Flashcards in Statistics definitions Module 1 Deck (32):

1

## Genotype

### The genetic makeup of a cell, an individual, or an organism

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## Population Stratification

### The presence of a systematic difference in allele frequency between subpopulations in a population, possibly due to different ancestry

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## Penetrance

### Extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it (measured by the proportion of carriers showing the characteristic phenotype)

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## Screening

###
Application of diagnostic tests in patients at high risk for disease, but in whom there is no a priori reason to suspect that disease is present

average risk population

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## Surveillance

###
Repeated application of screening

high risk population

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## Sensitivity

### True positives. Proportion of people with disease who have a positive test

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## Specificity

### True negatives. Proportion of people without the disease who have a negative test

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## Univariate analysis

### One variable is analysed at a time

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## Multivariate analysis

### More than 2 variables are analysed together for any possible association or interaction

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## Hazard ratio

###
A comparison of probabilities of an event in a treatment arm with probabillities of an event in control group

at a given time - set end point

Chance of an event occurring in intervention arm/ Chance of an event occurring in control arm

HR<1 at any particular time less patients in the intervention group are experiencing an event compared to the control group

HR=1 same for both

HR>1 at any particular time more patients in the intervention arm are experiencing an event compared to control group

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## Confidence interval

###
A confidence interval tells you how much uncertainty there is with any particular statistic.

Tells you how confident you can be that the results from a poll or survey reflect what you would expect to find in the entire population.

depends on sample size and variation within the sample

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## Null hypotesis

###
No significant difference between specified populations

(any observed difference being due to chance)

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## Incidence rate

### Number of new cases in a population, per year

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## Prevalence

### Number of cases in a population at a given point in time

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## Mortality rate

### Deaths in a population per time period

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## Standardise rate

###
Adjust numbers to account for variables, by comparing with expected numbers in normal population

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## Odds ratio

### A comparison of the odds of an event after exposure to a risk factor to the odds of an event in a control or reference setting

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## RR

### The relative risk of an event is the likelihood of its occurrence after exposure to a risk variable as compared to the likelihood of its occurrence in a control or reference group

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## Prospective study

###
Selection of cohorts and measurement of exposures or risk factors before the outcome has occurred

Advantages: high quality, can accomodate for novelty

Disadvantages: expensive and time consuming

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## Retrospective

###
Looks backwards at risk factors or exposures that have already led to a specific outcome.

Advantages: Fast and inexpensive

Disadvantages: rely on accurate record keeping, unmeasured confounders might be present

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## NPV

###
Probabitly that negative test result does not have the disease

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## PPV

### Probability that positive test result truly has the disease

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## P value

###
proballity of calculating a difference when there really isnt one - p values smaller than significance level allow you to reject your null hypothesis

p=0.05 gives significance levels of 95% , 95% sure that the difference is not due to chance

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## ITT

###
Once patients are randomised, analysis includes every patient regardless of non-comliance or dropout

avoids overoptimistic estimates

but dilute effect of intervention as including those that didn't go according to plan

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## per protocol

###
only analyses patients that have completed the protocol

limitations: results in ideal patient, not real world

can introduce confounders by including patients were randomised, what caused them to withdraw?

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## Cofidence level 95%

### inverse of p value

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## Cross sectional study

###
analyse data collected at a specific point in time

advantages: routine data collection so very little expense

disadvantages: open to confounding factors

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## case control

###
Compare cases with disease and controls with disease and look retrospectively at exposures

advantages: cost effective and quick

disadvantages: selection bias, corelation not caussation

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## cohort study

###
compare exposure and non exposure ove rtime, to see who will develop a specific outcome

advanatages: can measure mltiple outcomes

disadvanateges: correlation, not causation

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## RCT

###
experiment that introduces treatment/exposure and then measures effect - gold standars for measuring treatment effect

advantages: randomisation minimises selction bias and confounding factors

Disadvantages: expensive, time consuming

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## Systematic review

###
critical assessment and evaluation of all research studies addressing a particular issue

advanatges: quick cheap minimise bias

disadvantages: selction bias can be low quality

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