normal distributions

why is it useful to look at distributions?

helps visualize the spread (or variability) in the data

what are the characteristics of a normal distribution?

unimodal, “bell shaped”, perfectly symmetrical, mean, median, mode all equal, and percent of scores below the curve is always the same

what does it mean if you have a skewed distribution?

a distribution in which one of the tails is pulled away from the center

what is a positive skew?

tail points to the right

what is the negative skew?

tail points to the left

what are floor and ceiling effects?

positive skew = floor effect

negative skew = ceiling effect

what is kurtosis?

“curvedness” or “peakedness” of a distribution

what is leptokurtic?

thin distribution

what is platykurtic?

flat distribution

does transforming scores change the relationship between the variables in your data?

does not change the relationship between variables

what is a z-score?

the number of standard deviations a particular score is from the mean

why are z-scores useful?

thinking about normal distribution, directly comparing scores on different scales, and determining percentiles