STATS Flashcards
what is the average deviation?
calculates the average deviation from the mean across all scores
how do you calculate the average deviation?
- calc mean
- calc deviation of each score
- calc mean deviation
how do you calculate the standard deviation?
- calc mean
- calc deviation of each score
- square your deviations
- calc variance - calc mean using total N-1
- square root answer
what is a sampling error?
error associated with examining stats from a sample rather than a population
what is a sampling distribution?
the spread of a sample statistic obtained by representative samples from a population - tells us how a statistic changes between samples
what is the sampling distribution of the mean also known as?
standard error
what does the standard error tell us about the means of a sample from a population?
tells us if a sample is representative of its population
what are the characteristics of a normal distribution curve?
- bell shaped
- area = 1
- symmetrical, centered on pop mean
what are z scores?
the position of a raw score in terms of its distance from the mean when measured in standard deviation units from the mean
how would you answer this question: ‘what is the probability of picking someone with an IQ of more than 112 from a normally distributed population (100,15)?
- calc z score = x - (pop mean/pop sd)
- use p table to find probability value
as this is a more question, you must use the below column, unless it has a negative sign which means you must use the opposite column
how would you answer this question: ‘what is the probability of picking someone with an IQ between 70 and 115 from a normally distributed population (100,15)?
- calculate z scores for both values = x - (pop mean/pop sd)
- find p scores of both
- subtract them from each other to get the area
would we expect a larger or smaller standard error with a bigger sample?
smaller standard error, more representative of parent population
how do you calculate the standard error?
s.d of parent pop/ rootN
what does a 95% confidence interval tell you?
if we repeated our sampling over, calculated a new confidence interval each time using a new sample mean, the population mean would land in the intervals 95% of the time
how do you calculate a 95% confidence interval?
UPPER = pop mean -(1.96 x standard dev)
LOWER = pop mean + (1.96 x standard dev)
when you don’t have the population mean or standard dev?
use sample mean or standard dev to get an indication of what the population parameters would look like
what is null hypothesis significance testing?
works out if a sample mean is different from the theoretical population mean
what is a type 1 error?
incorrect rejection of a true null - even if p is small, data was unusually extreme