week 8 Flashcards

1
Q

which test assesses change over two time points on a single dichotomous variable

A

McNemar test - change between two time points ex. students thoughts on if a class should be required before and after taking the class

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2
Q

cells B and C in a mcnemar test represent

A

change

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3
Q

Mcnemar test only works for

A

dichotomous variables

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4
Q

critical values of chi are always looked up with an

A

unsplit alpha

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5
Q

chi square is an

A

omnibus test - shows that cells differ but not which ones

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6
Q

how do you calculate DF for a mcnemar test

A

DF=1

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7
Q

How are standardized residuals calculated in a bivariate chi-square analysis?

A

By dividing the difference between observed and expected frequencies by the square root of the expected frequency.

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8
Q

When will the phi coefficient and Cramer’s v be identical?

A

When at least one of the variables has only two categories.

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9
Q

When calculating Cramer’s v, what does k represent?

A

The number of rows or columns in the cross tabulation, whichever is less

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10
Q

phi coefficient always ranges from

A

0-1

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11
Q

t/f you can not have a negative phi coefficient

A

true because it is directly estimated from chi-square which is always positive

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12
Q

as the size of cross-tabulation increases so does

A

value of chi-square

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13
Q

how do you calculate the phi coefficient?

A

square root of obtained value of chi-square divided by overall N size

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14
Q

how to calculate expected value

A

product of the marginal totals for the row and column in which the cell is located

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15
Q

the simplest way to conceptualize a difference between two time points

A

mean difference

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16
Q

what is the main difference between univariate and bivariate chi-square analysis

A

expected value calculations

17
Q

what is the bivariate chi-square

A

association between two categorical variables

18
Q

two bivariate applications of chi square

A
  1. Change over time within a single variable
    - McNemar test
  2. Association between categorical variables
    - phi coefficient, cramer’s v
19
Q

what kind of statistic is the mcnemar test

A

chi square statistic

20
Q

what kind of analysis is the mcnemar test

A

A repeated measures analysis
- must survey the same group of individuals twice
- intended to evaluate change over time

21
Q

what is null hypothesis for mcnemar test

22
Q

in a 2x2 chi square analysis what will the DF be

23
Q

the mcnemar test only works for

A

dichotomous variables and designs with only two time periods

24
Q

cramers v and phi coefficient test what kind of data

25
in a cross table what are we comparing
model fit for our observed data
26
what can standardized residuals be treated as
may be treated like z-scores, with scores greater than +2 or less then -2 considered to be significant
27
when can we consider a cell to be significantly different from our expectation
If the standardized residual is greater than +2 or less then -2
28
t/f: chi square helps determine the magnitude of association
FALSE- it identifies if there is an association but not the magnitude
29
phi coefficient ranges from
0-1, cant have negative phi coefficient bc it is a direct estimate from chi square and chi square cant be negative
30
What can larger cross tabulation tables result in?
Phi coefficients > 1 - as the size of our cross tabulation (ie as the number of cells increases) the value of chi square tends to get larger. this is why the df for chi-square analysis is based on the number of rows and columns in our cross table - this systematic increase in the size of the chi-square makes it increasingly likely that the chi coefficient will blow past our conceptual upper limit of 1 - thus we need to apply a correction factor to our phi coefficient so that the correlation still ranges from 0-1
31
cross tables larger than 2x2 require a
correction
32
what is the simplist corrected cross-tabular association
cramers v
33
rule for chi square
80% of expected values have to be greater than 5, all expected values must be larger than one
34
the magnitude of association is identified using
a phi coefficient or cramers v