Words you will find in articles and editorials are the sensitivity of the test and the specificity of the test. The sensitivity means how effective is the test in being positive with this disease (a)/(a+c)
Think of your sensitive fingertips probing for something and finding it. The specificity means how effective is the test in being negative when people don’t have the disease (d)/(b+d)
– i.e. it is the diagonal opposite of sensitivity.