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Epidemiology > Second midterm content > Flashcards

Second midterm content Flashcards

1
Q

descriptive statistics vs inferential statistics

A

descriptive: used to describe the main features of a data set
inferential: used to draw conclusions and involve making inferences about the larger group from a smaller subset

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2
Q

measures of tendency vs measures of dispersion

A

tendency: mean, median and mode
dispersion: range. interquartile range and standard deviation

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3
Q

what is the central limit theorem

A

sampled means will tend to be normally distributed given that we took enough samples
- even If the data itself id not normal the CLT tells us that the distribution of the sampled means will be

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4
Q

what is a P value

A

the probability of obtaining the observed results assuming the null hypothesis is true
- if the p-value is less than the alpha value, the result is statistically significant

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5
Q

what is a T-test

A
  • compares the means of 2 groups
  • used when you have a continuous variable
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6
Q

what is an ANOVA test

A
  • compares the means of 3 or more groups
  • used when you have a continuous variable
  • won’t tell you which groups are different but will tell any of the groups are significantly different
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7
Q

what is a chi-squared test

A
  • determines if there is a relationship between 2 categorical variables
  • use when you are dealing with types of groups and want to know is one category is related to another
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8
Q

what is a Pearson correlation test

A
  • assesses the association between 2 continuous variables
  • use wan you want to determine the direction and strength of a relationship between 2 continuous variables
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9
Q

what is regression

A

shows how much the dependent variable will change when the independent variable is changed

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10
Q

types of regression

A

linear regression: models outcomes of continuous variables
polynomial regression: measures continuous variables with a non-linear relationship
logistic regression: model binary outcomes (either yes or no)

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11
Q

what is multiple linear regression

A

when the outcome is dependent on more than one variable

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12
Q

what do the measures of association and measures of effect measure

A

MoA: the ratio of 2 measures of disease frequency - null value is 1
MoE: the difference between 2 measures of disease frequency - null value is 0

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13
Q

what are the measures of association

A

risk ratio
odds ratio
incidence rate ratio

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14
Q

what are the measure of effect

A

risk difference
attributable proportion (exposed)
population attributable risk
population attributable fraction

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15
Q

what is risk ratio

A

compares the risk of getting disease in the exposed and not exposed group

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16
Q

what is odds ratio

A

measures the odds that an outcome will occur if exposed, compared to the odds of the outcome occurring if not exposed

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17
Q

confidence interval for measures of association

A

if the confidence interval includes 1 the association is not statistically significant

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18
Q

what is incidence rate ratio

A

the ratio of disease incident rate in the exposed group vs in the non-exposed group

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19
Q

what are person-time years

A

allows you to account for the individual time that each participant contributes

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20
Q

interpreting MoA

A

range = 0 to infinity
MoA = 1 means risk/odds/rate in exposed is equal to non exposed
MoA > 1 means greater in exposed individuals
MoA < 1 means less in exposed individuals

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21
Q

what is the case for risk ratio and odds ratio in rare diseases

A

RR ~ OR because a and c values are so small

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22
Q

what are measures of effect useful for

A

knowing how much disease could be eliminated by removing the exposure

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23
Q

what are measures of association useful for

A

investigating causation

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24
Q

what is baseline risk

A

disease in the non-exposed group OR amount of disease present not due to the exposure

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25
Q

what do measures of effect tell us about exposed groups

A

how mush od the total risk of disease is actually due to the exposure of interest

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26
Q

what is risk/rate difference

A

the difference in risk or rate of the outcome in the exposed and non-exposed groups

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27
Q

interpretation of risk/rate difference

A

the excess risk of getting disease due to exposure is…

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28
Q

what is excess risk

A

extra risk beyond the baseline risk

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29
Q

what is attributable proportion

A

the proportion of risk/rate of the outcome in the exposed group that is due to the exposure

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30
Q

interpretation of attributable proportion

A

…% of disease in the exposure group is due to the exposure

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31
Q

measures of effects in exposed groups vs in population

A

exposed groups: risk difference and attributable proportion
populations: population attributable risk, population attributable fraction

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32
Q

what is population attributable risk

A

the amount of disease in the entire population that is due to the exposure

prevalence of disease in population - baseline level of disease

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33
Q

interpreting MoE

A

range = -infinity to infinity
MoE = 0: exposure has no effect
MoE > 0: exposure positively associated with disease
MoE < 0: exposure negatively associated with disease
- null value is 0 because it is a difference not a ratio

34
Q

population attributable fraction

A

proportion of disease in the entire population that is due to the exposure

PAR/prevalence of disease in population

35
Q

interpreting population attributable fraction

A

…% of disease in the population could be eliminated if the exposure was removed

36
Q

interpreting population attributable risk

A

the excess risk of disease in the population that is due to the exposure is…%

37
Q

inductive vs deductive research

A

inductive: observations
deductive: intervening

38
Q

what is quantitative research

A
  • objective
  • one truth
  • observer doesn’t influence findings
  • facts separated from values
39
Q

what is qualitative reasearch

A
  • subjective
  • truth is subjective perception of findings
  • findings are mutually created between observer and subject
  • value lead
40
Q

types of qualitative research methods

A

interview
focus group
ethnographic research
case study research
record keeping
qualitative observation

41
Q

types of descriptive studies

A

case reports
case series
surveys

42
Q

analytical vs descriptive studies

A

descriptive
- provide information about occurrence of disease without investigating associations
- generate hypothesis
analytical
- establish relationships between risk factors and the occurrence of disease, make comparisons between groups
- hypothesis testing

43
Q

types of analytical studies

A

observational studies
experimental studies

44
Q

what is an observational study

A

researcher has NO control over subjects being compared
exposed subjects already exist

45
Q

what is an experimental study

A

researcher randomly allocates subjects to the groups being compared and intervened (adds exposure)

46
Q

when would you choose an observational study over an experimental study

A

if exposure of interest is harmful
if it is expensive to administer exposure
if the exposure is hard to control

47
Q

types of observational studies

A

cross-sectional
cohort
case-control

48
Q

what is a cross-sectional study

A
  • select participants without regard to exposure or outcome status
  • then measure the exposure and outcome at the same time (a snapshot)
49
Q

objective of cross-sectional studies

A

to estimate prevalence - how many subjects have exposure and how many have outcome?

50
Q

prevalence vs incidence

A

prevalence: new and old cases (have the outcome)
incidence: new cases (get the outcome)

51
Q

why can we only measure prevalence and not incidence in cross-sectional studies

A
  • because we cannot establish temporality since we determine E and O at the same time
  • exception = longitudinal studies
52
Q

what are longitudinal studies (cross-sectional)

A

the same individuals are measured more than once, allows to establish incidence

53
Q

advantages of cross-sectional studies

A
  • determine prevalence of E and O
  • study multiple exposures and multiple outcomes
  • good for studying permanent factors
  • no loss-to-follow up selection bias
  • less potential for bias than case-control studies
  • can measure ALL MoA and MoE EXCEPT for rate
54
Q

disadvantages of cross-sectional studies

A
  • not good for rare E, rare O or short duration diseases
  • doesn’t measure incidence, ant establish temporal sequence
  • selection, information and confounding bias
55
Q

what is a cohort study

A

select participants based on exposure status

56
Q

what is a cohort

A

a group of subjects that has a defined characteristic in common - exposure status

57
Q

general design of cohort studies

A
  • choose a group of disease free individuals
  • classify them based on exposure
  • follow over a time period
  • compare the development of disease in E+ and E- group
58
Q

retrospective vs prospective cohort studies

A

retrospective: establish from past records and follow-up to present day or more past records
proscpective: start from present day and follow into the future

59
Q

Analysis in cohort studies

A
  • measures incidence (new cases)
  • can use ALL MoE and MoA
60
Q

advantages of cohort studies

A
  • good for rare exposures
  • study several outcomes
  • temporal sequence established in prospective studies
  • provides incidence data
  • no recall-bias with prospective studies
61
Q

disadvantages of cohort studies

A
  • bad for rare outcomes
  • can study only one or a few exposures
  • selection, information and confounding bias
  • expensive and time consuming
  • can have long follow up time: loss to follow-up is a major concern and non-response bias
62
Q

addressing confounding bias in cohort studies

A

exclusion/restriction: subjects have same level of major CFV
matching: E- have same CFVs as E+
analytical citron: control for CFVs with stratification or multivariable regression

63
Q

ways to ensure validity in in cohort studies

A
  • selection of E+ and E- groups
  • follow-up of cohorts
  • objective diagnosis of disease status
64
Q

how can we have more than 2 exposure groups in cohort studies

A

can have multiple E- groups or E+ groups with different levels of exposure

65
Q

what is the biggest challenge in cohort studies

A

follow-up

66
Q

what is a case control study

A

choose participants based on their disease status

67
Q

what are cases and what are controls

A

cases: have the disease/outcome of interest
controls: do not have the disease/outcome of interest
- selection occurs at this level
- determine who was exposed and who wasn’t in both groups

68
Q

why are case-control studies always retrospective

A

cases have already occurred do we must trace back if they were exposed or not

69
Q

analysis of case-control studies

A

compare proportion of exposure in the cases with that in the controls
- CANNOT calculate incidence/risk therefore NO RR, but can still calculate OR

70
Q

advantages of case-control studies

A
  • fast and inexpensive (because retrospective)
  • best for investigating source of an outbreak
  • good for rare diseases/outcomes
  • good for multiple risk factors for a single disease
71
Q

disadvantages of case-control studies

A
  • CAN’T calculate disease incidence or prevalence
  • can only study one outcome
  • study design most prone to all biases
  • bad for rare exposure
  • temporal relationship is an issue if using prevalent cases
72
Q

what is a study base (case-control studies)

A

the population from which cases (and controls) are obtained
primary study base: the population from which the cases arise can be easily defined
secondary study base: one or more steps removed from the primary population

73
Q

control selection from a secondary study base

A
  • controls should be randomly selected from non-cases in the registry
  • those controls should be selected from diagnostic categories not associated with the exposure of interest
74
Q

use of multiple controls in a case-control study

A

controls come from different sourced e.g. hospital and neighbourhood controls

75
Q

why can’t we calculate risk/rate ratio in case-control studies

A

because we set the risk of our disease by selecting participants based on their disease status
- must use OR to estimate RR because OR ~RR for rare diseases

76
Q

factors for evaluating studies (critical appraisal)

A

Methodological: study design, statistical analysis, addressing bias
Non-methodological: relevance, originality, conflicts or interest

77
Q

how to estimate PAF and AP in case-control studies

A

AP = (OR-1)/OR
PAF

78
Q

Recall bias in case-control studies

A
  • big problem if accuracy differs between cases and controls
  • retrospective so need to ask people about their past
79
Q

how to ensure validity in case-control studies

A
  • proper selection of cases and controls, to boost power can pick 4:1 controls:cases
  • ensure comparability
  • unbiased history of exposure to the factor of interest
  • control for confounding
80
Q

what is critical appraisal

A

a systematic process used to identify the strengths and weaknesses of a research article in order to assess the usefulness and validity of research findings
- lacks a “gold standard”

81
Q

questions asked in critical appraisal (10)

A

relevance?
adds something new?
what is the research question?
appropriate study design?
addresses bias?
performed as per methods stated?
hypothesis stated?
appropriate stats used?
justified conclusions?
conflicts of interest?

82
Q

what is the difference between the 3 types of observational studies

A

the way that participants are selected

Epidemiology (3 decks)

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