Psych 101: R Exam Terms

mean

value of a distribution that is closest to all the other scores; serves as our “best guess” about the value of any random individual score in this distribution

median

value that is in the very middle of a distribution of scores; 50% of scores in the distribution are higher than the median value, and 50% of the scores are lower than the median value

standard deviation

describes how much the average individual score differs from the mean; measure of error

standard error

estimate of how much the average individual samples might differ from the estimated slope (the slope you found in your study); measure of error

p-value

measure of significance; describes the probability that you would observe a t-value as large (or larger) than the one that you observed if the null hypothesis were true; p value greater than or equal to 0.05, our results are likely NOT due to random chance, we can disprove null hypothesis

95% confidence interval

used to find typical or expected values in data; 95% of data values (scores) should fall 1.96 standard errors above AND below the slope of the particular data set

R² value

the percent of variation in y that can be explained by x (0.07% of the belief that aliens are real can be explained by extraversion, for example)

intercept (what it measures)

what the y variable equals when all independent variables (x values) are 0

slope (what it measures)

how much y changes per every 1 unit change in x

t-value

how large the slope from your study is compared to the “average” slope you might find due to random sampling error (se = the standard error)

p-value: application to an exam question

if the null were true, we’d expect to find a slope as large or larger than the one we found less than 1% of the time