sensitivity and specificty again

[Gamewizard]

Hi,

 

A total of 4543 patients were tested. A total of 300 patients had cancer. A total of 250 patients tested positive for cancer, of which 84% had cancer.

 

I need to work out the true positives, false postives, true negatives and false negatives. How would I go about finding this out from this type of data.

 

please help

[Mr Skeptic]

Divide up everyone into the four groups, and exchange all your percentages with numbers.

[Gamewizard]

But i dont understand. There is only 84%, there are no other percentages

[CharonY]

You have several values. Those that have cancer, those that don't, those that were tested positive, and those that were not. Draw a table with the FP, TP, FN an TN and try to assign the values.

 

Tip 1: you can calculate percentages out of those numbers.

Tip 2: If a population consists of two groups and the percentage belonging to one is 84%, what is the percentage of the other (remaining group)?

[rmw]

Think logically and carefully.

 

All the patients were tested, but only 250 had positive tests.

 

But 300 altogether had cancer. that means 300 - 250 had cancer, but tested negative. False negatives 50

 

Now, of the 250 that tested positive, only 84% (210) actually had cancer. that means 40 tested positive but did not have it. False positives 40

 

The 210 who tested positive and actually had cancer are the true positives. True positives 210

 

So, 4543 - 300 (4253) did not have cancer. But, of these, 40 had false positive tests. That leaves 4253 - 40 as true negatives. True negatives 4213.

 

On the other hand, I know absolutely nothing about this so I could be wrong.

 

 

[Gamewizard]

Thanks for all your replies I know how to work it out now.