- analysis- interpretation- dissemination- action (these repeat)

36
Q

what is indicator based survelliance
what are three types of indicator based?

A

selected indicators that are under survellience
passive, active and sentinel survellience

37
Q

what is passive survelliance ?

A

routine reporting of health data
ie notifiable diseases, disease regestries and hospital data

38
Q

what is an example of active survelliance?

A

the health survey

39
Q

what is sentinel surveillance

A

selected institutions or groups that contribute to the health data to monitor disease or trends and detect outbreaks

40
Q

what are some characteristics of a good surveillance system?

A

clear case definiton
organised
practical and simple
uniform

41
Q

what is screening

A

the widespread use of a simple test for a disease in a seemlingly healthy individual

42
Q

what is a screening test

A

a test to discover suspected individuals who go on to have further diagnoses tests to determine the diagnoses.

43
Q

what does sensitivity tell you and what is its formula

A

proportion of people with the disease who test positive
a/a+c

44
Q

what does specificity tell you and what is its formula?

A

proportion of people without the disease who test negative
b/b+d

45
Q

what does a positive predictive value tell you and what is its formula

A

what proportion of people test positive and have the disease
a/a+b

46
Q

what does negative predictive value tell you and what is its formula?

A

what proportion of people test negative and actually dont have the disease
d/c+d

47
Q

what are three things that screening tests need to be in order to be effective

A

safe, simple and cheap
if they werent these things then people would be less likely to go and get the screening tests which would result in greater irreverisble disease impacts in the population.

48
Q

what does the solid veritical line on a forest plot mean?

A

the null value

49
Q

what does the solid squares mean on a forest plot?

A

shows the weighting of that statistical analysis has given. bigger square= more weighting

50
Q

what does the diamond on a forest plot indicate?

A

the overall pooled measure of association from the studies, the centre of the diamond is the overall point estimate with the width of the diamond being the confidence interval.

51
Q

why would we rely on the findings of a systematic review over one very good randomised control trial?

A

Because a systematic review collects information fro a large amount of avaliable reasearch then it summarise, appraise and communicate the results.

52
Q

what are the main types of outbreaks?

A

common source (point, continous, intermittent)
propigation (person to person)
mixed (starts as common then passed on person to person)

POPH192 (4 decks)

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