Download Research-‐Based Physiology Lecture 2: Experimental Design

Research-­‐Based Physiology Lecture 2: Experimental Design Hypothesis • Supplementary key words (eg. increase/decrease) • Measurable outcomes • Consider underlying physiological mechanisms • Eg. caffeine increases blood pressure in humans by increasing cardiac output. Manipulation hypothesis • Independent variable – thing we change (eg. caffeine) • Dependent variable – thing we are measuring • Mechanism – what is causing the change • Species (eg. human, but can be specific… obese humans or athletes) • Direction (eg. increase/decrease/not altered) Aim • Investigate, describe, characterise Approaches to investigation • Accuracy of questionnaire data • Monitoring over a period of time – when, where, how many times is reasonable? • How much drug to give and how will it be administrated? • Chronic vs acute effects – how can they be separated in time? Human vs. animal • Is it ethical to use humans – depends on design • Criteria for choosing subjects – age, health, fitness, diet, etc. • Animal subjects – are they relevant to humans? o Diet, water consumption, availability, numbers, cost, etc. Controls • Control group vs. treatment group = same except for one variable • Serial controls: same subjects used as their own control o Have one drug at one time, other at different time o Eg. caffeine and placebo – same person has alternate treatment over time • Parallel controls: different control subjects from experimental subjects (but same characteristics) o Eg. two groups of 20, one group with drug, other with placebo Number of subjects • Consider expected variability in measurements • Consider cost, time taken and feasibility in real world • 10-­‐20 subjects is usually reasonable Important issues • Time of day – changes in blood pressure and heart rate • Duration – chronic vs. accurate o For long term – days, weeks, months? § Consider cost and feasibility too • Must eliminate acute effects (eg. cannot measure directly after taking caffeine; must wait for it to clear body) • Long-­‐term experiments – can take multiple measurements to follow development of effects of caffeine