Critical numbers Flashcards by Emily Green

What is prevalence probability?

Probability of having a disease at a given point in time

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Incidence probability

Probability of getting a disease during a specified point in time

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Incidence rate

average rate of change over time

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Hazard rate

Instantaneous rate of change

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Incidence

Number of people newly diagnosed

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Prevalence

new and pre-existing cases

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Probability equation

P = no. of case/ total population

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Odds equation

odds = cases/non-cases

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Absolute risk definition

Difference between 2 risks

e.g. 4 in 100 risk of non-smokers developing a disease

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Relative risk definition

Ratio between 2 risk

e.g. risk of getting a disease is increased for smokers

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What are the 4 different observational studies?

1) Cross-sectional
2) Case-control
3) Cohort
4) Ecological

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What is a cross-sectional study?

Observations made at a specific point in time (now)

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Strengths and weaknesses of a cross sectional study?

Strengths

Fast, inexpensive
who currently has exposure and outcome
no follow up

Weaknesses

not suitable for rare diseases
difficult to establish order of events
Can’t find causes

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What is a case control study?

(Past) select participants with and without outcome and look back to see who had exposure

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Strengths and weaknesses of case control study?

Strengths

suitable for rare diseases
multiple exposures can be studied
quick

Weaknesses

only a single disease can be studied
difficult to establish order of events
affected by selection bias & confounding factors

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What is a cohort study?

(future)
collect participants info on a sample (some have exposure, others don’t)
Follow up over time, see who gets outcome

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Strengths and weaknesses of cohort study?

Strengths

useful for demonstrating causal effect
multiple diseases & exposure can be studied
less chance of bias

weaknesses

time consuming and expensive
not suitable for rare diseases
people drop out

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What are the 2 experimental studies?

Randomised control trial and crossover

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What is an RCT? Pros and cons?

Participants randomised to groups and followed up to compare outcomes
Strengths
- 'gold standard'
- prevents bias - can be double blinded
- shows cause and effect
Weaknesses
- expensive
- not suitable for long term effects
- not always ethical 
can be effected by non-compliance

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What is a crossover trial? pros and cons?

Everyone in the study has all arms of the trial at some point

order of each arm randomised
everyone is their own comparison

Cons

more technical analysis
not always suitable (if drug/ surgery has carry over effects)

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Association vs causation

Association = a statistical link between exposure and disease

Causation = a statistical link where a disease is directly caused by the exposure

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What is simple random sampling?

Each member of the population has an equal probability of being selected

computer generated
not always good representation
not precise

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What is systematic random sampling?

Members of the population are selected at equal intervals

cons

need complete list of population
large standard error
periodicity patterns>characteristics that occur at intervals

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What is stratified random sampling?

population is split into groups and samples are taken from each group 
Pros
- increases representation
- smaller standard error
cons
- requires prior info about population
- expensive

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What is cluster sampling?

Population is partitioned into clusters and a sample of clusters is selected (clusters similar) - complete list of population not needed - cheaper cons - clustering decreases statistical precision (higher standard error)

Standard deviation vs standard error

``` SD = within a sample SE = between samples ```

P -value

p < 0.05 indicates statistical significance

Crude vs adjusted effects

Crude = does not take into account confounding variables Adjusted = accounts for confounding factors

Biochemical, chemical or hormonal stress?

Metabolic changes due to stress | - endorphin levels altered

Signs of physiological stress?

Physiological signs of stress - shallow breathing - raised blood pressure - increase in acid production in the stomach

Signs of emotional stress?

Emotional signs of stress: - mood swings - tearful - irritable - aggressive - apathetic

Cognitive stress signs?

- Negative thoughts | - loss of concentration

Behavioural signs of stress?

- Increases absenteeism - smoking - alcohol consumption - change in food consumption - sleep disturbances

What are the two types of emotional responses to stress?

Positive affect | Negative affect

Social signs of stress?

Similar to behavioural - social relationships - participation in activites/work

What is primary prevention?

prevention of disease in people who have not been diagnosed as having the disease, includes health promotion

What is secondary prevention?

Early detection of disease | - followed by appropriate intervention

What is the high risk approach to prevention?

targeting of health promotion and disease prevention at groups based on info from epidemiological studies

What is the population approach to prevention?

Aims to lower the level of risk in the population, includes health promotion

What is tertiary prevention?

Aims to reduce the impact of the disease and promotes quality of life through active rehabilitation

What is the preventing paradox?

A preventive measure which brings much benefit to the population, may offer little to each participating individual

What aspect of the relationship between occupation and asthma could only be examined through prospective studies? a. Association b. causation c. analytical d. descriptive e. Qualitative

B Causation: the existence of a causal relationship between variables; the cause must precede the effect

What is an ecological study?

Uses routine date from populations | - looks at prevalence, trends and correlations

What is a longitudinal study?

Observational study of persons over a period of time taking measurements at more than one time point

What does it mean if there is a big difference between mean and median?

It is not normally distributed

If a study is not normally distributed which data should you use? (e.g. mean, median, SD, SE, IQR)

Median

What analytical value do you pair with median?

IQR | mean and SD

Which of the following is incorrect? The standard error of the mean of a sample: a. Can be calculated using the standard deviation and the size of the sample b. Measures how far the sample mean is likely to be from the population mean c. Is used in the calculation of a confidence interval d. Is greater than the standard deviation of the observations e. Should only be calculated when the sample is normally distributed

D. The SE will be smaller than the SD

What is linear regression?

Models the dependency of Y with a change in X - can have positive, negative or no correlation - can remove background association to reveal a clearer picture of the relationship between the main exposure of interest and outcome

What is multi-variable regression?

Adjust for all the variables in the model

What is opportunity cost?

To spend resources on one activity means a sacrifice in terms of a lost opportunity cost elsewhere

What is economic efficiency?

It is achieved when resources are allocated between activities in such a way as to maximise benefit.

What is QALYs?

Quality Adjusted Life Year | - combines length of life with quality of life

What are the 4 types of economic evaluation?

``` 1) Cost effectiveness analysis (measure in natural units e.g. change in BP) 2) Cost-utility analysis (measured in QALYs) 3) Cost-benefit analysis (measure in monetary units) 4) Cost-minimisation analysis ```

Cost effectiveness ratio?

Difference in costs/difference in benefits

What is observer bias?

When variables are reported differently between assessors

What is selection bias?

error in the process of selecting participants for the study and assigning them to particular arms of the study

What is measurement bias?

When information is recorded in a distorted manner (inaccurate tool)

What is procedure bias?

Subjects in different arms of the study are treated differently

What is Misclassification bias?

Occurs when a variable is classified incorrectly

Critical numbers Flashcards

(60 cards)