psych analysis 10 - descriptive statistics

frequencies (distributions)

systematic summary or graph showing how often specific scores, categories, or ranges of values occur in a dataset

types of descriptive statistics

• central tendency - descriptive statistics that identify the single most representative or typical value in a dataset

• variability (aka spread/dispertion) - describes the degree to which scores or data points differ from one another and from the center of a distribution.

• Z score - measures how many standard deviations a raw test score or data point is above or below the population mean

descriptive statistics

summarize and describe data using measures of central tendency (mean, median, mode) and variability (range, variance, standard deviation).

central tendency

descriptive statistics that identify the single most representative or typical value in a dataset

• mean

• median

• mode - most frequent

• outliers

variability

how spread out the data is, include range, variance, and standard deviation

z score

measures how many standard deviations a raw test score or data point is above or below the population mean

• informs us of where a person’s score falls in the distribution, relative to the mean

standard deviation

a statistical measure that quantifies the average distance or spread of scores around the mean of a dataset

normal distribution

symmetrical and bell shaped

positive skew distribution

data points cluster at the lower end and a small number of extremely high scores pull a long tail toward the high end

negative skew distribution

data points cluster at the higher end and a small number of extremely low scores pull a long tail toward the low end

bimodal distribution

two distinct peaks

range (variability)

difference between highest and lowest values in a data set

variance (variability)

how far data values spread out from mean on average

• average of the squared difference from the mean