Errors in Measurement BIAS The measurement is always

Errors in Measurement

BIAS The measurement is always over or under the true value of the property measured. How can these items show bias?

1. If you weigh yourself right before going to every doctor’s appointment and it says two pounds lighter than the doctor’s scale every time, that’s a biased scale. 3. The temper a gauge on the ture oven is broken a degree nd runs 25 s actuall over what it y is. If yo remem ber this u don’t it when and ad just you pu t someth in will bur g in the oven n ever , it y time. 2. If your mom sets your alarm clock 15 minutes early every morning so you are not late to school (without your knowledge), this is a biased measurement. You think it takes you a certain amount of time, and you are actually finishing 15 minutes early.

RANDOM ERROR O If an object is measured several times with the same instrument and different results are obtained each time. O In the construction industry, the saying “measure twice, cut once” refers to a random error prevention technique.

Another way random error often happens: EYEBALLING The art of saying “that looks about right” or “that looks the same” creates some of the greatest random error.

RELIABILITY Results are Repeatable Measurement s are found to have small/no random error Results are Reliable

Reliability and Bias hmm… If a measurement is biased, it is also reliable, as it is off by the same amount each time. This makes it a repeatable measurement.

Y T I L I B A I REL O The average of several repeated measurements is more reliable than a single measurement. O This will allow for any one random error in measurement to be observed, if possible.

Group Work #6 O Write two different scenarios: Identify ways that validity, bias, reliability, and random error can be involved. Remember, nothing can be perfect. O For example: Baking cupcakes — O using a microwave oven is usually an inappropriate instrument (validity – temperature and time will be affected with an inappropriate instrument) O oven runs 25° hot and tends to burn contents every time if forgotten (bias and reliability – happens each time and by the same amount) O box instructs to fill cups 2/3 full. Each cup is filled differently due to spooning (random error – they will be different sizes, some will be overcooked, others cooked correctly, rest may be undercooked)