Question

Do variance and variability have the same effect on manufacturing system performance measures of throughput, production rate and cycle time?

Answer 1

Variability means how much data is spread out from the mean. If variability is more, the data is more spread out

Variance means how close the values are to the mean of the data. It is the deviation from the mean

Both variation and variability have different impact on performance measures.

Example: There are 5 employee and the average throughput is 10 units per hour.

Throughput for each employee is as:

1 = 8 per hour

2 = 9 per hour

3 = 10 per hour

4 = 11 per hour

5 = 12 per hour

In such a case, the variability is high and spread out. But variance for the system is 0 as positive variance is negated by negative variance from mean. So, there is no variance and only variability in the process

Similar is the case for cycle time and production rate.

Hence, both are essential for performance measure as high variability will increase the standard deviation for the process and data will be spread out. Variance may or may not be there basis the spread of data. Ideally, Variance should be zero for system.