On 5/25/2011 8:35 PM, lubna alidrus wrote:
> A dermatologist tested a new topical application for the treatment
> of psoriasis on 47 patients. He applied it to the lesions on one part
> of the patient's body and what he considered to be the best
> traditional remedy to the lesions on another but comparable part of
> the body, the choice of area being made by the toss of a coin. In
> three patients both areas of psoriasis responded; in 28 patients the
> disease responded to the traditional remedy but hardly or not at all
> to the new one; in 13 it responded to the new one but hardly or not
> at all to the traditional remedy; and in four cases neither remedy
> caused an appreciable response.
This is a special case because the data is paired. Each subject gets
both the new treatment and the best traditional remedy.
The Z test you propose works for independent data, but not matched data.
Do a Google search on McNemar's test and see if you can apply it to this
data.
If you can't figure this out after reading what's on the web, send me a
private email and I'll elaborate in more detail.
Steve Simon, [log in to unmask], Standard Disclaimer.
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> A)Tabulate this data.
>
> B)Calculate the summary statistic that would compare the two
> treatments.
>
> C)What would be the appropriate test of significance to compare the
> two treatments? Give reasons
>
> D)Did either remedy cause a significantly better response than the
> other? Explain. (Z= 2.2 p=0.028)
>
> *Answer:*
>
> *A)*
>
> *Member of pair receiving treatment A(trad)*
>
>
>
> *Member of pair receiving treatment B(topical)*
>
>
>
> *Pairs of patients*
>
> Responded
>
>
>
> Responded
>
>
>
> 3
>
> Responded
>
>
>
> Did not respond
>
>
>
> 28
>
> Did not respond
>
>
>
> Responded
>
>
>
> 13
>
> Did not respond
>
>
>
> Did not respond
>
>
>
> 4
>
> Total
>
>
>
>
>
> 48
>
> B) Percentage of patients who responded to traditional remedy only
>
> 28/48x100= 58.3%
>
> Percentage of patients who responded to topical treatment only
>
> 13/48x100 = 27.08%
>
> Percentage of patients who responded to traditional + topical = 3
>
> 3/48x100= 6.25%
>
> Percentage of patients who did not responded to either topical or
> traditional = 4
>
> 4/48x100=8.3%
>
> Therefore of the two treatments, the traditional remedy (58.3%) had a
> better response towards psoriasis than the new topical treatment
> (27.08%)
>
> C) Z test should be done as the population is more than 30
>
> D)The z value is 2.2 which is more than 1.96, thus we should reject
> the null hypothesis. The p value here is 0.028 which is less than
> 0.05
>
> ( P<0.05)Therefore it shows a highly significant difference. Thus the
> traditional remedy showed a significantly better response.
>
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