Units of Analysis and data structure

The Basics

Outline

Definitions

Elements of the unit of analysis

Data structure

Unit of observation

The unit of observation is a basic concept in quantitative research that represents the objects that are observed and about which information is systematically collected.

Unit of analysis

The unit of analysis is the object about which generalizations are made based on an analysis.

Determination

The unit of observation is determined by the method by which observations have been selected;

The unit of analysis is determined by an interest in exploring or explaining a specific phenomenon.

When they are the same

The unit of observation and unit of analysis are the same when the generalizations being made from a statistical analysis are attributed to the unit of observation.

Identifying units of analysis

The unit of analysis is shaped by three properties:

Social entities

Time

Space

Social entities

observations of a single social entity, such as a person or an institution

observations of multiple entities with a defined relationship, such as family, employer-employee

Social Phenomena

transactional observations that are the result of actions among entities, such as labour strikes or international conflicts, including wars.

Time

observations made at one point in time: a cross-sectional study

Time

observations made at multiple points in time

the data may be organized by time; commonly referred to as a time series

time may structure some form of repeated measures of content or subjects

Space

observations made within a specific spatial area

observations made within a hierarchy of spatial areas

Substituting units

There may be requests for which data for a desired unit of analysis can’t be delivered but for which data are available summarized over one of the other attributes of the unit of analysis.

Substituting units

Example:

Request for firm-level data for NAICS 312 Beverage and Tobacco Product Manufacturing

Ideal source: microdata on establishments from the Canadian Census of Manufacturers

No access to enterprise microdata

Substituting units

Example: NAICS 312

Alternatives: are there aggregate data summarizing the firms within NAICS 312?

Possibilities: summaries over time (time series) or geography (small-area business statistics)

Statistical data structure

Let’s review basic data structure.The unit of analysis defines the underlying structure of a data file.

This structure consists of a series of rows with each row containing the data of one member of the unit of analysis.This simple structure is known as the flat, rectangular data matrix.

Statistical data structure

Case 1

Case 2

Case 3

*

Case n

*

*

Case n-1

Statistical data structure

Statistical data structure

All of the information collected for each member of the unit of analysis is organized in a fixed location in the file called fields or variables.

Case 1

Case 2

Case 3

*

Case n

*

*

Field 1*Field2

Field 3* Field k-1

Field k

Case n-1

Statistical data structure

Case 1

Case 2

Case 3

*

Case n

*

*

Field 1*Field2

Field 3* Field k-1

Field k

Case n-1

Statistical data structure

Statistical data structure

This structure looks like the grid of a spreadsheet. However, there is one very important difference between a statistical data structure and a spreadsheet.

The spread sheet is organized around individual cells, while the statistical data structure is organized around the rows.

Spreadsheet

Statistical data structure

Cell B2

Cell E3

Cell C5

Cell F7

Spreadsheet

Statistical data structure

Statistical Data Structure

Row 1

Row 3

Row k-1

Statistical data structure

Statistical data structure

The next slide presents the way that this simple statistical data structure appears in SPSS.

Row 1

Row 1

Row 8

Row 1

Row 8

Row 15

Row 1

Row 8

Row 15

Field 8