1 Types and Sources of Data UAPP 702 Research Methods for Urban & Public Policy Based on notes by Steven W. Peuquet, Ph.D.

2 Distinction between DATA and INFORMATION  DATA is the raw material of information.  may be adequate to provide the information needed, or it may be partially adequate, or may be useless.  INFORMATION is very useful and contributes in significant ways to answering one or more of a researcher’s research questions.

3 Types of Data Cross-Sectional Data Longitudinal data  Trend data (time series)  Cohort data  Panel data

4 Primary Data  data that was collected for the expressed purpose of answering a specific research question or set of related research questions.

5 Secondary Data  was not collected for the expressed purpose of answering a current specific research  probably collected by persons other than those involved in the current research project  probably has been archived for some period of time in some form

6 Types of Data Cross-sectional data  the measurement of variables for a sample drawn from a selected universe of units of observation (people, objects, social artifacts, etc.)  obtained at one point in time (or during a relatively short period of time)  a “snapshot” of that universe Examples:  US. Census of Population & Housing done in 2000  Survey we took in class  Poll taken before an election

7 Types of Data (2) Longitudinal: trend data (time series)  consists of two or more cross-sectional “snapshots” taken at different times  definition of the universe of units of observation and the variables measured remain the same…but…  the specific units of observation included in each sample differ  due to the use of random selection and  changes in the specific units that meet the definition for being members of the universe. Examples  US. Census of Population & Housing done in 1970, 1980, 1990,  Multiple surveys in class done every week concerning whether the U.S. should enact universal health care  Poll taken once a week every week during the two months leading up to an election

8 Types of Data (3) Longitudinal: cohort data (time series)  consists of two or more cross-sectional “snapshots” of a specific subpopulation (cohort) taken at different times  where the actual units of observation making up the subpopulation (cohort) and the variables measured remain the same, but…  the specific units of observation actually included in each sample differ due to the use of random selection.  members of a subpopulation (cohort) are “followed” as a group over time Examples  Data on how attitudes about war changed over time for soldiers who are Viet Nam veterans.  Data on changes in math proficiency of children who began taking a new math curriculum in the Middleburg School District in the 3 rd grade.

9 Types of Data (4) Longitudinal: panel data  Consists of two or more measurements taken  for the exact same units of observation and variables  at two or more different points in time Examples  Study by the U.S. Bureau of the Census on the impact of welfare reform on specific welfare mothers and their children over a period of 5 years  Study of how the attitudes of specific students in UAPP 800 changed during the Fall 2002 semester regarding their views about the U.S. going to war against Iraq  Study of how potential voters’ preferences for different candidates changed over a 6 month period leading up to the election for governor.

10 Secondary Data Sources  Raw, tabulated, or aggregated statistical data from government, industry or special interest groups (e.g., U.S. Bureau of the Census)  Journals and books  Magazines and newspapers  Internet and the World Wide Web  Administrative or other records

11 Problem of Fit  Must always be concerned about a good fit between secondary data and the research question…  because the data was not developed and structured for the specific purpose of answering the current research question(s)  So…two options…  Find the data to answer the question(s), which might require that primary data be collected also, or  Change the research question(s) so that it (they) can be answered by the data you have.

12 Problem of FIT (continued) “Story of the Man Who Lost his Keys”

13 Benefit of Secondary Data  determining what secondary data is available helps the researcher determine what primary data needs to be collected.  maximum use of secondary data minimizes expenditure of time, effort and money.  general rule of thumb is:  least expensive: secondary data (cross-sectional or longitudinal)  more expensive: primary cross-sectional data  most expensive: primary longitudinal data

14 Disadvantages of Secondary Data  Data may be old  Concepts not defined and operationalized in an ideal manner  e.g., definition of what constitutes "drug abuse”  Not best unit of observation  e.g., use of "household" instead of "family”  Data has been aggregated, hence, data records for each observed unit not available

15 Evaluating Secondary Sources  data collection is usually "purposeful,"  and the purpose for why the data was collected can influence  the data collection procedure employed  the definition of terms and categories  the quality of the information  the conclusions drawn

16 Evaluating Secondary Sources (2) Key questions to ask about a given secondary data source...  What was the purpose of the study?  Why was the information collected?  Who was responsible for collecting the information?  What qualifications, resources, and potential biases are represented in the conduct of the study?  What information was actually collected?  How were units and concepts defined?  How direct were the measures used?  How complete was the information?

17 Evaluating Secondary Sources (3) More key questions...  When was the data collected? Is the information still current, or have events made the data obsolete?  Were there specific events occurring at the time the data were collected that may have produced the specific results obtained?  How was the data obtained? What was the methodology employed?  How consistent is the data obtained from one source with information obtained from other sources?

18 Secondary Data Resources There are numerous sources of secondary data.  U.S. Bureau of the Census (  U.S. Census “American FactFinder” (  U.S. Federal Government (  University of Delaware Library Data Bases (  Center for Applied Demography and Survey Research, University of Delaware (  State of Delaware (  Inter-University Consortium for Political and Social Research (  Social Sciences Data Services, Northwestern University Library (

19 Secondary Data & Literature Review  A literature review for a research project can be thought of as “secondary” in nature…  because the literature was not done for purposes of supporting your current research project.  literature is critical to applied social and policy research because it is…  critical to the formulation and refinement of the research question(s) by helping to identify gaps in knowledge  provides context for new research