Learning Objectives

  • Reinforce data scale concepts.

Introduction

Identifying/choosing the correct data scale is key to selecting and performing an appropriate data analysis.

As a group, talk through the following questions and exercises. There’s no assignment to submit, this is just to get you thinking more deeply about data scale.

Data Scales

For each of the scales below, describe the data scale. Ask yourself the following questions:

  • Is it numeric or categorical?
  • Ordinal or nominal?
  • Discrete or continuous?
  • Ratio or interval?
  • Is there a meaningful zero?
  • Are negative and positive numbers allowed?

Pain Scales

Pain is often measured on a scale from 0 (no pain) to 10 ().

What kind of data scale is this?

Temperature Scales

The Rankine temperature scale is related to the Fahrenheit scale in the same way that the Kelvin scale is related to the Celsius scale: a 1-degree increment Rankine is equivalent to a 1-degree increment in Fahrenheit. Unlike Fahrenheit, the Rankine temperature scale has an absolute zero set at 0 degrees, i.e. there are no below-zero temperatures.

0°R is equal to -459.67°F.

  • What kind of scale is Rankine?

Categorical Scales

As a group, think of two categorical data types. One should be nominal the other should be ordinal.

Make sure you can explain why they are different.

Fruit Fly Age

public domain image of D. menalogaster

Drosophila spp. (fruit flies) go through several distinct morphological stages during their lifespan. In a lab setting the D. melanogaster life cycle takes about 50 days.

Describe at least two data scales you could use to quantify the age of individual D. melanogaster flies.

Soil Tension

Soil tension is a measure of how tightly water is held in the soil. High values mean that water is held very tightly, while a value of zero means that the soil is saturated and water can easily be extracted. It is most commonly measured in units of centibars or kilopascals.

It is relevant to plants because they must expend greater energy to extract water when soil tension is high.

  • What kind of data scale would you use to measure soil tension?

Discrete Scales

As a group, hypothesize several scenarios in which a discrete numeric scale would be appropriate.

  • Can you think of a situation where a discrete scale could be treated as approximately continuous?

Circular Scales

One familiar circular scale is aspect, i.e. the direction in which a slope is facing. It is measured in decimal degrees (or sometimes radians).

  • Can you think of any other kinds of phenomena that could be measured using a circular scale?