Types of Variables



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Types of Variables
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Unit 3

Discuss what potential ethical issues relate to a research topic that you would like to investigate. What are the ethical issues, and how would you approach them? What are your plans for taking formal research ethics training?


Unit 6

After reading the lesson and section 29.2 in the textbook, describe the variables (e.g., ratio, interval, ordinal/ranked, nominal/categorical binomial) that will be used in your research project.

29.2Types of Variables

variable is a characteristic that can be assigned to more than one value. Examples of variables that could be examined during a population health study include age, sex, annual income, languages spoken at home, frequency of alcohol ingestion, cholesterol level, history of chickenpox, and use of contact lenses. The value of a variable for an individual does not have to vary over time, but the response among individuals within a population should be something that might differ.

In most statistical analysis software programs, responses from individual participants are displayed in the rows of a data table and each column represents one variable. If one column presents the data for sex, one value for sex—such as an F or 0 for females or an M or 1 for males—will be listed in each row of that column. Another column may represent age in years, and one value for age—usually a whole number—will be listed in each row.

There are several ways to classify variables (Figure 29-2).

  • ratio variableis a numeric variable that can be plotted on a scale on which a value of zero indicates the total absence of the characteristic. For example, if height is measured in feet, a measurement of 0 feet tall means there was no height. As a result, the ratio of heights is meaningful. A person who is 6 feet tall is twice as tall as a person who is 3 feet tall, yielding a ratio of 2 to 1.
  • An interval variableis a numeric variable for which a value of zero does not indicate the total absence of the characteristic. An outside temperature of 0°C does not mean there is no heat. If the weather turns colder, the temperature may fall to –10°C or lower. A day with a high temperature of 40°F is not twice as hot as a day with a maximum temperature of 20°F.
  • An ordinal variable, also called a ranked variable, is a variable with responses that span from first to last, from best to worst, from most favorable to least favorable, or from always to never, or that are expressed using other types of ranked scales. (Figure 21-4provides examples of other types of ranked responses.) The rank order can be assigned a number. For example, the responses to a survey that asks participants to indicate their level of agreement with a statement can be coded with agree as “3,” neutral as “2,” and disagree as “1.” Alternatively, responses could be coded with agree as “1” and disagree as “3,” or neutral could be set as “0,” agree as “1,” and disagree as “–1.” No matter whatthe scale is, the order of the responses is indicated by their numeric values.
  • nominal variable, also called a categorical variable, has values that represent no inherent rank or order. For example, there is no obvious way to numerically rank the favorite recreational sports activities of participants or their blood types. A dichotomous variableis a subtype of categorical variable with only two possible answers. A binomial variableis a dichotomous variable that has been coded as having values of only “0” and “1,” such as coding yes as 1 and no as 0 or coding adults as 1 and children as 0.
  • FIGURE 29.2Types of Variables
Variable Type Definition Examples
Ratio Numbers on a scale for which zero indicates the complete absence of the characteristic Blood pressure, height, weight
(The ratio of 20 kg to 10 kg is meaningful because the weight doubles when it increases from 10 kg to 20 kg.)
Interval Numbers on a scale for which zero does not indicate the complete absence of the characteristic Temperature (°F or °C) (The heat does not double if the temperature increases from 20° to 40°, because 0° does not represent the absence of all heat.)
Ordinal/ranked An ordered series that assigns a rank to responses (from first to last in the series) but for which the numbers assigned to the values are not meaningful Highest educational level completed, scales for never (1) to always (5), scales for strongly disagree (1) to strongly agree (5)
Nominal/categorical Categories with no inherent rank or order Employment sector, blood type
Binomial Categorical variables for which only two responses are possible yes/no, male/female, case/control
  • Ratio and interval variables can be further classified as either continuous variables or discrete variables. A continuous variableis a numeric variable that can take on any value within a range. For example, although height is often rounded to the nearest inch when it is measured, a person’s height could actually be 59½ inches or 68¾ inches or 77.1529 inches. A discrete variable is a numeric variable that is not continuous. Discrete variables often are generated by counting items, so there are gaps between the acceptable values. For example, a family can own 2 egg-laying chickens or 17 chickens, but cannot own 2½ chickens or 5¼ chickens.


Unit 7

After reading the unit lesson and the required unit resources, post your abstract in the discussion board and discuss why you chose this topic and how it relates to research you plan to continue or to your future career.


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