Stata

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Stata

• A statistical package for epidemiologists

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Packages compared
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Packages compared
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Packages compared
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Packages compared
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Why Stata

• Pro
• Aimed at epidemiology
• Many methods, growing
• Graphics
• Structured, Programable
• Comming soon to a course near you
• Con
• Memorygtfile size

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Syntax

• Full syntax
• by varlist command varlist if in ,
  options
• Examples
• mean age
• mean age if sex1
• by sex, sort summarize age
• summarize age ,detail

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Ways of working

• Testing
• p-values
• Estimation
• Estimate with confidence interval

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Bivariate
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Mean with CI

• Advanced features
• Standarization
• Clustering
• Bootstrap

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Median and percentiles with CI
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Compare means
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Compare means, T-test

• ttest weight, by(sex) unequal uneq. var.
• ttest var1var2 paired test

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Graphics
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Plottypes
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Legend with extra information
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Density with min, max and fractiles
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Scatter with fitline extra point
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Bar with labels inside
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Regression results
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Regression
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Purpose of regression

• Prediction
• Use an estimated model to predict the outcome
  given covariates in a new dataset
• Estimation
• Estimate association between outcome and
  covariates adjusted for the other covariates

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Linear regression

• Model
• Model fitting
• Cofactors in/out
• Interactions
• Test of assumptions
• Independent errors
• Linear effects
• Constant error variance
• Influence, robustness

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Linear regression, exposure only
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Add confounders and compare
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Assumtions and influence

• Test of assumptions
• Independent errors
• Linear effects
• Constant error variance
• Influence, robustness

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Influence
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Binary regression

• Odds ratio, OR
• binreg y x1 x2, or Link logit
• Risk ratio, RR
• binreg y x1 x2, rr Link log (ln)
• Risk difference, RD
• binreg y x1 x2, rd Link identity

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Odds ratio, Relative risk, Risk Diff
Problems convergence
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Help
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Search for help

• General
• help command
• findit keyword search the net
• Examples
• help table
• findit GAM
• My home page
• http//folk.uio.no/heins/

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Books

• A visual guide to Stata graphics
  by M.N. Mitchell
• Data Analysis Using Stata by Ulrich Kohler and
  Frauke Kreuter
• Statistics with Stata (Updated for Version 9) by
  Lawrence C. Hamilton
• Multilevel and longitudinal modeling using Stata
  by S. Rabe-Hesketh, A. Skrondal