Question

Question 5 options:

After weighing 25 microliters and 190 microliters (each in triplicate) with a P200, you found out that the standard deviation was smaller for the high volume measurements as compared to the lower ones. Therefore you would assume that your pipette is more accurate in its _________________ working range.

Answer 1

Ans. Standard deviation is a measure of deviation from the means of given values.

Consider following two cases in which two students weighed the same 100.0 g object separately-

Case 1: Three reading = 99.0 g, 100.0 g, 101.0 g g

            Mean = 100.0           ; SD = 1.0

Case 2: Three reading = 97.0 g, 100.0 g, 103.0 g g

            Mean = 100.0           ; SD = 3.0

Both the cases have same mean, but case 2 has higher value of SD.

It is because greater is the deviation of the measurements from mean, greater would be the resultant SD. That is, a larger value of SD means greater extent of deviation from mean or less accuracy in measurements.

Alternatively, a smaller SD value indicates that the measurements have little difference from the mean, and the measurements are recorded more accurately.

Now, coming to the question:

After weighing 25 microliters and 190 microliters (each in triplicate) with a P200, you found out that the standard deviation was smaller for the high volume measurements as compared to the lower ones. Therefore you would assume that your pipette is more accurate in its higher working range

# Lower SD value for higher volume means that the measurements in higher range are relatively more closer to the mean value; so, the pipette deliver higher volumes more accurately.