Creating a function that preforms two sample t-tests with unequal variances

Hello -- I am pretty new at Matlab, I am currently towards the end of a one-semeter course. For this reason please don't use fancy technical jargon in your answers becuase I'm going to have no idea what you're saying.

My main problem is, is that I don't how how to assign vartype. I have on a second page all of the defined values for the things like MX and pooled variance. I have googled for literally hours on how to assign vartype and it seems that everyone has a different process, and none of them are working for my function. It seems a lot of people like strings:

function [tStat, df, pvalue] = newttest(X,Y,vartype)

%this function performs pooled and unpooled t-tests

%this function uses unpaired two sample t-tests

if vartype==1

%Performing a pooled variance t-test

%if the distributions are equal then compute pooled variance t-test

tStat = (MX/MY)/(sqrt(pooledvariance)/(1/n1+1/n2))

df = n1+n2-2

pValue = 2 * tcdf(-abs(tStat), df);

else vartype==2

%Performing an unpooled variance t-test

%if distributions are unequal then compute unpooled variance t-test

tStat = (MX/MY)/sqrt((Xvar/n1)+(Yvar/n2))

df = ((Xvar/n1+Yvar/n2)^2)/((Xvar/n1)^2)*(1/(n1-1))+((Yvar/n2)^2)*(1/(n2-1))

pValue = 2 * tcdf(-abs(tStat), df);

end

^here is my function. I built the function from a skeleton that my professor provided.

When I run this code, I recieve:

>> newttest

Not enough input arguments.

Error in newttest (line 5)

if vartype==1

I'm sure there's a simple solution to this but I have no idea what it is.

Answer 1

[Star Strider]

‘My main problem is, is that I don't how how to assign vartype.’

I’m not certain what you’re asking. It appears that ‘vartype’ is either 1 or 2, depending on the test you want to do.

.

[Monica Joan Zielinski]

correct - 1 means they're of equal variance and 2 means they're unequal, in this case.

I thought my function wasn't running because I didn't assign vartype correctly, but is this not the case? As in, I figured the error 'not enough input arguments' was referencing how I assigned vartype. Am I doing someting else wrong?

[Monica Joan Zielinski]

When I spoke to my professor about this he said

"You need to pass X and Y as inputs to your newttest function. So you need to call it for example, newttest(X,Y,1)"

I'm not sure what is mean to pass X and Y as inputs?

[Star Strider]

‘Am I doing someting else wrong?’

Yes, sort of.

Several variables are not defined: ‘pooledvariance’, ‘Xvar’ and ‘Yvar’. The funciton will not automatically assign the data inputs to ‘Xvar’ and ‘Yvar’. They need to be assigned specifically. The ‘pooledvariance’ variable is completely missing, at least in the code you posted.

‘I'm not sure what is mean to pass X and Y as inputs?’

The inputs are the function arguments: ‘X’, ‘Y’, and ‘vartype’. The first two need to be vectors, and the last one is a scalar.

.