Public Health Flashcards by Karen Tan

What are the different kinds of research questions?

Descriptive and analytical

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What are the characteristics of non-longitudinal studies?

No follow up of subjects. Includes ecological, cross-sectional and case control studies

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What are characteristics of longitudinal studies?

Follow up of subjects, information progressively collected over a period of time

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What is prevalence?

Number of existing cases of an outcome in a defined population at one point in time. Expressed as proportion or percentage

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What is incidence?

Number of new cases of an outcome in a defined population during a time interval. Expressed as a rate, and can only be determined from a longitudinal study

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What is risk?

Probability of disease occurring during a time period.

risk=n/P per time

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What is rate?

Probability of disease occurring during sum of individual follow-up periods

rate=n/(total person-time of follow-up)

Considers how long each person was in the study

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What is hazard?

An instantaneous rate derived from longitudinal studies

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What is relative risk/rate?

Relative magnitude of change in risk/rate of outcome, associated with exposure

RR=R(e)/R(u)

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What is attributable risk/rate?

Absolute magnitude of change in risk/rate of outcome, associated with exposure

AR=R(e)-R(u)

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What is the attributable risk/rate percent?

Proportion of outcome among those exposed, that is related to the exposure and not some other factor

AR as a proportion of those exposed

AR%=AR/R(e)100%=[R(e)-R(u)]/R(e)100%

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What is the population attributable risk?

The additional risk/rate of the outcome in the whole population that is due to the exposure

PAR=R(t)-R(u)

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What is the population attributable risk percent?

The proportion of the outcome in the whole population that is due to the exposure. Also known as preventable fraction

PAR%=PAR/R(t)100%=[R(t)-R(u)]/R(t)100%

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What are the Bradford Hill Criteria for Causality?

Temporal relationship, Strength, Dose-response relationship, Consistency, Plausibility, Exclude alternative, Experimental evidence, Specificity, Coherence

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Describe cross-sectional studies

Take a cross section of the population and obtain information from them.

Tends to be descriptive
Non-longitudinal
Relatively cheap & easy
Weak evidence of causality

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Describe case control studies

Recruit subjects with an outcome, and then match them with controls without that outcome by confounders. Compare previous exposures between these subjects.

Useful for studying rare outcomes
Non-longitudinal
Can calculate odds ratio

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What is an odds ratio?

An approximation of relative risk

OR=[outcome(exposure):outcome(non-exposure)]/[no outcome(exposure):no outcome(non-exposure)]

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Describe cohort studies

Follows a population without an outcome, to determine who then develops that outcome

Restrospective cohort studies only begin following subjects after an outcome, and look back to consider the exposure

Longitudinal - can collect incidence
Can consider multiple outcomes and exposures
Difficult to study rare outsomes
Expensive

Describe selection bias

A systematic difference in the people recruited to participate in a study compared to the general population, meaning that the observed result may not reflect the true situation

A systematic difference between the groups being compared. Can be due to the way groups are assigned, due to drop out

How can selection bias be reduced?

Maximise response
Minimise lost to follow-up
Intention-to-treat analysis
Randomisation of study groups

Describe information bias

Systematic difference in the way information is collected between compared study groups

How can information bias be reduced?

Make sure collection methods are uniform

Objective assessment
Standardised tools
Blinding

What is a confounder?

A factor that mediates the relationship between an exposure and an outcome of interest, such that the association between the two is distorted. This confounding factor independently predicts the outcome, and is not in the causal pathway between the two.

Describe clinical trials

Longitudinal studies to determine if an intervention vs placebo has an effect on an outcome.

How can confounding be reduced?

Randomisation of study groups

How can randomisation be used in a clinical trial?

All subjects are randomly placed into treatment groups so that every treatment group is made up of the same kind of people. This should distribute confounders evenly into all groups, even for confounders that we are unaware of The effectiveness of randomisation can be assessed by profiling the treatment groups and considering their similarity

How can blinding be used in a clinical trial?

Ensure that neither subjects nor investigators are aware of which treatment subjects are receiving. If there are independent assessors of outcomes, they should also be blinded.

How can cross over in clinical trials lead to selection bias?

Subjects who cross over tend to be systematically similar, and thus it is a source of self selection

How does intention-to-treat analysis reduce function?

FIND SOME KIND OF EXPLANATION

What is hazard/hazard rate?

An instantaneous rate derived from a longitudinal study with close follow up.

What is hazard ratio?

A measurement similar to risk ratio that applies to the whole period of follow-up.

What is the number needed to treat?

Number of people needed to undergo the treatment in order to prevent the outcome in just one of those people. It is a marker for the efficiency of the intervention. It is affected by RR as well as the underlying likelihood of the outcome. NNT=1/(AR)

What is the purpose of PICOT?

PICOT is used to frame a research question

What does PICOT stand for?

Population, Intervention, Comparator, Outcome, Timing

What is internal validity?

The extent to which the results of a study are valid for the patients who were studied

What does internal validity depend upon?

Appropriate study design, data collection and data analyses. Whether the study appropriately controlled for bias and confounding ``` Consider: Randomisation Blinding Objective Outcome Assessment Intention-to-treat Analysis ```

What is stratified randomisation?

A way to ensure that key confounders are spread across treatment groups evenly, and so further reduce the potential for confounding effects

What does the p-value indicate?

The probability that the results observed arose by chance

What is the confidence interval?

The interval in which there is a 95% confidence of the true value lying The width of the CI also indicates precision of the result.

What p-value and confidence intervals are considered significant?

p<0.05 | CI not spanning the null value

What is the null value?

The value that indicates no differences between the groups being compared. When the comparison is a ratio, the null value is 1. When the comparison is an absolute difference, the null value is 0

What is external validity?

Whether an internally valid study is abled to be applied to a certain patient or situation

How does one consider whether a study is externally valid?

Assess similarity via PICOT