Master’s Essay in
Epidemiology I
P9419
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Methods |
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Luisa N. Borrell, DDS, PhD |
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October 25, 2004 |
Slide 2
Methods
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The Methods section of a proposal will provide readers with an
overview of whom you are studying and the statistical methods you will use to
answer the question or test the hypothesis posed in the problem to be addressed |
Proposal Abstract Methods
Section
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In one paragraph, present the information that best describes your
study in terms of: |
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Study design |
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Population |
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Variables to be examined |
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Outcome (s) |
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Exposures (or Interventions) |
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Covariates |
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Statistical analysis |
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Study designs and reasons
for choosing a particular design
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Observational |
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Cross-sectional |
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Case-control |
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Cohort (retrospective or prospective) |
Study Designs and
Choices
Cont…
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Experimental |
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Clinical trial |
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Community intervention trial |
Whom do you plan to study?
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Population |
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From what population were subjects recruited or selected—target (AKA
source or reference) or accessible population? |
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Were the subjects obtained consecutively, by random sampling, or as
volunteers? |
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When were the participants enrolled in the study? |
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Whom do you plan to study?
Cont…
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Population |
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What
were the characteristics in terms of age, gender, ethnicity, health status,
socioeconomic status? |
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What inclusion/exclusion criteria were used? |
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Were issues of external/internal validity
considered? |
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What are you measuring?
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Outcomes |
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Exposure |
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Covariates (Confounders, effect modifiers,
or mediator variables) |
As a review…
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Measurement can be: |
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Continuous |
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Discrete |
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Categorical |
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Two values-dichotomous |
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More than two values |
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Nominal-Unordered |
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Ordinal-Ordered |
Outcome
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How was the information to define the
outcome collected? |
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How was the outcome measured? |
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How will you define the outcome? |
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Will you have to do any recoding? |
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If defined as categorical, how many levels does the outcome variable
have? |
Exposure(s)
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How was the information to define the
exposure(s) collected? |
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How were the exposure(s) measured? |
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How will you define the exposure(s)? |
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How many levels do your categorical
exposure variables have? |
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Will you recode? |
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Collapse categories |
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Set cutpoints for continuous variables |
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Develop an index or scoring system for
combined exposures |
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Covariates
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Why might the covariate be a |
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Confounder? |
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Effect modifier? |
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Mediator? |
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How is the covariate defined? |
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Is the covariate associated with the
exposure? |
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Can the covariate cause the outcome? |
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Does the exposure/outcome relationship
vary with levels of the covariate? |
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Can the exposure cause the covariate? |
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Statistical Analysis
Slide 15
Statistical Analysis
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Descriptive |
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Continuous |
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Categorical |
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Bivariate analyses |
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Multivariable approaches |
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Any additional information |
Statistical Analysis
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Descriptive |
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Continuous |
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Bivariate analyses |
Nature of your
Outcome:
Continuous
Statistical Analysis
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Descriptive |
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Categorical |
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Bivariate analysis |
Nature of your
Outcome:
Categorical
Statistical Analysis
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Descriptive |
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Continuous |
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Categorical |
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Bivariate analysis |
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Multivariable approaches |
Bringing it all together:
Outcome and Exposure
Statistical Analysis
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Descriptive |
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Continuous |
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Categorical |
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Bivariate analysis |
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Multivariable approaches |
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Any additional information |
Any additional information
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Test for interaction |
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Test for trend |
Example
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To examine the association between head
trauma and seizures and epilepsy before and after controlling for age,
gender, family history, physical and mental health, alcohol, drug |
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Hypothesis: |
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Head trauma increase the probability of head trauma and seizures and
epilepsy after controlling for all covariates |
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This association will depend on age, with younger people having a
stronger association |
Example…
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Individuals seeking medical care in Iceland
over a 4 years period |
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Cross-sectional |
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Cohort |
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Case-control |
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Matched |
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Unmatched |
Back to our Example
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To examine the association between head
trauma and seizures and epilepsy before and after controlling for age,
gender, family history, physical and mental health, alcohol, drug |
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Hypothesis: |
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Head trauma increase the probability of head
trauma and seizures and epilepsy after controlling for all covariates |
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This association will depend on age, with
younger people having a stronger association |
Example…
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Outcome: Febrile seizures, other provoked
seizures and epilepsy |
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Binary (yes/no) |
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Exposure: Head trauma |
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Binary |
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Number of trauma |
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Example…
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Covariates: |
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Age-Continuous
and categorical |
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Gender-Categorical |
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Family
history-Categorical |
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Physical
and mental health-Summary score |
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Alcohol-Categorical |
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Drug-Categorical |
Statistical Analysis
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Descriptive |
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Continuous- t-tests, ANOVA |
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Categorical- Chi-square tests |
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Bivariate analysis |
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Continuous-continuous/categorical- r |
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Categorical-categorical-OR, RR |
Statistical Analysis
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Multivariable approaches |
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Continuous-continuous/categorical: Linear
regression |
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Categorical-categorical/continuous: Logistic
regression/Cox Proportional Regression |
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Any additional information |
Statistical Analysis
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Any additional information |
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Interaction |
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Then…
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The population for this study represents a random sample of
individuals 16 to 28 years of age seeking medical care in 4 clinics during
1992 and 1996 in Iceland. The outcome
for this study will be defined as the first diagnosed seizure, febrile or due
to other causes, after a head trauma.
Individuals seeking care for a head trauma will be considered as
exposed and those seeking care for other traumas not involving the head as unexposed. Age, gender, family history, self-rated
physical and mental health, alcohol and drug consumption will be included as
covariates. |
Then…
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Descriptive statistics will be presented for all covariates by the
outcome and the exposure status. t-, ANOVA
and chi-square tests will be used to assess significant differences
between groups. In addition, Pearson
and Spearman correlation coefficients will be used to determine the
association between the outcome and all other covariates included in the
analyses. Logistic regression will be
used to assess the strength of the association between seizures and head
trauma before and after controlling for all covariates in the analysis. An interaction term between head trauma and
age will be tested to determine whether the association between head trauma
and seizures varies with age. |