Biological Statistics Flashcards
When is the chi squared test used?
Used when looking for associations between categorical data
When is the spearman rank test?
Used when looking for associations between two continuous variables
How do you calculate standard error?
SE= Standard deviation / Square root of sample size
How do you calculate 95% confidence limits?
2 x Standard Error
What is the null hypothesis?
The hypothesis which expects no difference and all differences are due to chance
What is the significance of the P value?
P is > 0.05 means results are due to chance and not significant.
P is < 0.05 means results are not due to chance and are significant
What is the standard deviation?
The spread of data around the mean
Why do we use standard deviation?
1) Shows the reliability of the mean in repeat experiments
2) Larger SD means less reliable mean
3) Also used for standard error and confidence limits
What is the significance of overlapping confidence limits?
The probability that the difference between the means is due to chance is more than 5%.
Therefore results are not significance so we accept the null hypothesis.
What is the significance of none overlapping confidence limits?
The probability that the difference between the means is due to chance is less than 5%.
Therefore results are significance so we reject the null hypothesis.
What is the chi squared test?
The test used to show whether the difference between observed and expected value is significant or due to chance.
What do you do with the chi squared result?
Compare to standard critical value.
CSV(c^2)>CV(critical value)
If the chi squared value is greater than the critical value, the probability that the difference is not due to chance as p is less than 0.05, therefore the results are significant so we reject the null hypothesis.
CSV
What does SRCC (spearman rank) measure?
The nature and the size of correlation between 2 variables
What are the steps to calculate the SRCC?
1) Rank the data (if more than one number then add together and then divided by total number of numbers the same)
2) Find differences between the ranks for each value
3) Square them to remove any negative values
4) Calculate the sum of d^2
5) Input into formula 1-(6xsumd^2)/ n(n^2-1)
