Univariate ANOVAs and Nonparametrics Flashcards
what are the different ANOVAs, univariable?
one way ANOVA
repeated measures ANOVA (single factor)
what are the different nonparametric tests of ANOVAs?
Kruskal-Wallis test
Friedman test
how do we compare data from more than 2 groups?
ANOVA
if we have three groups: people with Associates, Bachlors and no degree, what would our ANOVA test hypothesis be if we expect different mean scores among the groups?
mu1=mean of group 1 (Associates
mu2=mean of group 2 (Bachelors)
mu3=mean of group 3 (no degree)
H0: mu1=mu2=mu3
Ha: some mui are different
should we conduct multiple independent samples t tests for every pairing of groups if we have a sample with more than 2 groups?
no!
what are the problems with using multiple independent t tests for a sample with more than 2 groups?
this won’t directly evaluate the H0 vs Ha, just bits and pieces of it
this becomes more complex with larger #s of groups (or with 10 groups, there are 45 pairings)
compounding type 1 error (BIGGEST PROBLEM)
what is the biggest problem with running multiple independent t tests with a sample of more than 2 groups?
compounding type 1 error
what is an example of compounding type 1 error?
when you have 3 tests with 5% of type 1 error, this becomes a 14% chance of type 1 error in any of the three
what is family wise error rate (FWER)?
the probability of at least one type 1 error on a group of tests (the compounding type 1 error)
t/f: FWER becomes worse with more pairings
true
when we do multiple independent t tests for multiple groups, we want to test if Mu1=mu2=mu3…, but what we end up testing is:
mu1=mu2
mu1=mu3
mu2=mu3
t/f: in order to test H0 of more than 2 groups, pair off groups and conduct several independent samples t tests
false!!! do not do this!!!
what is the method for controlling FWER?
ANOVA
what is analysis of variance (ANOVA)?
the general procedure for making statistical comparisons of many types based on “breaking down” simple variance calculations
what is the numerator of the equation for sample variance?
sum of (xi-x bar) squared
the numerator of the equation for sample variance is equal to what?
sums of squares
calculating the sum of squares around a single, overall mean makes sense for one group, what is a better measure of overall dispersion for groups w/potentially dif means?
doing two “pieces” in sum of squares based around the group means and global/grand mean
what are the 2 pieces in sum of squares for multiple groups?
systematic variation
random variation
what is systematic variation?
differences among groups (deviations from the grand/global mean to group mean)
what is random variation?
natural randomness (deviation of data from the group means)
t/f: there are 2 sources of deviation from the overall mean
true
what are the 2 sources of deviation from the overall mean?
systematic deviation
random deviation
what is systematic deviation?
group averages to the overall average
what is random deviation?
observations (data points) to group averages
what are the 2 pieces of the sum of squares doing?
comparing the means among groups by comparing systematic and random deviations
is systematic deviation variation bw or w/in groups?
bw groups
is random deviation variation bw or w/in groups?
w/in groups
if systematic deviation is big…
group means may be dif
if random deviation is big…
lots of random error may be occuring w/in groups
if F statistic is large, the p is ___ and we ___ the null
small, reject
what are the formal names for the 3 deviations?
total sum of squares
bw groups sum of squares
w/in groups sum of squares
what is the total sum of squares (SST)?
deviations from observations to overall mean
sum of (observation-overall mean)^2
what is the bw groups sum of squares (SSB)?
deviations from group means to overall mean
sum of (group mean-overall mean)^2
when the groups means are different, is the SSB large or small?
large
what is the w/in groups sum of squares (SSW)?
deviations from observations to group means
sum of (observation-group mean)^2
when data are highly variable w/in a group, is the SSW large or small?
large
what is the equation for SST
SST=SSB+SSW
SST is the sum of what two things?
SSB and SSW
if the SSB is a larger contribute to SST than SSW, there is evidence of…
different groups means (Ha supported)
if SSB is the larger contributer to SST, if Ha or H0 supported?
Ha
if SSW is a larger contributer to SST than SSB, there is evidence of…
equal group means (H0 supported)
if SSW is the larger contributer to SST, is Ha or H0 supported?
H0
does SSB have a high inter-error deviation or intra-error deviation?
inter-error deviation
does SSW have a high inter-error deviation or intra-error deviation?
intra-error deviation
when data is clustered very close to the group means, is the SSB/SSW small or large?
SSW is small
if data is very dispersed around group means, is the SSB/SSW small or large?
SSW is large
if group means are dispersed from the grand mean, is the SSB/SSW small or large?
SSB is large
if group means are close to the grand mean, is the SSB/SSW small or large?
SSB is small
to conduct a hypothesis test for a one-way ANOVA, we need what two things?
a statistic based on SSB and SSW
a reference distribution for the statistic
t/f: we need the mean of squares BW groups and W/IN groups for one-way ANOVA
true
what is the MSB (mean of squares bw groups)?
MSB=SSW/(k-1)
what is k in ANOVA testing?
the # of groups (in the GRE example, k=3 for the Associates, Bachleors, and no degree groups)
what is the MSW (mean of squares w/in group)?
MSW=SSW/(overall sample size(n)-k)
t/f: ANOVA is an expansion of independent samples t test
true
what are two other names for the one way ANOVA test?
Fisher’s ANOVA
univariate ANOVA
what is the goal of the one-way ANOVA test?
to examine whether mean values from several (>2) populations are equal
what is the test statistic for one way ANOVA?
F
what is the F equation?
F=MSB/MSW
is the F distribution symmetrical?
nope
how many DF are required for the F-distribution?
2
what are the 2 DF used in the F-distribution?
MSB: k-1 DF
MSW: n-k DF
if the DF get really large, can it approach the z distribution standard normal curve appearance?
yes
what is an outcome in the one-way ANOVA?
the variable being analyzed (Y)
the dependent variable (DV)
what is a factor in a one-way ANOVA?
a characteristic that distinguishes groups
what are some examples of factors?
biological sex, treatment types, insurance status
what are levels in one-way ANOVA?
the groups defined by a factor
what are examples of levels?
male, female, and intersex in the factor of biological sex
intensive overground gait training, treadmill training, and exoskeleton training in the factor of treatment type
what are the assumptions for ANOVA?
continuous data
independence of data
normality
homogeneity of variance
how do we test for normality in ANOVA?
the SW test if n<30
how do we test homogeneity of variance in ANOVA?
Levene/s test
t/f: normality has a large effect on ANOVA
false, it has a small effect on ANOVA
t/f: homogeneity of variance has a greater impact on ANOVA results
true