Collecting Data Samples
As it is difficult most of the time to collect data of the entire population of the subject in interest, randomly sampling from the population is important in Six Sigma for teams to draw conclusion from the sampled data that is representative of the entire population.
To ensure samples can be used to draw statistical conclusions, the sampling must be handled correctly and appropriately sized.
Types of Sampling Strategies
Simple Random Sampling
Simple random sampling works when there is an equal chance that any item within the population will be chosen.
Random sampling requires that the sample represents similar attributes and percentages as the entire population.
Stratified Sampling
Stratified Sampling occurs when the population as a whole is divided or can be divided into subgroups with different attributes.
For example, when sampling the Voice of Customers for headphone products of a company, the sampling grouped by age groups and demographic would be essential for the company to understand the real feedbacks of the product better.
Sequential Sampling
Sequential sampling involves selecting every X item for inclusion in the sampling. Sequential sampling can be used when teams are collecting data at intervals such as time.
For example, in a outgoing delivery operation in a warehouse, the operator might take a sample inspection of delivery details on the label against the details in the system to ensure the accuracy of the delivery in interval of every 15 minutes. In this manner, the error of labelling would provide information on trends of when the most occurrence happened.
