Psych 240 final

(Ho) Null Hypothesis

The normal state of affairs, in which there is nothing interesting going on

(Ha) Alternative Hypothesis

A change from the normal state of affairs

Null hypothesis significance testing (NHST)

the procedure by which we decide whether to reject the null hypothesis, in favor of the alternative

P value

p<0.05 reject the null

p>0.05 fail to reject the null

p hacking

when researchers "hack" their results to lower p values to achieve statistical significance

Type 1 error

rejecting the null when the null is actuall true

Type 2 error

failing to reject the null when the null is false

power

the probability that my study will successfully reject the null if the null is actually false

effect size

used to refer to how wrong the null is. it would be the difference between true possibility of flipping heads and our null value of 0.05

The sampling distribution of the mean

a probability distribution created by taking all possible random samples of a fixed size from a population and plotting their means

Population mean: Quantity

N

Population mean: mean

Population mean: variance

Population mean: sd

Sample mean: quantity

n

Sample mean: mean

Sample mean: variance

Sample mean: sd

Standard Error of the mean (SEM)

the standard deviation of a sampling distribution

Central Limit Theorem

The theory that, as sample size increases, the distribution of sample means of size n, randomly selected, approaches a normal distribution.

1 sample t test

When the null hypothesis is about the value of a single mean

matched pairs t test

when the null hypothesis is about the mean difference between 2 measurements from each individual

2 sample t test

when the null hypothesis is about the differences between 2 population means

1 way anova

when the null hypothesis is about the differences between multiple (3 or more) population means

2 way anova

when the null hypothesis is about differences between multiple population means, with 2 grouping variables

correlation/regression

relationship between two quantitative variables

binomial test

a method used to determine if the observed proportion of successes in a sample differs significantly from an expected population probability

chi square test for goodness of fit

used when null hypothesis is about the distribution of a categorical variable

chi-square test of independence

used when the null hypothesis is about the independence of 2 categorical variables

barplot

to compare numerical values across diff categories

histogram

to visualize the distribution, shape, center, and spread of large continuous numerical datasets

boxplot

to visualize the distribution of numerical data when comparing multiple groups

plot of discrete probability distribution

to visualize and analyze the likelihood of specific, countable outcomes for a random variable

density curve

Graph of a continuous probability distribution

plot of group means with error bars

to visualize the mean value of different categories of experimental groups while showing the precision of that estimate of the variability of the data.

scatterplot

to visualize the relationship, correlation, and patterns between 2 numerical variables

t stat (1 sample)

t stat (2 sample)

chi square equation

confidence interval

Z score

standard deviation

variance

mean

correlation coefficient r

F test statistic

descriptive statistics

numerical data used to measure and describe characteristics of groups. Includes measures of central tendency and measures of variation.

inferential statistics

numerical data that allow one to generalize- to infer from sample data the probability of something being true of a population

quantitive variable

a characteristic that can be measured numerically (height, age, number of things)

categorical variable

places an individual into one of several groups or categories (color, blood type)

discrete variable

a quantitative variable that has either a finite number of possible values or a countable number of possible values (number of children in classroom)

continuous variable

a quantitative variable that has an infinite number of possible values that are not countable (age, temp.)

ordinal scale

a scale of measurement in which the measurement categories form a rank order along a continuum (survey satisfaction rating)

interval scale

A quantitative measurement scale that has no "true zero," and in which the numerals represent equal intervals (distances) between levels (e.g., temperature in degrees).

ratio scale

measurement that has a natural, or absolute, zero and therefore allows the comparison of absolute magnitudes of the numbers (10 degrees is half is warm as 20 degrees)

frequency table

A table used to show the number of times something occurs.

contingency table

Table displaying frequency distribution of variables.

right skew

mean is greater than median

left skew

mean is less than median

unimodal distribution

A distribution with one peak

bimodal

distributions with two modes

68-95-99.7 rule

in a normal model, about 68% of values fall within 1 standard deviation of the mean, about 95% fall within 2 standard deviations of the mean, and about 99.7% fall within 3 standard deviations of the mean

normal distribution

a bell-shaped curve, describing the spread of a characteristic throughout a population

central limit theorem

The theory that, as sample size increases, the distribution of sample means of size n, randomly selected, approaches a normal distribution.

Cohen's d

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

intercept of regression line

Value of dependent variable when independent variable is zero.

slope of regression line

represents the change in y (response variable) for a unit change in x (predictor variable)

Q1, Q3, and IQR

- The 25th percentile is also called the first quartile, Q1.

- The 50th percentile is also called the median.

- The 75th percentile is also called the third quartile, Q3.

- Between Q1 and Q3 is the middle 50% of the data. The range

these data span is called the interquartile range, or the IQR. IQR = Q3 - Q1

degrees of freedom

The number of individual scores that can vary without changing the sample mean. Statistically written as 'N-1' where N represents the number of subjects.

margain of error

an amount (usually small) that is allowed for in case of miscalculation or change of circumstances.

Kurtosis

Bayes' Theorem

The probability of an event occurring based upon other event probabilities.

Bayes factor

a ratio of the likelihoods of two competing hypotheses that quantifies the level of support for one hypothesis relative to the other. Used as an alternative to classical hypothesis testing

Prior Distribution

Models the many plausible values of the unknown quantity to be estimated in Bayes interference

Posterior Distribution

Probability distribution for a variable after adjustment for empirical evidence on its likely value.