Organizing data in tables and charts: Criteria for effective presentation Jane E. Miller, Ph.D. Rutgers University About the author Author: The Chicago Guide to Writing about Multivariate Analysis (Chicago, 2005) and The Chicago Guide to Writing about Numbers (Chicago, 2004), and other articles about statistical literacy and quantitative communication. Professor, Rutgers University Institute for Health, Health Care Policy and Aging Research. Edward J. Bloustein School of Planning and Public Policy. Learning objectives To learn the different types of variables and how they affect choices for organizing data. To become aware of different principles for organizing variables in tables or charts. To learn the strengths and weaknesses of tables, charts, and prose for organizing and conveying numeric information. Performance objectives To be able to choose among different criteria for organizing data for a particular task. To be able to identify whether to use a table or chart to present data for a specific objective. To understand how to write a prose description to coordinate with a table or chart. Why does order of variables matter? The arrangement of items in a table or chart should coordinate with order they are mentioned in the prose description. Avoid zigzagging back and forth across a chart or among rows and columns of a table. Usually describe a pattern based on observed numeric values, e.g., most to least common. Often a hypothesis includes some theoretical basis of how items relate to one another. Ordinal and continuous variables Values of ordinal, interval, and ratio variables have an inherent numeric order. E.g., age groups, dates, blood pressure. Numeric or chronological order of values is the principle for organizing those values in a table or chart. Nominal variables Values of nominal variables have no inherent numeric order. E.g., categories of race, gender, or region. Need an organizing principle to determine sequence of items. Same issue if you have >1 variable to present. Several different causes of death. Prevalence of >1 symptoms, attitudes, etc. + and - of different tools Strengths Prose Table Chart Easiest way to explain patterns Holds lots of #s Good for detail Predictable structure Holds lots of #s Easy to see general patterns Predictable structure Weaknesses Hard to organize a lot of numbers Harder to "see" patterns Difficult to see specific values Complementary use of prose, tables & charts Use tables and charts to present full set of numeric values. Use prose to describe the pattern or address the hypothesis. Use same ordering principle in table or chart and its accompanying prose. Improves clarity of narrative line. Prose description of a pattern Objectives: Describe size and shape of the pattern. Explain whether it matches hypothesis. Specify direction and magnitude of association. Direction: “Which is higher? Magnitude: “How much higher?” Direction for different types of variables Direction for ordinal, interval or ratio variable: Is the relationship positive, negative, or level? E.g., as income rises, do death rates increase, decrease or remain constant? For nominal variables: Which category has the highest value? E.g., which gender has the higher death rate? Principles for organizing data Alphabetical order Order of items on original data collection instrument Empirical order Theoretical groupings Arbitrary order – NEVER a good idea! Think about how the data will be used, and choose one of the above principles! For tables and charts accompanied by prose Pattern description or hypothesis testing Example: Attitudes about legal abortion “Please tell me whether or not you think it should be possible for a pregnant woman to obtain a legal abortion” If the woman wants it for any reason If there is a strong chance of defect in the baby If the woman's own health is seriously endangered by the pregnancy If she is not married and does not want to marry the man If she becomes pregnant as a result of rape If she is married and does not want any more children From the 2000 U.S. General Social Survey % of respondents who agree 43.7 79.8 88.2 42.5 80.8 44.4 Order of items from questionnaire % of respondents Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey 100 80 60 40 20 0 Any reason Defect in Wants no Mother's Pregnant baby more kids health due to rape Not married Order of items from questionnaire % of respondents Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey 100 80 60 40 20 0 Any reason Defect in Wants no Mother's Pregnant baby more kids health due to rape Not married Alphabetical order Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey % of respondents 100 80 60 40 20 0 Any reason Defect in Mother's baby health Not married Rape Wants no more Empirical order (descending) Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey % of respondents 100 80 60 40 20 0 Mother's health Rape Defect in Wants no baby more Any reason Not married Theoretical grouping Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey % of respondents 100 80 60 40 20 0 Mother's Pregnant Defect in health* due to baby* rape* Health reasons Wants no more kids Any reason Not married Social reasons Theoretical grouping Agreement with legal abortion under specified circumstances, 2000 U.S. General Social Survey % of respondents 100 80 60 40 20 0 Mother's Pregnant Defect in health* due to baby* rape* Health reasons Wants no more kids Any reason Not married Social reasons ut Ap il it pa ie s re la F oo nd se d rv ic Pe es Tr rs on an s al i n p or s t & at io Al p l o en n si th er ons ho u H ea sin En l th g ca C as t ert ai re h co nm nt e ri b nt M isc ut io ns el la ne Ed ou uc s P Al e co rso at io n ho n lic a l c To a b ba e ve re cc ra o ge pr od s uc t R ea s di ng Sh el te r+ Combining theoretical & empirical criteria Descending dollar value of expenditures for necessities and non-necessities, 2002 U.S. Consumer Expenditure Survey $15,000 $12,000 $9,000 $6,000 $3,000 $- Necessities Non-necessities Pattern with a third variable % of respondents Agreement with legal abortion, by gender of respondent and circumstances of abortion, 2000 U.S. General Social Survey Organized by topic of abortion question 100 Men 80 Women 60 40 20 0 Mother's Pregnant Defect in health* due to baby* rape* Health reasons Wants Any no more reason kids Not married Social reasons * difference between men and women is statistically significant at p<.05 Pattern with a third variable % of respondents Agreement with legal abortion, by gender of respondent and circumstances of abortion, 2000 U.S. General Social Survey Organized by topic of abortion question 100 Men 80 Women 60 40 20 0 Mother's Pregnant Defect in health* due to baby* rape* Health reasons Wants Any no more reason kids Not married Social reasons * difference between men and women is statistically significant at p<.05 Identifying theoretical criteria Consult the published literature on your topic to learn about theoretical criteria for organizing your variables. In new research areas, empirical sorting may yield clusters with similar response patterns that can then be explored for conceptual overlap. For self-guided data lookup Why is it important? When is it used? Researchers look up data for own research questions, then organize the data using empirical or theoretical criteria. How to organize data for such tasks? Alphabetical order Order of items from data collection instrument Standard ordering used in periodic reports Alphabetical order Widely familiar principle, e.g., used in Phone book Daily stock market report Learned at an early age Facilitates self-guided lookup Ordering for a public data source Order of items on original data collection instrument Users can refer to codebook Easy to find the variables they need Ordering used in periodic reports Standardized topic from year to year for a given Summary There is no one principle for organizing numeric data that fits all possible tasks. Determine your main objective Hypothesis testing or pattern description Data reporting for others’ use Choose the organizing principle accordingly.