Levels of measurement

• Explanation: The nominal level of measurement involves categorizing data into distinct, unordered categories. The different countries are simply labels; there is no inherent ranking or order between them. One country is not "more" or "less" than another in terms of this variable itself. The numbers or codes assigned to each country are arbitrary identifiers and do not represent any quantitative value or order.

2. Ordinal Level of Measurement

• Research Article: "The Relationship Between Socioeconomic Status and Perceived Health: A Systematic Review" by Deaton, Angus. Health Economics, 2002, 11(1), 1-26.

• Example: The variable "Socioeconomic Status (SES)" is often measured at an ordinal level in many studies, including those reviewed in this article. Researchers might categorize SES into groups like "Low," "Medium," and "High."

• Explanation: The ordinal level of measurement involves categorizing data into ordered categories. In this example, "High" SES is understood to be greater than "Medium," which is greater than "Low." However, the intervals between these categories are not necessarily equal or quantifiable. The difference in socioeconomic status between "Low" and "Medium" might not be the same as the difference between "Medium" and "High." The categories indicate a relative ranking but not the magnitude of difference.

3. Interval Level of Measurement

• Research Article: "Body Mass Index and Mortality Among Adults with Incident Type 2 Diabetes: A Prospective Study" by Gregg, Edward W., Ping Zhang, Yiling J. Cheng, Frank B. Hu, Walter C. Willett, Graham A. Colditz, and K. M. Venkat Narayan. Annals of Internal Medicine, 2005, 143(11), 793-800.

• Example: The variable "Body Mass Index (BMI)" is measured at the interval level. BMI is calculated using weight and height, resulting in a continuous numerical value (e.g., 25.5, 30.1, 19.8).

• Explanation: The interval level of measurement involves data that can be ordered, and the intervals between the values are equal and meaningful. For example, the difference in BMI between 25 and 30 is the same magnitude as the difference between 30 and 35. However, the interval level lacks a true zero point. A BMI of 0 does not signify the complete absence of body mass in a biologically meaningful way; it's a theoretical point below what is physically possible for a living human. Ratios are not meaningful at the interval level (e.g., a BMI of 30 is not "twice" as much body mass as a BMI of 15 in a direct proportional sense).

4. Ratio Level of Measurement

• Research Article: "The Impact of Maternal Education on Child Mortality in Sub-Saharan Africa" by Mensch, Barbara S., Wendy D. Baldwin, and Martha A. Koenig. Population Studies, 1993, 47(1), 1-15.

• Example: The variable "Number of Years of Maternal Education" is measured at the ratio level. This variable can take on values like 0, 6, 10, or 16 years.

• Explanation: The ratio level of measurement possesses all the characteristics of the interval level (ordered categories, equal intervals) and also has a true and meaningful zero point. Zero years of maternal education signifies the complete absence of formal schooling for the mother. Because of this true zero, ratios between values are meaningful. For example, a mother with 10 years of education has twice as many years of education as a mother with 5 years of education. Variables like income, height, weight, and age are also typically measured at the ratio level.

It is important to note that the level of measurement for a particular concept can sometimes vary depending on how it is operationalized in a specific study. Researchers make decisions about how to measure their variables based on their research questions and the data they are collecting.

Finding four specific research articles that neatly demonstrate all four levels of measurement within the same study can be challenging, as researchers often focus their measurement strategies based on the variables they are investigating. However, I can provide four distinct research articles, each showcasing a clear example of one of the four levels of measurement. For each article, I will:

• Provide the citation (or enough information to locate it).
• Identify an example of the specific level of measurement.
• Explain why that level of measurement applies.

1. Nominal Level of Measurement

• Research Article: "Gender Differences in Political Participation: Evidence from 50 Countries" by Paxton, Melanie, Joni Lovenduski, and Matthew Hughes. Political Studies, 2007, 55(4), 868-893.

• Example: The variable "Country" in this study is measured at the nominal level. The researchers categorize political participation data based on the country from which it was collected (e.g., Kenya, United States, France).