# S2 Hypothesis Testing - Why 'as bad or worse'?

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

I will preface this by apologising if this is a stupid question.

From the Edexcel textbook:

Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

From the Edexcel textbook:

*The phrase 'as bad or worse' is sometimes helpful. We calculate the probability of getting evidence as bad or worse than that we have been presented with to make our judgement.*Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

0

reply

(Original post by

I will preface this by apologising if this is a stupid question.

From the Edexcel textbook:

Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

**petrus123**)I will preface this by apologising if this is a stupid question.

From the Edexcel textbook:

*The phrase 'as bad or worse' is sometimes helpful. We calculate the probability of getting evidence as bad or worse than that we have been presented with to make our judgement.*Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

0

reply

Report

#3

(Original post by

I will preface this by apologising if this is a stupid question.

**petrus123**)I will preface this by apologising if this is a stupid question.

From the Edexcel textbook:

Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

*The phrase 'as bad or worse' is sometimes helpful. We calculate the probability of getting evidence as bad or worse than that we have been presented with to make our judgement.*Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

The basic problem is that if you are dealing with continuous probability distributions, then P(X = a) = 0 for any singleton value a. Since you are basing your hypothesis test on an observed value a, and you really would like to come out with a meaningful probability statement about a being observed, this is a problem!

The trick that is used in frequentist statistics is to say that you want to calculate the probability of a value equal to, or more extreme than, a being observed. This is, to some extent, arbitrary. You could equally calculate the probability of a value being observed within any interval around a - but the question then arises about how you choose that interval and how you interpret the probabilities that pop out. So, that's the convention that has become established and what we're used to using.

1

reply

Report

#4

**petrus123**)

I will preface this by apologising if this is a stupid question.

From the Edexcel textbook:

Why it is collective? Why do we calculate, for example, P(X<=1) rather than just P(X=1)?

1

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top