Probability and Distributions Flashcards
Define normal distribution
When data is symmetrical around central scores and the mean, median and mode are equal
What is a Gaussian Curve?
Normal distribution
What does a positive skew look like?
The peak is on the left hand side
What does a negative skew look like?
The peak is on the right hand side
How would you calculate Pearson’s coefficient of skew?
skew = 3(mean - median) / standard deviation
If the skew is <0, what is the data?
Data is negatively skewed
If the skew is >0, what is the data?
The data is positively skewed
How can you test for distribution?
Normality tests
From the mean and standard deviation of the data alone, what can we predict?
We can predict the value of y for any value of x
What test would you use for one-sample, independent and paired?
T-test
What test assumes values e.g. the mean and SD accurately reflect the population distribution?
Parametric tests
What can transforming data into Z scores help?
Helps standardise data and reduce the impact of skewness
What equation would you use when transforming data into Z scores?
Z = individual point - group mean / standard deviation
What does a Z score tell us?
Tells us how many standard deviations someone was from the mean
What are some pros of Z scores?
Can transform data to a standardised table and can compare things relative to their own population
What can we estimate about a population based on a sample?
Values and statistics
Define sampling error
The value is likely to differ from the true mean of the global population (or other samples)
What can we use to say how confident we are that our sample values represent the population?
Use the Standard Error of the mean
What is the equation for Standard Error?
SEM = Standard deviation / square root of number of datapoint
What does the Standard error tell us?
How likely it is our sample will vary from one sampling to another
What are the Standard error’s biggest influences?
Variability of the original data
What would someone use instead of the Standard error?
Confidence intervals
Define confidence intervals
The range of values that, in a certain proportion of samples, contains the true value of a statistic
What is the visual for confidence interval on a graph?
Error bars
