Statistics Flashcards
Define sampling
The selection of a subset of individuals from within a statistical population
What is sampling bias?
Where some individuals are more likely than others to be included in the study
What is recall bias?
When individuals cannot remember specifics
What is social-desirability bias?
When individuals tell us incorrect information because they feel a societal pressure
What is a confounding factor?
Something that is related to the outcome and the characteristics of interest
What is a case control study?
- Take a sample of individuals with outcome, and similar group without
- Look back retrospectively to see who had exposure
What are the advantages and disadvantages of a case control study?
+ Good for investigating rare outcomes
+ Relatively cheap and quick
- Subject to recall bias
- Can only investigate a single disease
What is a cross sectional study?
Look at what is happening now (snapshot of time)
What are the advantages and disadvantages of a cross sectional study?
+ Very cheap, quick and easy
- No time scale
- Not suitable for rare diseases
What is a cohort study?
- Collect information on a sample without the outcome
2. Follow up over time, looking at exposure, to see who gets the outcome
What are the advantages and disadvantages of a cohort study?
+ Can look at a variety of outcomes
- Time consuming and expensive
- Not great for rare outcomes or outcomes that take a lot of time to develop
What is a randomised control trial?
- Have multiple (at least two groups ) referred to as arms
- Give different exposures to each arm
- Compare outcomes
.What are the advantages and disadvantages of RCTs?
+ Minimises bias and confounding factors and has statistical reliability
+ Comparative study design
- Not always suitable, there can be ethical issues
- Expensive
What is the equation for proportion / probability?
Event / Total
What is the equation for odds?
Event / Non event
What is the equation for absolute risk difference?
Probability - Probability
What is the equation for risk ratio?
Probability / Probability
Focus group goes on top
What is the equation for odds ratio?
Odds / Odds
Focus group goes on top
What is negative skew?
Where the median is greater than the mean
What is positive skew?
When the median is less than the mean
What data would be best to publish for a normal distribution?
Mean and standard deviation
What data would be best to publish for a non symmetric, skewed distribution?
Median and IQR
In normally distributed data, what percent of data lies within 1 SD of the mean?
Approx 68%
In normally distributed data, what percent of data lies within 1.96 SD of the mean?
95%
What would a Pearson’s correlation of 1, 0 and -1 mean?
1 = Perfect positive linear association 0 = No linear relation -1 = Perfect negative linear association
What is the equation for standard error?
SE = Standard Deviation / √n
What is the equation for 95% confidence interval?
95% CI = mean ± 1.96*SE
What is the 95% confidence interval
The range of numbers you can be 95% confident that contain the true population mean
What is a p value?
The probability of obtaining your results if the null hypothesis is true
For the p value to be significant, what two things have to be true?
- It has to be less than 0.05
2. The null value cannot be in the 95% confidence interval
What is regression?
A mathematical process to explore the association of multiple factors on an outcome
What is regression?
A mathematical process to explore the association of multiple factors on an outcome
