Survey Methodology Data interpretation and presentation

1. Survey MethodologyData interpretation and presentation EPID 626 Lecture 11

2. References • Many elements of this lecture were taken from • Fink, Arlene. How to Report on Surveys. Sage Publications. 1995. • Babbie, Earl. Survey Research Methods. Wadsworth Publishing Company. 1990.

3. Analytic modes • Univariate analysis • Examination of the distribution of cases on only one variable at a time • Aim is description • Example: SBP distribution among subjects • Bivariate analysis • Examination of the distribution of cases on one dependent and one independent variable • Aim is explanation • Example: SBP distribution by sex

4. Analytic modes (2) • Multivariate analysis • Examination of the distribution of cases on one dependent and more than one independent variable • Aim is explanation • Example: distribution of SBP by race and sex

5. Presenting univariate data Options (example=age): • List all respondents with their age • Tabulate the number of respondents within categories of age • Use measurements of central tendency and dispersion • Appropriate for continuous data

6. Measures of central tendency • Mean • Average • Mode • The most frequent attribute • Median • The middle attribute in a ranked distribution of observed attributes

7. Measures of dispersion • Range • Distance between the lowest and highest values • Often presented as min and max • Example • range= 40 • or range= 20-60 • Standard deviation • Distribution of observations about the mean

8. Measures of dispersion (2) • Quartile deviation or semi-interquartile range • One-half of the distance between the bottom of the first quartile and the top of the fourth quartile

9. Constructing bivariate tables • Column headings are determined by the most important comparison • cases vs. controls, men vs. women etc. • There are many options for format; decision should be made based on ease of interpretation

10. Guidelines for formatting tables • Headings or titles should sufficiently describe what is in the table • The original content of the variable (the survey question) should be presented in the table or in accompanying text • Values or categories of each variable should be indicated

11. Guidelines for formatting tables (2) • When presenting percentages, the base upon which they are computed should be indicated • Number of respondents with missing data should be indicated • If appropriate, statistical values (frequencies or percents) should be in descending order

12. Example

13. Guidelines for formatting tables (3) • Use a standardized set of symbols to call the reader’s attention to key aspects of the table • definitions • statistical significance • different denominator for % • P-value format • use “=“ for exact p-value • use “<“ for other p-values

14. Presenting data “First you tell’em what you’re gonna tell’em, then you tell’em, then you tell’em what you told’em, and then you tell’em what to do with it.” -Preacher’s proverb

15. Presenting data • A reader should be able to replicate your study • Data without methods is meaningless • A reader should be able to verify all percents and measures of association such as OR or RR

16. Interpretation of results • Interpretation should follow the flow from your research question and study objectives • Interpretation should be guided by statistical significance as appropriate