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338 lines
13 KiB
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<meta name="author" content="Fredrik Danielsson, http://lostkeys.se">
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<title>Brandon Rozek</title>
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<main class="main-content">
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<article class="article">
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<h1>Reproducible Research Week 1</h1>
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<h2>Replication</h2>
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<p>The ultimate standard for strengthening scientific evidence is replication of finding and conducting studies with independent</p>
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<ul>
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<li>Investigators</li>
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<li>Data</li>
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<li>Analytical Methods</li>
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<li>Laboratories</li>
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<li>Instruments</li>
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</ul>
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<p>Replication is particularly important in studies that can impact broad policy or regulatory decisions</p>
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<h3>What's wrong with replication?</h3>
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<p>Some studies cannot be replicated</p>
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<ul>
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<li>No time, opportunistic</li>
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<li>No money</li>
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<li>Unique</li>
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</ul>
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<p><em>Reproducible Research:</em> Make analytic data and code available so that others may reproduce findings</p>
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<p>Reproducibility bridges the gap between replication which is awesome and doing nothing.</p>
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<h2>Why do we need reproducible research?</h2>
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<p>New technologies increasing data collection throughput; data are more complex and extremely high dimensional</p>
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<p>Existing databases can be merged into new "megadatabases"</p>
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<p>Computing power is greatly increased, allowing more sophisticated analyses</p>
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<p>For every field "X" there is a field "Computational X"</p>
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<h2>Research Pipeline</h2>
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<p>Measured Data -> Analytic Data -> Computational Results -> Figures/Tables/Numeric Summaries -> Articles -> Text</p>
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<p>Data/Metadata used to develop test should be made publically available</p>
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<p>The computer code and fully specified computational procedures used for development of the candidate omics-based test should be made sustainably available</p>
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<p>"Ideally, the computer code that is released will encompass all of the steps of computational analysis, including all data preprocessing steps. All aspects of the analysis needs to be transparently reported" -- IOM Report</p>
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<h3>What do we need for reproducible research?</h3>
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<ul>
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<li>Analytic data are available</li>
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<li>Analytic code are available</li>
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<li>Documentation of code and data</li>
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<li>Standard means of distribution</li>
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</ul>
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<h3>Who is the audience for reproducible research?</h3>
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<p>Authors:</p>
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<ul>
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<li>Want to make their research reproducible</li>
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<li>Want tools for reproducible research to make their lives easier (or at least not much harder)</li>
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</ul>
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<p>Readers:</p>
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<ul>
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<li>Want to reproduce (and perhaps expand upon) interesting findings</li>
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<li>Want tools for reproducible research to make their lives easier.</li>
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</ul>
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<h3>Challenges for reproducible research</h3>
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<ul>
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<li>Authors must undertake considerable effort to put data/results on the web (may not have resources like a web server)</li>
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<li>Readers must download data/results individually and piece together which data go with which code sections, etc.</li>
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<li>Readers may not have the same resources as authors</li>
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<li>Few tools to help authors/readers</li>
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</ul>
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<h3>What happens in reality</h3>
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<p>Authors:</p>
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<ul>
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<li>Just put stuff on the web</li>
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<li>(Infamous for disorganization) Journal supplementary materials</li>
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<li>There are some central databases for various fields (e.g biology, ICPSR)</li>
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</ul>
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<p>Readers:</p>
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<ul>
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<li>Just download the data and (try to) figure it out</li>
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<li>Piece together the software and run it</li>
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</ul>
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<h2>Literate (Statistical) Programming</h2>
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<p>An article is a stream of text and code</p>
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<p>Analysis code is divided into text and code "chunks"</p>
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<p>Each code chunk loads data and computes results</p>
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<p>Presentation code formats results (tables, figures, etc.)</p>
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<p>Article text explains what is going on</p>
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<p>Literate programs can be weaved to produce human-readable documents and tagled to produce machine-readable documents</p>
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<p>Literate programming is a general concept that requires</p>
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<ol>
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<li>A documentation language (human readable)</li>
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<li>A programming language (machine readable)</li>
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</ol>
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<p>Knitr is an R package that brings a variety of documentation languages such as Latex, Markdown, and HTML</p>
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<h3>Quick summary so far</h3>
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<p>Reproducible research is important as a minimum standard, particularly for studies that are difficult to replicate</p>
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<p>Infrastructure is needed for creating and distributing reproducible document, beyond what is currently available</p>
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<p>There is a growing number of tools for creating reproducible documents</p>
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<p><strong>Golden Rule of Reproducibility: Script Everything</strong></p>
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<h2>Steps in a Data Analysis</h2>
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<ol>
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<li>Define the question</li>
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<li>Define the ideal data set</li>
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<li>Determine what data you can access</li>
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<li>Obtain the data</li>
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<li>Clean the data</li>
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<li>Exploratory data analysis</li>
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<li>Statistical prediction/modeling</li>
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<li>Interpret results</li>
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<li>Challenge results</li>
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<li>Synthesize/write up results</li>
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<li>Create reproducible code</li>
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</ol>
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<p>"Ask yourselves, what problem have you solved, ever, that was worth solving, where you knew all of the given information in advance? Where you didn't have a surplus of information and have to filter it out, or you had insufficient information and have to go find some?" -- Dan Myer</p>
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<p>Defining a question is the kind of most powerful dimension reduction tool you can ever employ.</p>
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<h3>An Example for #1</h3>
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<p><strong>Start with a general question</strong></p>
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<p>Can I automatically detect emails that are SPAM or not?</p>
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<p><strong>Make it concrete</strong></p>
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<p>Can I use quantitative characteristics of emails to classify them as SPAM?</p>
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<h3>Define the ideal data set</h3>
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<p>The data set may depend on your goal</p>
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<ul>
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<li>Descriptive goal -- a whole population</li>
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<li>Exploratory goal -- a random sample with many variables measured</li>
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<li>Inferential goal -- The right population, randomly sampled</li>
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<li>Predictive goal -- a training and test data set from the same population</li>
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<li>Causal goal -- data from a randomized study</li>
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<li>Mechanistic goal -- data about all components of the system</li>
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</ul>
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<h3>Determine what data you can access</h3>
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<p>Sometimes you can find data free on the web</p>
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<p>Other times you may need to buy the data</p>
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<p>Be sure to respect the terms of use</p>
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<p>If the data don't exist, you may need to generate it yourself.</p>
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<h3>Obtain the data</h3>
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<p>Try to obtain the raw data</p>
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<p>Be sure to reference the source</p>
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<p>Polite emails go a long way</p>
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<p>If you load the data from an Internet source, record the URL and time accessed</p>
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<h3>Clean the data</h3>
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<p>Raw data often needs to be processed</p>
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<p>If it is pre-processed, make sure you understand how</p>
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<p>Understand the source of the data (census, sample, convenience sample, etc)</p>
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<p>May need reformatting, subsampling -- record these steps</p>
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<p><strong>Determine if the data are good enough</strong> -- If not, quit or change data</p>
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<h3>Exploratory Data Analysis</h3>
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<p>Look at summaries of the data</p>
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<p>Check for missing data</p>
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<p>-> Why is there missing data?</p>
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<p>Look for outliers</p>
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<p>Create exploratory plots</p>
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<p>Perform exploratory analyses such as clustering</p>
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<p>If it's hard to see your plots since it's all bunched up, consider taking the log base 10 of an axis</p>
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<p><code>plot(log10(trainSpan$capitalAve + 1) ~ trainSpam$type)</code></p>
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<h3>Statistical prediction/modeling</h3>
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<p>Should be informed by the results of your exploratory analysis</p>
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<p>Exact methods depend on the question of interest</p>
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<p>Transformations/processing should be accounted for when necessary</p>
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<p>Measures of uncertainty should be reported.</p>
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<h3>Interpret Results</h3>
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<p>Use the appropriate language</p>
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<ul>
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<li>Describes</li>
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<li>Correlates with/associated with</li>
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<li>Leads to/Causes</li>
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<li>Predicts</li>
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</ul>
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<p>Gives an explanation</p>
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<p>Interpret Coefficients</p>
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<p>Interpret measures of uncertainty</p>
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<h3>Challenge Results</h3>
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<p>Challenge all steps:</p>
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<ul>
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<li>Question</li>
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<li>Data Source</li>
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<li>Processing</li>
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<li>Analysis</li>
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<li>Conclusions</li>
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</ul>
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<p>Challenge measures of uncertainty</p>
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<p>Challenge choices of terms to include in models</p>
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<p>Think of potential alternative analyses</p>
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<h3>Synthesize/Write-up Results</h3>
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<p>Lead with the question</p>
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<p>Summarize the analyses into the story</p>
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<p>Don't include every analysis, include it</p>
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<ul>
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<li>If it is needed for the story</li>
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<li>If it is needed to address a challenge</li>
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<li>Order analyses according to the story, rather than chronologically</li>
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<li>Include "pretty" figures that contribute to the story</li>
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</ul>
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<h3>In the lecture example...</h3>
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<p>Lead with the question</p>
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<p> Can I use quantitative characteristics of the emails to classify them as SPAM?</p>
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<p>Describe the approach</p>
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<p> Collected data from UCI -> created training/test sets</p>
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<p> Explored Relationships</p>
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<p> Choose logistic model on training set by cross validation</p>
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<p> Applied to test, 78% test set accuracy</p>
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<p>Interpret results</p>
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<p> Number of dollar signs seem reasonable, e.g. "Make more money with Viagra $ $ $ $"</p>
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<p>Challenge Results</p>
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<p> 78% isn't that great</p>
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<p> Could use more variables</p>
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<p> Why use logistic regression?</p>
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<h2>Data Analysis Files</h2>
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<p>Data</p>
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<ul>
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<li>Raw Data</li>
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<li>Processed Data</li>
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</ul>
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<p>Figures</p>
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<ul>
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<li>Exploratory Figures</li>
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<li>Final Figures</li>
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</ul>
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<p>R Code</p>
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<ul>
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<li>Raw/Unused Scripts</li>
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<li>Final Scripts</li>
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<li>R Markdown Files</li>
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</ul>
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<p>Text</p>
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<ul>
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<li>README files</li>
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<li>Text of Analysis/Report</li>
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</ul>
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<h3>Raw Data</h3>
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<p>Should be stored in the analysis folder</p>
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<p>If accessed from the web, include URL, description, and date accessed in README</p>
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<h3>Processed Data</h3>
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<p>Processed data should be named so it is easy to see which script generated the data</p>
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<p>The processing script -- processed data mapping should occur in the README</p>
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<p>Processed data should be tidy</p>
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<h3>Exploratory Figures</h3>
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<p>Figures made during the course of your analysis, not necessarily part of your final report</p>
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<p>They do not need to be "pretty"</p>
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<h3>Final Figures</h3>
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<p>Usually a small subset of the original figures</p>
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<p>Axes/Colors set to make the figure clear</p>
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<p>Possibly multiple panels</p>
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<h3>Raw Scripts</h3>
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<p>May be less commented (but comments help you!)</p>
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<p>May be multiple versions</p>
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<p>May include analyses that are later discarded</p>
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<h3>Final Scripts</h3>
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<p>Clearly commented</p>
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<ul>
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<li>
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<p>Small comments liberally - what, when, why, how</p>
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</li>
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<li>Bigger commented blocks for whole sections</li>
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</ul>
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<p>Include processing details</p>
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<p>Only analyses that appear in the final write-up</p>
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<h3>R Markdown Files</h3>
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<p>R Markdown files can be used to generate reproducible reports</p>
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<p>Text and R code are integrated</p>
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<p>Very easy to create in RStudio</p>
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<h3>Readme Files</h3>
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<p>Not necessary if you use R Markdown</p>
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<p>Should contain step-by-step instructions for analysis</p>
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<h3>Text of the document</h3>
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