# Thread: Random Variable probability question. Help for a non stastician

1. ## Random Variable probability question. Help for a non stastician

Hi everyone,

I have a stat question.

lets assume I have five possible categories ( 1,2,3,4,5) for a quality issue. since 8 years, a total of 100 products have cat 1, 200 have cat 2, 340 have cat 3, 117 have cat 4 and 50 have cat 5 issues. What is the probability that the next 1000 products will have cat 1 or cat 2 or cat 3 or cat 4 or cat 5 issue?

The yearly figures are not available.

2. ## Re: Random Variable probability question. Help for a non stastician

Your question appears to be poorly framed, and vital information seems to be missing. Are there any products that do not have quality issues of any of the five categories? If so, how many over that same eight-year period?

As to your question, do you mean the probability of the next 1,000 products having any one of category 1 through 5 quality issues? Or do you mean the individual probabilities that all of the next 1,000 products will have a quality issue of the same category for each of the five?

In any case, the only data available are historical and unless there have been changes in the manufacturing process, these data will only yield a best estimate for the desired probabilities.

3. ## Re: Random Variable probability question. Help for a non stastician

hi,
to explain a bit what Con-Tester said:
with this data you can estimate the conditional probability P(A|D) - the probability of a product to belong to category A IF it is defective. The probality of a product belonging to category A is P(A)=P(A|D)*P(D) - so you will need an estimate of P(D) the probability of a product being defective (of any type).

regards

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