Exam 2

Question 1

interval estimate

Answer 1

based on our sample statistic, range of sample statistic we would expect if we repeatedly sampled from the same population. Confidence interval

Question 2

point estimate

Answer 2

summary statistic - one number as an estimate of the population (what we’ve been doing so far). Mean

Question 3

how to create a confidence interval for a z statistic

Answer 3

1. draw a normal curve with the sample mean at the center
2. indicate the bounds of the confidence interval on either end of the drawing
3. look up the z statistics for the lower and upper ends of the confidence interval in the z table. (always -1.96 and 1.96 for 95% confidence interval)
4. convert the z statistics to raw means for each end of the confidence interval (Mlower = -z(σM)+Msample) (Mupper = z(σM)+Msample)
5. check your answer; each end of the confidence interval should be exactly the same distance from the sample mean

Question 4

confidence interval

Answer 4

an interval estimate based on the sample statistic; it includes the population mean a certain percentage of the time if we sample from the same population repeatedly

Question 5

effect size

Answer 5

shows how much two populations don’t overlap (the further apart, the bigger the effect size)

Question 6

cohen’s d

Answer 6

measures effect size by assessing the difference between two means using standard deviation. d= (M-u)/σ

Question 7

meta-analysis

Answer 7

a study that involves the calculation of a mean effect size from the individual effect sizes of many studies (adds statistical power by considering many studies at once. Helps resolve contradictory findings)

Question 8

file drawer analysis

Answer 8

statistical calculation done following a meta-analysis of the number of studies with null results that would have to exist so that a mean effect size would no longer be statistically significant

Question 9

statistical power

Answer 9

a measure of the likelihood that we will reject the null hypothesis, given that the null hypothesis is false. Affected most directly by sample size. Between 0.00 and 1.00 (0%-100%). Minimum of 0.80 (80%) probability needed to conduct a study

Question 10

By increasing statistical power, the probability of making a _____ error is _____

Answer 10

Type II, decreased

Question 11

As the overlap between distributions being compared decreases, the effect size:

Answer 11

increases

Question 12

Power can be thought of as the percentage…

Answer 12

of the distribution of means, centered around the sample mean, that falls within the critical cutoff regions, where the null hypothesis can be rejected

Question 13

A 95 percent confidence interval of (167, 185) is calculated. What is the sample mean?

Answer 13

176

Question 14

The _____ estimate acknowledges the amount of uncertainty in the _____ estimate by reporting the margin of error

Answer 14

interval; point

Question 15

standard deviation when estimating from a sample

Answer 15

s = √Σ(X-M)^2/(N-1)

only thing that differs is - 1 in denominator

Question 16

t distribution size when samples are small

Answer 16

wider and flatter than z distribution

Question 17

t distribution size when samples are large

Answer 17

closer to z distribution shape

Question 18

standard error for t statistic

Answer 18

sM=s/√N

s means standard deviation for sample

Question 19

t statistic

Answer 19

the distance of a sample mean from a population mean in terms of the estimated standard error

Question 20

t statistic formula

Answer 20

t = (M-μM)\sM

only thing different from a z statistic formula is that you use estimated standard error in denominator

Question 21

single-sample t test

Answer 21

used to compare data from one sample to a population for which we know the mean but not the standard deviation (ex: comparing the mean of a sample against an expected value)

Question 22

degrees of freedom

Answer 22

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

Question 23

degrees of freedom formula

Answer 23

df = N - 1

Question 24

dot plot

Answer 24

a graph that displays all the data points in a sample, with the range of scores along the x-axis and a dot for each data point above the appropriate value

Question 25

steps to create a dot plot

Answer 25

1: determine the lowest score and highest score of the sample
2: draw an x-axis and label it, including the values from the lowest through highest scores
3: place a dot above the appropriate value for every score

Question 26

t distributions

Answer 26

similar to the z distribution, except we must estimate the standard deviation from the sample

Question 27

we consider ____ instead of N when we assess estimated test statistics against distributions

Answer 27

degrees of freedom

Question 28

to conduct a single-sample t test, we follow the same six steps of hypothesis testing as the z test, except we estimate the ____ before we calculate standard error

Answer 28

standard deviation from the sample

Question 29

small effect size for Cohen’s d

Answer 29

0.2

Question 30

medium effect size for Cohen’s d

Answer 30

0.5

Question 31

large effect size for Cohen’s d

Answer 31

0.8

Question 32

paired-samples t test (dependent-samples t test)

Answer 32

compares two mean for a within-groups (every participant is in both samples). Used to analyze the data from many studies. Participants have two scores (one score in each condition) (ex: before and afters)

Question 33

distribution of mean differences

Answer 33

used for paired-samples t test

Question 34

order effects

Answer 34

how a participant’s behavior changes when the dependent variable is presented for a second time (also called practice effects). When responses are influenced by the practice of having already completed the tasks once

Question 35

counterbalancing

Answer 35

minimizes order effects by varying the order of presentation of different levels of the independent variable from one participant to the next

Question 36

what’s in the center of a paired-samples t test curve?

Answer 36

sample mean difference

Question 37

In which statistical test do we calculate a difference score for each individual, take the mean of the difference scores, and perform a single-sample t test on them to compare two sample means?

Answer 37

paired-samples t test

Question 38

For the paired-samples t test, the comparison distribution:

Answer 38

contains means of difference scores

Question 39

r^2

Answer 39

another measure of effect size (t^2obs / t^2obs + df)

Question 40

small effect size for r^2

Answer 40

0.01

Question 41

medium effect size for r^2

Answer 41

0.09

Question 42

large effect size for r^2

Answer 42

0.25

Question 43

independent-samples t test

Answer 43

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

Question 44

formula for calculating degrees of freedom in an independent-samples t test

Answer 44

dftotal = dfx + dfy

Question 45

pooled variance

Answer 45

weighted average of the two estimates of variance- one from each sample- that are calculated when conducting an independent-samples t test

Question 46

To determine the critical values for an independent-samples t test, we need to know the:

Answer 46

total degrees of freedom

Question 47

independent-samples t test uses

Answer 47

a distribution of differences between means