Differentiating specific problem areas is the function of diagnostic testing. For example, if someone has difficulty concentrating, the source of the problem may be anxiety, depression or other mood disturbances, or a biologically determined cognitive problem like ADHD or LD. Administration of cognitive tests ( like the WISC-IV or WIAT-II [a basic intelligence test and skills achievement test, respectively]) and projective tests, (like The Rorschach Inkblot Test and the Thematic Apperception Test) helps clarify the source of the problem and is effective in developing and guiding a treatment plan