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Everything I wish I had known about research design and data analysis… Statlab Workshop Spring 2005 Heather Lord and Melanie Dirks

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Outline of a paper Introduction Theory Data Description Analysis Conclusion

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Introduction TopicQuestion What is the question you want to answer? Review the Literature

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Theory Categorize your theory Descriptive or Causal? Descriptive or Causal? Change over time? Change over time? Write down your theory Identify testable hypotheses from theory Do you need statistics after all? Quantitative v Qualitative research Quantitative v Qualitative research

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Variables Dependent Variable ( response, outcome, criterion) Independent Variables ( explanatory or predictor variables) Control / Confounding Variables Categorical and Continuous Variables Remember: Types of variables we choose, determine the statistics we use

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You need Data Think about analyses early! Collecting your own data Retrospective, prospective, experimental & observational methods Retrospective, prospective, experimental & observational methods Can find most data you’ll need on-line! Statlab Webpage (http://statlab.stat.yale.edu) Advisors Advisors Yale StatCat (http://ssrs.yale.edu/statcat/) Yale StatCat (http://ssrs.yale.edu/statcat/) ICPSR (http://www.icpsr.umich.edu) ICPSR (http://www.icpsr.umich.edu) Reference Librarian (Julie Linden) Reference Librarian (Julie Linden)

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So, you want to make a survey Extensive on-line resources and software Extensive on-line resources and software Question types determine analyses Question types determine analyses Open vs. close ended questions, Likert scales, rank order data Open vs. close ended questions, Likert scales, rank order data Assumptions of normalcy Assumptions of normalcy Validity Validity Internal & External validity Internal & External validity Pilot testing Pilot testing You need variance to analyze! You need variance to analyze! Sample size Sample size It depends; power, effect size, cost (UCLA power calculator) It depends; power, effect size, cost (UCLA power calculator)

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Once You’ve Found or Collected your data Download the data and documentation StatTransfer (Statlab) StatTransfer (Statlab) Determine data file type Probably a text file (.txt,.dat,.raw) Probably a text file (.txt,.dat,.raw) Converting text & delimited files Choose a statistical software program SPSS SPSS

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Managing your data Back up all Master Data Files CDR/CDRW, USB Key Codebook All codes All codes Adding variables, cases, computing new variables Adding variables, cases, computing new variables Keep a roadmap Keep a log of all analyses with what you have done Keep a log of all analyses with what you have done Save syntax files Save syntax files

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Syntax Files What are they? Text-files used to enter commands in bulk Is it worth learning? You will make mistakes, need to make changes SPSS and many other programs let you use pull down menus How do I know what to write? Program’s manual provides the underlying command

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So, how do I analyze my data? Correlational design Correlation allows you to quantify relationships between variables (r, r-squared) Correlation allows you to quantify relationships between variables (r, r-squared) Correlation, partial correlation Correlation, partial correlation Regression allows you predict scores on 1 variable from subjects score on another variable(s) Regression allows you predict scores on 1 variable from subjects score on another variable(s) Group differences t-test & ANOVA t-test & ANOVA Chi-square for categorical and frequency data Chi-square for categorical and frequency data Significance v. effect size

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Descriptive Statistics Variables Dependent Variable(s) Independent Variable(s) Important Control Variable(s) Graphs Summary Statistics on Key Variables Number, Mean, Minimum, Maximum, Standard Deviation Cross-Tabs

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Putting Output into a Paper Cut and Paste Graphs Cut and Paste into Word Processing document Save as.jpeg or.tif file Tables Cut and Paste Format in Word Processing document Import into Excel, format, and then place in Word

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More Advanced Analysis Multivariate techniques help to account for confounding factors, allow for testing change over time and more complex hypotheses … (See: Tabachnick & Fidell, Using Multivariate Statistics) 1) Be honest about your abilities. 2) Ask for help 3) Best off including techniques that you fully understand.

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Take Away Messages 1) Determine your question, methods and statistics before you start 2) Keep a codebook of everything 3) Back up data 4) Ask for help 5) Don’t Get In Over Your Head

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