Question

PLEASE HELP!

The manager of a sawmill wants to find out what percentage of the boards that the mill produced are defective.

Which sampling methods are likely to be biased?

Select each correct answer.


The manager selects 20 boards at random each day for 5 days and examines them.

Every 40th board produced over the course of 1 week is selected and examined.

On 1 day, an hour after the sawmill begins production, 30 boards in a row are selected and examined.

The manager sends an email to 20 customers who buy lumber from the mill, asking each how many of the boards they bought the past week were defective. Results from the first 5 customers to respond are tallied

Answer 1

C,D

Explanation:

Answer 2

The last two methods listed are likely to be biased.

The third one, sampling 30 boards in a row an hour after production starts, does not take a very large sample. Additionally, if something in the machinery is defective only later in the day, the data will be misleading. Similarly, if the machinery is only faulty until it "warms up," the data will be misleading.

The last method, the voluntary survey, is likely to only get responses from people that feel very strongly one way or the other about their product. Choosing only 5 responses from this is also not the best choice, as that is an extremely small sample.