Observations vs. Inferences

Take a look at the image on the left.  What do you observe?  A pair of eyes?  A nose?  A raccoon?

In reality, the image is a picture of a South African moth using "eye-spot mimicry".  Check out a picture of the moth taken from a different perspective here.  Surprised?

If your instinct was to try to guess what was "in" the image, you are not alone.  It is a very tempting response to the question, "What do you observe?".  However, as scientists, it is important that we understand the difference between what we observe, and what we infer. In this blog post, we will first learn about observations, the types of observations, and the relationship between observations and data.  We will then look into inferences, and how we can use our observations in order to make scientific inferences.

Observations

In reality, an observation is any information you can gather using the five senses and scientific instruments and tools.  In other words, what can we actually see, smell, taste, touch, hear, and measure in the picture?  There are two sets of concentric circles, the colors of burnt red, orange, white, and varying shades of brown, and symmetrical patterns and colors.

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All observations are classified into one of two categories: qualitative observations and quantitative observations.  Qualitative observations describe the characteristics or qualities of something with words, such as color, odor, texture, sound, taste, etc.  Quantitative observations describe the measurement or quantity of something with numbers and a unit of measurement, such as "10 feet" or "150 grams".  Keep in mind that the unit is extremely important; it is the only part of the observation that actually tells us the meaning of that number.

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Qualitative Observations:

• The tomatoes are red.
• The tomatoes are round.
• The tomatoes reflect light.
• The tomatoes have a green vine.

Quantitative Observations:

• The tomatoes have a mass of 15.5 grams.
• There are three tomatoes.
• There are three stems.
• There is one vine.

When a scientist collects data, he/she is simply gathering and recording qualitative and quantitative observations.  Data describes all of the qualitative and quantitative observations that are collected as part of an experiment.  Some experiments involve making more qualitative observations, while others involve making more quantitative observations.  However, most experimental data is a combination of both qualitative and quantitative observations.  For example, scientists who are studying the effects of global warming refer to both qualitative and quantitative data.

Qualitative Observation:  Polar bears live on ice.  This polar bear appears to be clinging on to a melting glacier.

Quantitative Observation: The arctic sea ice has declined since 1979, and has decreased by 1.57 million square kilometers as of 2013.

Inferences

On the other hand, an inference is a logical conclusion based on observations and prior knowledge. "Based on my observations of the tomatoes, I can infer that the tomatoes are fresh because they are bright red, round, and shiny, and have a mass of 15.5 grams, which means that the tomatoes have a reasonably high water content."  In this example inference sentence, note how I incorporated both qualitative observations, quantitative observations, and prior knowledge in the "because" portion of the sentence.  Without this important "because", I would not be fully supporting my logical conclusion (inference).

Let's go back to our first picture example.  I can infer that the object in the image is a winged insect using "eyespot mimicry" because of the symmetrical patterns and colors, concentric circles, and soft appearance.  Again, note how the "because" portion of the inference is where I incorporated my observations and prior knowledge.

Below are example sentences to help you write your own scientific inferences:

• “I infer ___________________, because ________________________."
• “Because _________________, I infer __________________________.”
• “Based on my observations, I infer ________, because _____________.”

Check out the video below, created by Mr. Epp's science classroom.  When watching the video, keep in mind that the word "precise" means accurate and exact.

As scientists, it is very important that we understand the relationship between observations and inferences.  In order to make a scientific inference, we must consider all qualitative and quantitative observations before making any conclusions.  As we move into developing our own scientific investigations this school year, keep in mind that we will be collecting data (qualitative and quantitative observations) to develop our own scientific inferences and explanations of the phenomena we observe.

In-Class Assignment
1.  What is the difference between a qualitative and quantitative observation?
2.  What is data?
3.  What is an inference?
4.  How are observations and inferences related to each other?
5.  Write one scientific inference sentence using the two global warming pictures and observations above (qualitative and quantitative).  Remember to use one of the following sentence formats:

• “I infer ___________________, because ________________________.
• “Because _________________, I infer __________________________.”
• “Based on my observations, I infer ________, because _____________.”

Homework
STUDY your all vocabulary since the beginning of the school year, and your notes on observations, inferences, and cause-and-effect relationships.  Also study the information on the "Cause and Effect: Human Activity and Global Warming", the "Observations vs. Inferences", and "What is Science?" blog posts.  There will be a quiz tomorrow!