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Thread: Significance Test: Ho & Ha

  1. #1
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    Significance Test: Ho & Ha

    Me again This is a long assingment I'm working on, and I have another question that I'm doubting my answer on.... This is the question:


    Tracking the placebo effect. The placebo effect is particularly strong in patients with Parkinsonís disease. To understand the workings of the placebo effect, scientists made chemical measurements at a key point in the brain when patients received a placebo that they thought was an active drug and also when no treatment was given. They hoped to find that the placebo reduced the mean response. State Ho and Ha for the significance test.

    This is my take (I'm having a hard time grasping this whole Ho & Ha concept)

    From what I understand, the Ho is what you don't want to happen, and in this case you don't want the placebo to not have an effect. So my Ho is:

    Ho: there will be no difference

    And from what I understand, the Ha is what you think will happen, and in this case you want there to be a difference between the groups, and that difference is that the placebo will reduce the mean chemical brain response. So my Ha is:

    Ha: the placebo will reduce the mean chemical brain response

    Is there a sort of equation way to write this? Or is it supposed to be written out in words when no numbers are provided?

    Perhaps something like:

    Ho: placebo = control
    Ha: placebo (the 'does not equal' symbol thingy... the = with a / thru it ) control

    Am I anywhere close with this?!

    Thanks SO SO much in advance. I'm very glad to have found this site! It's awesome!

  2. #2
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    You're actually very close.

    The null hypothesis (Ho) is want you want to try to "reject" (you want to try to find enough evidence to say that Ho probably isn't true, so you reject it in favor of Ha).

    Think of it in terms of the court system - "innocent until proven guilty beyond a reasonable doubt." Ho represents "innocence." Rejecting Ho in favor of Ha represents "reasonable doubt" that Ho is true.

    In your problem,

    Ho: mean response (placebo) = mean response (control)
    Ha: mean response (placebo) < mean response (control)

    I use the "<" sign because of the problem wording:
    "They hoped to find that the placebo reduced the mean response"

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