Anita
The E-15 is just a shorthand way of writing the number 0.0000000000000234.
So they are the same. A result like this can be achieved and so I 'presume'
the formula is correct.
Yes, your value is less than 0.05 and therefore is statistically significant
on the face of it.
To give more detailed answers I would have to know the nature of the inputs
to the TTEST and what hypothesis is being tested.
As an aside, the thing most likely to invalidate the interpretation of a
TTEST is not the value that the TTEST function returns, but the actual nature
of the data and the hypothesis being tested. So I wouldn't worry too much
about the TTEST result...rather I would pay closer attention to the nature of
the data being analysed...in order for a TTEST to be valid certain 'criteria'
must be met otherwise the test maybe inappropriate...
Hope this helps...
Alex
"Anita" wrote:
Yes the explanation of Ttest is very helpful thanks.
But, I still don't understand why I have an E-15 at the end of the answer.
If I change the number of decimal places to show 15 then I get a very small
number; does this therefore mean that the two means are different because the
value is significantly less than 0.05? The answer I get is something like
0.0000000000000234. Or do you think the formula is totally incorrect (I
haven't checked it at this stage)? Would you expect to get an answer like
this?
Thanks again
Anita
"Alex" wrote:
Anita
The TTEST function is a statistical test known as the t-test.
Put simply, it compares the means of two samples to assess whether they
differ significantly or not. The output is a probability value. In general a
value less than 0.05 would indicate that the two means are different.
For example, suppose you had two classes of schoolchildren, each of class
size 30. Suppose they all took the same test and received a mark out of 100.
A question may be to test whether the average (mean) mark for one class is
significantly different than the other class.
Class A ClassB
87 82
92 77
63 75
70 73
65 87
etc
In Excel you may have column A1 as class A results and column B1 as class B
results.
The mean of class A maybe 80 and the mean of class B maybe 75 ( I am making
these numbers up). So, does this suggest that the average results are
signifcantly different?
What you would do is...
TTEST([input range for classA],{input range for classB], 2,2)
And this will give a probability value e.g. 0.15. This means that the chance
of observing those results would occur about 15% by chance anyway. Typically,
a p-value of less than 0.05 (5%) is considered significant i.e. those results
would only be obtained by chance 5% of the time.
This is a very brief overview into a subject that has many nuances. This is
a light overview. If that satisfies your curiousity then fine...if not then
please do write back and I shall endeavour to explain further.
Regards
Alex
"Anita" wrote:
Hello
Can someone explain what this function does? I have to do a support call
for a customer and have never come across the Ttest function before. The
answer that I have in the cell containing the function has got E-15 after it
(which I don't understand either). I've also been asked how to calculate
probability. The version is 2000 - I can supply more detail if the above
isn't adequate.
Many thanks for your help.
Anita
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