standard error, effect size, confidence intervals Flashcards
what are degrees of freedom
number of scores in a given set that are free to vary
what is standard error?
standard deviation of a number of sample means
indicates how much we can expect a sample’s mean to differ from the actual population mean
helps to understand how accurately the sample represents the whole population
what is the difference between standard error and standard deviation
standard deviation describes variability within a single sample, while standard error describes variability across multiple samples
small vs large standard error
small standard error = sample averages are usually close to population average
large standard error = sample averages more spread out and less consistent
what is a confidence interval
range of means, within which the population value (based on our data) is most likely to lie
usually calculated at the 95% confidence interval
what is effect size?
refers to magnitude of the impact of some variable on another
these indices are independent of sample size
they do not tell us whether the results could have been due to chance
what is the significance fallacy
refers to the mistaken belief that a statistically significant result automatically implies practical or meaningful importance
effect size plays a crucial role in meta analysis and power analysis. why?
meta: used to summarise magnitude of results across different studies
power: helps determine sample size needed to detect an effect
common measures of effect size
cohen’s d: comparing difference between two groups
Pearson’s r: assessing strength of linear relationship between two variables
r-squared: represents proportion of variance in one variable that is explained by the other variable. ranges from 0-1
small medium or large effect size? (Cohen, 1969)
small: real, but difficult to detect, small psychological significance
medium: large enough to be visible to naked eye
large: grossly perceptible and therefore large
