Psych 2220 Midterm 3

nominal variable

a variable used for observations that have categories, or names, as their values

ordinal variable

a variable whose categorical values possess some kind of order

ratio variable

A variable that meets the criteria for interval variables but also has a meaningful zero point

single sample t test

hypothesis test in which we collect data to a population for which we know the mean but not the standard deviation

single-sample t test

hypothesis test in which we compare a sample from which we collect data to a population for which we know the mean but not the standard deviation

as the sample size increases what happens to the corresponding t distribution?

it more closely approximates the z distribution

t-distributions

the t distributions help us specify how confident we can be about research findings, we want to know whether or not we can generalize what we have learned about one sample to a larger popuation

paired-samples t test

used to compare two means for a within groups design, a situation which every participant is in both samples, also called a dependent-samples t test

independent samples t-test

used to compare two means, for a between groups design, a situation in which each participant is assigned to only one condition

standard error

the standard deviation of a distribution of means

how to find scores that fall between 2 z scores

(% to mean + 50) + % in tail

how to find scores that are at least as extreme as 2 z scores

(50 - % to mean) + % in tail

six steps of hypothesis testing

1. Identify populations 2. state both hypothesis 3. critical values (p table)

paired samples t-test

1.difference between scores x2-x1 2.add up differences and divide by N 3.diff-mean differences 4.square the results 5.add sum of squared deviations that will be numerator 6.solve for standard deviation sqrt num/n-1 7.find standard error with previous result 8.mean difference - 1 / standard error

how to find scores above z score

100 - %in tail

how to find scores below zvscore

100 - %in tail

standard deviation

a computed measure of how much scores vary around the mean score

variances

changes that have occurred over time.

cohen's d

d=(M-u)/sd, measure of effect size that assesses the difference between 2 means in terms of standard devation

correlational studies

examine relationships between variables

type 2 error

failing to reject a false null hypothesis

What is an assumption of the independent-samples t test, but not an assumption of the one-sample t test?

homogeneity of variance

statistical power

measure of the likelihood that we will reject the null hypothesis, given that the null hypothesis is false

what does a z score of 0 represent

no standard deviations above or below the mean

central limit theorem

refers to how a distribution of means is a more normal distribution than a distribution of scores, even when the population distribution is not normal

type 1 error

rejecting a true null hypothesis

distribution of means

same mean as a distribution of scores from the same population , but a smaller standard deviation

point estimates

sample mean and sample proportion

Which of the following sampling distributions is used when conducting a paired-samples t test?

sampling distribution of mean differences

sample standard deviation

sqrt(x-M)squared/N

interval estimates

the extent to which point estimates are likely to be in error

degrees of freedom

the number of scores that are free to vary when we estimate a population parameter from a sample

interval variable

the order matters, and the distance between data points are all equal. ex: temperature

independent events

the outcome of one event does not affect the outcome of the second event

conditional probabilities

the probability of one event given the known outcome of a related event

experiments

the use of control and experimental groups and dependent and independent variables to test causation

95% confidence interval

upper/lower mean +/-1.96*SEM SEM = standard dev/root(n)

discrete variables

values that can be counted

continuous variables

variables that take on any value

when do we use a t distribution, instead of the z distribution, to conduct a hypothesis test comparing two means?

when we do not know the population standard deviation