Differentiate between a sample and population. Identify strategies to reduce participant attrition. Differentiate between random sampling and random allocation to groups. Develop strategies to strengthen reliability of measurements. Define validity. Identify means to evaluate the validity of psychometric instruments. Assess the validity and reliability of selected instruments. Compare and contrast measurement tools for selected concepts. Describe strategies to ensure the accuracy of physiologic measures. Assess precision of physiological measures in selected studies Assess the elements of a data collection plan