Multivariate Statistical Analysis and Modeling

Question 1

what are statistics used for?

Answer 1

to discern justifiable differences in quantitative patterns

Question 2

give 3 classic statistical tests and why they are not practical for epidemiology

Answer 2

1. basic t tests
2. ANOVA
3. Chi squared
   too burdensome to apply to situations where multiple variables and their interactions are in question

Question 3

describe the T test and give an example of how it could be used

Answer 3

tests whether significant differences, not attributable to random chance, are present in continuous data; could use for averaging hemoglobin levels in two different groups of people

Question 4

what does the chi squared test do? give an example

Answer 4

tests significance between groups of non-continuous data
examples are infected versus not infected, vaccinated or not vaccinated

Question 5

what are chi squared tests useful for?

Answer 5

2x2 contigency tables

Question 6

what is Fisher’s exact test?

Answer 6

tests for significance in much the same way as the chi squared test does, but works with ANY SIZE DATA SET!!

Question 7

what does the Fisher’s exact test give?

Answer 7

gives an exact P value rather than an approximation like other tests do

Question 8

what can Fisher’s exact test also be applied to?

Answer 8

2x contigency tables

Question 9

what is mutlivariable regression? (2)

Answer 9

1. multiple independent variables are regressed on a single dependent variable
2. all variables are considered together to discern correlations either individually or in combinations

Question 10

what does multivariate analysis allow for?

Answer 10

allows more than two variables to be analyzed at once

Question 11

is multivariable regression a type of multivariable analysis?

Answer 11

not usually considered under the heading, but is technically multivariate analysis

Question 12

what are the 2 general types of multivariate analysis technique?

Answer 12

1. asnalysis of dependence
2. analysis of independence

Question 13

describe the analysis of dependence multivariate analysis technique

Answer 13

where one or more variables are dependent variables, to be explained to predicted by others

Question 14

give 3 analysis of dependence multivariate analysis tests

Answer 14

1. multivariable regression
2. PLS (partial least squares)
3. MDA (multiple discriminant analysis)

Question 15

where is multivariable regression analysis often seen?

Answer 15

in cohort studies

Question 16

describe the analysis of independence multivariate analysis method

Answer 16

no variables are thought of as dependent, just look at the relationship among variables, objects, or causes

Question 17

give 2 analysis of independence multivariate analysis tests

Answer 17

1. cluster analysis
2. factor analysis

Question 18

in most cases, why is data anlaysis done?

Answer 18

to test the association between two or more variables (bivariate)

Question 19

what is often the aim of analysis in health research?

Answer 19

1. to establish the association between risk factor and disease
2. to establish the association between therapy and outcome (patient oriented research)

Question 20

what are the 2 types of regression models?

Answer 20

1. simple linear (y = mx+b)
2. multiple linear regression (y = b + m1x1 + m2x2…)

Question 21

what is a model?

Answer 21

a set of theoretically and/or evidence based associations between variables

Question 22

what does data analysis test?

Answer 22

data analysis tests the extent to which the proposed theoretical associations are observed in the data

Question 23

what is model development based on?

Answer 23

model development is based on previous knowledge (previous research evidence about associations)

Question 24

what is model development mostly about?

Answer 24

model development is mostly about deciding which independent variables (risk factors) should be in the multivariate analysis

Question 25

what do SIR models mean/stand for?

Answer 25

S: susceptible, S(t): the disease-susceptible people in a population
I: infectious, I(t): those capable of transmitting an infection to others
R: recovered R(t): those that have been infected and recovered

Question 26

what do vaccines do in terms of the SIR model?

Answer 26

try to move people from susceptible to recovered (since vaccine is like a mini infection)

Question 27

what are the 3 assumptions of the Kernack-McKendrick model?

Answer 27

1. assumes a well-defined, closed, and fixed population
2. assumes an infected person is instantaneously infective and infectivity lasts duration of disease state
3. assumes a homogenous population with no genetic variation or demographic differences