Instructor: Hello students.
Welcome to Biostatistics ER, Example 4, Chapter 7.
In this example, we are going to discuss
how to determine p value
when we reject the null hypothesis.
Now, please do keep in mind
that when we do use
a statistical software package like SPSS,
the p value is generated for us,
which is an exact p value.
This is not something we can determine easily
when we are calculating the p value by hand
using the t table.
But we can have an approximate idea
where the p value will be.
So now we will learn how to do that
and we will go back to example 3,
in which we learned that our decision rule
was that we would reject the null hypothesis
if our t calculated was less than
or equal to negative 1.995
or if our t calculated was greater than
or equal to positive 1.995.
Now our t calculated here was negative 7.77,
so we could reject the null hypothesis
because negative 7.77
is less than negative 1.995.
So now the question is what is the p value?
So now we will go to the back of our textbook
and look at the degrees of freedom equal to 68,
and if we go down that row,
that has the degrees of freedom equal to 68,
we look at a two-tailed significance
with a level of 0.05,
we can see that 1.995
is the t critical value we used.
Now we need to find a number that is close
to our t calculated
and we see that that value does not exist in our table
for degrees of freedom equal to 68.
So we can state that the p value
will be less than 0.01,
which is the lowest p value we have
for a two-sided test with degrees of freedom equal to 68.
Now just to clarify,
we will go over another example.
And in this example we will assume
that the degrees of freedom is equal to 32
and our t calculated is equal to 2.12.
Now for the t critical value,
we can see for a two-sided test at alpha equal to 0.05,
the value is 2.037,
and the next t critical value
after that is 2.449.
Now our t calculated is in between
these two critical t values.
So here we can only state
that our p value is less than 0.05.
I understand that this example is a little bit different
from the previous examples
that we have covered for Chapter 7.
So if this comes across a little bit challenging,
please let me know because I'm here to help.
And again, thank you for your time and attention
and I will see you in the next video.