Flashcards in Session 2 Deck (25)
What is a sample average?
Same as the mean of a sample
How do sample means usually look?
All look similar regardless of population
What is the average of the means of the sample?
Mean of the population values
What is the distribution of the means of samples?
Normal Gaussian distribution
What is a confidence interval?
95% confidence interval contains the mean of the population values 95% of the time
What is the purpose of statistics?
To generalise and infer about a population
What is a sample
As a representative as possible of the population
What happens if there is a wider 95% confidence interval?
Greater variation in population values
Smaller the size of the sample used to calculate
What is precision?
Exact and accurate
What is bias?
Of or on a target
Something has no bias- on a target
What is selection bias?
Errors due to systematic differences in the ways in which the two groups were collected
What is information bias?
Errors due to systematic misclassification of subjects in the group
Differential recall errors especially in case control studies
Differential observer or interviewer errors
Differential measurement error
Give a confounding factor example
Distort results and give misleading results
E.g. People in Bournemouth have higher levels of cancer but age is a confounding factors as older people are more likely to have cancer but also more likely to live in Bournemouth
What is prevalence?
Incidence x duration of disease
The amount of people who currently have the disease
What is Incidence?
Number of new cases of the disease per 1000 people per year
What is a cohort study?
Recruiting disease free individuals and classifying them according to their exposure status, they are then followed up for extending periods and disease progress and Incidence rate is calculated
What is a case-control study?
Recruiting disease free individuals and diseased individuals and then there exposure status is then determined
What is a confounding factor?
Something that is associated with both the outcome and the exposure of interest but is not on the casual pathway between exposure and outcome
Why are Case control studies heavily bias?
Selection bias- not representing the general population
Recall bias- exposure status incorrectly determined as looking back at history
What is risk ratio?
Ratio of prevalence portions of outcome in groups defined by levels of exposure at a particular time
What is rate ratio?
Ratio of incidence rates of outcome in groups defined by levels of exposure after a particular time period
What is odds ratio?
Ratio of odds of outcome in groups defined by levels of exposure at a particular time
What is a cross section survey used for?
Analysed to give prevalence
What can be calculated from a cohort study?
Incidence rate ratio