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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
Differential mis-classification


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?

Risk ratio
Incidence rate ratio
Odds ratio


What can be calculated from a control study?

Odds ratio