Accuracy Precision % Error

Variable is a factor that affects the outcome of an experiment. 3 Types of variables Experimental/ Independent Variable The variable that you change Dependent Variable The variable that you measure Control Variable The variables that are controlled or maintained.

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

Example: 6.54s s s +6.67s = 27.21s s All of the original measurements were accurate to the hundredths place. Report this accuracy in your final answer. Round 6.802s to 6.80s.

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

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

Can be considered the error of estimation and is inherent in all measurements. About half the data is high and the other half is low. (scattered around the actual value) The average is still accurate The more data points the better. Take several replicates. Needs to minimized but since the data is still accurate, it is not too detrimental.

Percent Error – Quantitative measure of how accurate data is. % error describes how well calibrated the measuring device is and how sound the measuring techniques are.

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.

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 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.