Statistics Review- research methods in psychology

descriptive statistics

A set of statistics used to organize and summarize the properties of a set of data.

data matrix

A grid presenting collected data.

frequency distribution

A table showing how many of the cases in a batch of data scored each possible value, or range of values, on the variable.A table showing how many of the cases in a batch of data scored each possible value, or range of values, on the variable.

frequency histogram

A data visualization technique showing how many of the cases in a batch of data scored each possible value, or range of values, on the variable.

dot plot

A data visualization technique in which every data point for a given variable is represented.

central tendency

A value that the individual scores in a dataset tend to center on. See also mean, median, mode.

mode

A measure of central tendency that is the most common score in a set of data.

bimodal

Having two modes, or most common scores.

multimodal

Having two or more modes, or most common scores.

median

A measure of central tendency that is the value at the middlemost score of a distribution of scores, dividing the frequency distribution into halves.

mean

An arithmethic average; a measure of central tendency computed from the sum of all the scores in a set of data, divided by the total number of scores.

variance

A computation that quantifies how spread out the scores of a sample are around their mean; it is the square of the standard deviation.

standard deviation

A computation that captures how far, on average, each score in a dataset is from the mean.

box plot

A data visualization technique that depicts a sample's median, interquartile range (25th and 75th percentiles), and outliers.

outlier

A score that stands out as either much higher or much lower than most of the other scores in a sample.

z score

A computation that describes how far an individual score is above or below the mean, in standard deviation units.

Cohen's d

A measure of effect size indicating how far apart two group means are in standard deviation units.

inferential statistics

A set of techniques that uses the laws of chance and probability to help researchers make decisions about what their data mean and what inferences they can make from the data.

estimation

An approach to inferential statistics that uses data from a sample to calculate an effect size and a 95% confidence interval, with the goal to predict the magnitude of some value in the population.

null hypothesis significance testing (NHST)

An inferential statistical technique in which a result is compared to a hypothetical population in which there is no relationship or no difference.

point estimate

A single estimate of some population value (such as a percentage, a correlation, or a difference) based on data from a sample.

confidence interval (CI)

A given range indicated by a lower and upper value that is designed to capture the population value for some point estimate (e.g., percentage, difference, or correlation); a high proportion of CIs will capture the true population value.

standard error

The typical, or average, error researchers make when estimating a population value.

dependent samples design

A design in which each person has two scores because they were tested under two conditions, and we are interested in the difference between them. Also called a paired design.

p value

In NHST, the probability of getting the result in a sample or one more extreme, by chance, if there is no relationship or difference in the population.

statistically significant

In NHST, the conclusion assigned when when p < .05; that is, when it is unlikely the result came from the null hypothesis population.

alpha level

The value, determined in advance, at which researchers decide whether the p value obtained from a sample statistic is low enough to reject the null hypothesis or too high and thus retain the null hypothesis.

not statistically significant (n.s.)

In NHST, the conclusion assigned when p > .05; that is, when it is likely the result came from the null hypothesis population.