By Julie-Anne Spatz and Adam MacLeod Experimental Design By Julie-Anne Spatz and Adam MacLeod

Experiment vs. Observational Study An experiment deliberately imposes a treatment on a group of units or subjects in the interest of observing the response. VS. An observational study involves collecting and analyzing data without changing existing conditions or imposing a treatment.

The Experiment “This study was designed to examine the effects of carbohydrate-electrolyte ingestion on physical and mental function associated with the performance of intermittent high-intensity (IHI) exercise similar to many common competitive sporting events.” http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11932585&dopt=Abstract

In Other Words… Researchers, RS Welsh, JM Davis, JR Burke, and HG Williams, examined athletes physical performance while drinking either Gatorade or water. We will use this experiment to explain general terms about experimental design.

Units or Subjects Experimental units: the individuals on which the experiment is done Subjects: when the units are human beings The subjects used were 60 male soccer players.

Treatments Treatment: a specific experimental condition applied to the units Placebo: a dummy treatment, that can have no physical effect Factor: a controlled independent variable (called the explanatory variable), whose levels are set by the experimenter Level: each treatments specific value The factors in this experiment include the amounts of Gatorade and water given to each soccer player every fifteen minutes throughout a soccer game. Example of levels: Gatorade: 6 ounces, 8 ounces, 10 ounces Water: 6 ounces, 8 ounces, 10 ounces

Variables Control Group: the subjects that are not subjected to the treatment Experimental Group: the subjects that are subjected to the treatment Control Group: people received only water (30 people) Experimental Group: people received only Gatorade (30 people)

Randomization Randomization: the use of chance to divide experimental units into groups To conduct a completely randomized experiment: 1. use a Table of Random Digits 2. use the calculator to generate random numbers

Table of Random Digits

Calculator Technique Stat Edit highlight L1 Math PRB 5:randInt( Type in randInt(lower bound, upper bound, amount of integers needed)

Stratified Random Sampling vs. Multistage Sampling Stratified Random Sample: an experimenter would first divide the population into groups of similar individuals called a strata, then choose a separate SRS in each stratum and combine these SRSs to form the full sample Multistage Sampling: is a sample where the elements are chosen in more than one stage Ex. 1: If the experimenters wanted to do a stratified random sample, they could do this by putting soccer players in to different stratas by region of the United States and then conduct the experiment. Ex. 2: If the experimenters wanted to do a multistage sample, they could do this by choosing the soccer players at the state level, then the city level, then the county level, and then by league.

Randomization Technique Used The experimenter used a random number table to assign each soccer player a number 1 thru 60. Then, the people with odd numbers were put into the control group and the people with even numbers were put into the experimental group.

Single Blind Experiment vs. Double Blind Experiment Single Blind Experiment: the experimenters, but not the subjects know which treatment a subject received Double Blind Experiment: the experimenters nor the subjects know which treatment a subject received This experiment was a single blind experiment because the experimenter knew what groups the subjects were put in, but the subjects were not aware. To ensure that the subjects could not tell the difference between the Gatorade and water, the experimenters put a type of sweetener into the Gatorade. The sweetener only affected the flavor, but not the amount of electrolytes and carbohydrates. If the experiment were to be a double blind experiment, the experimenter would have had to of had a separate person assign which groups would receive the Gatorade and water, without the experimenters knowledge. Then the researcher could take over conducting the experiment.

Matched Pairs Matched Pairs: experiment that compares two treatments Ex. 1: If this experimenter were to use matched pairs, every soccer player would drink water throughout one game, then Gatorade throughout another, and the experimenter would note which one yielded higher performance. Ex. 2: An experiment is conducted to compare the taste of a new spaghetti sauce with the taste of a successful sauce. Each of a number of subjects tastes both sauces in random order and notes which one tastes better.

Block Design Block: a group of experimental units or subjects that are similar in ways that are expected to affect the response to the treatments Block Design: the random assignment of units to treatments is carried out separately within each block. Ex. 1: If the experimenter thought gender was an issue, the experimenter would separate the men from the women, and test the effects of both the Gatorade and the water on the two groups. Ex. 2: If the experimenter thought that age was an issue, the experimenter would separate the people into four age groups; one of people aged 1-15, one of people aged 16-30, one of people aged 31-45, and one of people aged 46-60 and test each group with the Gatorade and water. Ex. 3: If the experimenter was interested in physical condition, the experimenter would separate the subjects into two groups of strong physical condition and weak physical condition, and then test the Gatorade and water on each group.

Block Design By Gender Treatment 1 Gatorade Group 1 30 Men Treatment 2 Water Random Allocation Compare Results Treatment 1 Gatorade Group 2 30 Women Treatment 2 Water

Cautions of Experimental Design Hidden Bias: if the units or subjects are dealt with any different ways, hidden bias can arise (unequal conditions introduce bias) Ex. If the researcher were to hand a soccer player Gatorade and smile and hand the other soccer player water with a frown Lack of Realism: units or subjects may not believe in the experiment being conducted, making the results of the experiment less reliable Ex. If the soccer players already believed that Gatorade produced stronger athletic performance than water

Cautions of Experimental Design Continued Undercoverage: not including the whole population Ex. If the researcher only included soccer players from the East coast. Non-response: Some people may choose not to respond to a questionnaire or phone survey, decreasing the number of responses Ex. If some soccer players turned down the opportunity to participate in the experiment

Confounding Variables Confounding Variable: is a "hidden" variable that affects the variables in question but is not known, and distorts the resulting data In this experiment, some confounding variables include diet, athletic ability, age, weather conditions, gender, etc.

Bibliography http://helios.bto.ed.ac.uk/bto/statistics/tress2.html#DESIGN%20OF%20EXPERIMENTS http://www.stats.gla.ac.uk/steps/glossary/anova.html#treatment http://www.sytsma.com/phad530/expdesig.html http://www.stat.yale.edu/Courses/1997-98/101/expdes.htm http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11932585&dopt=Abstract