Accuracy, Precision, Qualitative, and Quantitative Types Of Measurement Accuracy, Precision, Qualitative, and Quantitative

Types of Measurement Quantitative- uses numbers to describe Examples: 3.25 meters 62 lbs 32°C Qualitative- uses description to describe Extra large Hot Blue

Qualitative or Quantitative? It is hot outside. Yesterday I ran 3 miles. It was 102° outside this afternoon. The balloon was big and blue. The paper felt soft on my skin. I need 3.25mm of string for my project. I am 3 foot 4 inches tall. Wow you’re short!! Quantitative Quantitative Qualitative Qualitative Quantitative Quantitative Qualitative

Scientists Prefer… Quantitative measurements Why do you think that is? Easy to check Easy to agree upon, no personal bias The precision of the measurement device determines the reliability of the value.

How Reliable are the Measurements? Scientists use two word to describe how reliable their measurements are Accuracy- how close the measurement is to the actual value Precision- How close are your measurements to one another or… How well can the measurement be repeated

Differences Accuracy can be true of an individual measurement or the average of several Precision requires several measurements before anything can be said about it Why is that?

Let’s use a golf analogy

Accurate? No Precise? Yes

Accurate? Yes Precise? Yes

Precise? NO Accurate? NO

Accurate? Yes Precise? We cant say!

In Terms of Measurement Three students measure the length of a room to be: 10.2 m 10.3 m 10.25 m If the room is 15.7m Were they precise? Were they accurate? YES NO

Who is More Precise? Which group has the most precise data? Group T How did you decide on that group? Subtract the lowest measurement from the highest measurement for each group. The group with the smallest difference is most precise Group T

Precision of Instrument Precision of Data vs. Precision of Instrument The word precision can also be used to describe how the measurement device (balance, ruler, etc.) being used determines how many decimal places are used when collecting data.

How Many Decimal Places Should I Record? Record a digit for all marks shown on measurement device. The last digit in you data will always be the estimated digit. Using the ruler below we will measure the blue rectangle. The correct length is 2.35 inches The 2 is certain because there is a mark on the ruler The 0.3 is certain because there is a mark on the ruler The 0.05 is our estimated digit because there is no mark for it on the ruler and we must estimate between 0.3 and 0.4

How Many Decimal Places Should I Record? How long is the red rectangle? 5.7 mm The 5 is certain because there is a mark The 0.7 must be estimated between the 5 and 6 mm mark. It is a little more than half way so we estimated 0.7

Proportions Direct Proportions – Dividing one by the other gives a constant value As one value increases the other increases As one value decreases the other decreases They move the same The graph of a direct proportion will be a straight line

Proportions Inverse Proportions – Multiplying one by the other gives a constant value As one value increases the other decreases As one value decreases the other increases They move opposite of one another The graph of a direct proportion will be a curved line