Accuracy Precision

% Error

Variable is a factor that affects the outcome of an experiment.

3 Types of variablesExperimental/ Independent Variable

The variable that you change Dependent Variable

The variable that you measureControl Variable

The variables that are controlled or maintained.

Example Lab: Testing to see which plant food helps plants grow the largest? Give Examples of each type of variable in

this lab and check with Mr. Castans

Variable

Accuracy – measure of how close a data point or group of data points are to an accepted value.Accuracy= actual value

If dealing with a group of data, the average must be calculated before checking for accuracy

Give an example of being accurate for the class and check with Mr. Castans

Accuracy

Example:6.54s + 7.01s + 6.99s +6.67s = 27.21s

4 4

6.802s

All of the original measurements were accurate to the hundredths place. Report this accuracy in your final answer.

Round 6.802s to 6.80s.

How to Average…

Precision is a measure of how close replicates are to one another.Precision is picky about it’s group

members!

The precision of data is the usual way in which we evaluate data

Systematic error does not affect precision

Give an example of being precise and check with Mr. Castans

Precision

Type of error that pushes all data in one direction, either too high or too low.

Errors of the apparatus you use to measureExample – Bathroom Scale

Results from either problems with the measuring device or the technique.

Very problematic for experiments because the data looks good.

One way to tell if measurements suffer from systematic error is to measure a standard (something that has a known value)

Example – Measure some weights from a weight room

SYSTEMATIC ERROR MUST BE AVOIDEDCome up with an example for the class and check

with Mr. Castans

Systematic Error

Can be considered the error of estimation and is inherent in all measurements.

Things that affect your measurement such as temperature change, human error, behavior of the material.

About half the data is high and the other half is low. (scattered around the actual value)

Can be corrected for (mostly) by repeating the experiment or averaging the current results.

The average is still accurate The more data points the better. Take several replicates.

Needs to be minimized but since the data is still accurate, it is not too detrimental.

Come up with an example for the class and check with Mr. Castans

Random Error

Percent Error CalculationPercent Error –

Quantitative measure of how accurate data is.

% error describes how well calibrated the measuring device is and how sound the measuring techniques are. ErrorPercent 100%

valueaccepted

valueaccepted valuemeasured

1. If a ruler is misprinted, will the user run into random or systematic error or both? Explain

A - Both. You will run into random error due to your ability to read the ruler. You will run into systematic error due to the misprint. Either all answers will be too short or too long.

2. How accurate will measurements from problem 1 be?

A – Measurements will not be very accurate because the data will either average out high or low.

Practice Problems

3. How precise will measurements from problem 1 be?

A - Measurements may be precise because the values can be close to each other even though they are not close to the actual value.

4. If replicates are not independent of one another, what type of error will be encountered? Explain

A - Systematic error will be encountered because mistakes will be repeated . For example if the ruler is placed incorrectly and not readjusted, the measurements will all be too large or too small.

Practice Problems

5. Draw various X’s on the dartboard below to show what it would look like to be accurate and not precise.

Practice Problems

Your prediction Class prediction

6. A basketball player throws 100 free-throws; 95 of these balls go through the basket; 5 miss the basket entirely. Describe the precision and accuracy of the free-throws.  7. The same player is having an off day; 5 balls go through the basket; the other 95 balls bounce off of the rim. Describe the precision and accuracy of the throws.

Practice Problem