Assignments

Experimental Design
The design of a suitable experiment to test an hypothesis often requires some ingenuity and a suspicious nature. In modern biology, the experiment may involve very sophisticated equipment. But there are a number of features common to all good experiments (and often absent from bad ones) which exist whatever the technical details. In summary these are:
Discrimination
Experiments should be capable of discriminating clearly between different hypotheses. It often turns out that two or more hypotheses give indistinguishable results when tested by poorly-designed experiments.
Replication and generality
Living material is notoriously variable. Usually experiments must be repeated enough times for the results to be analysed statistically. Similarly, because of biological variability, we must be cautious of generalising our results either from individual creatures to others of the same species, or to other species. For instance, if our hypothesis is about mammals, it is inadequate simply to carry out our experiments on laboratory rats. Similarly, it is dangerous to extrapolate from healthy students to elite athletes.
Controls
The experiment must be well controlled. We must eliminate by proper checks the possibility that other factors in the overall test situation produce the effect we are observing, rather than the factor we are interested in.
An example: Growth hormone is secreted in response to a number of agents, including the amino acid arginine. This was shown by injecting volunteers with arginine. As a control, the investigators injected the volunteers with a saline solution. To their surprise, growth hormone was again secreted. The investigators then waved a syringe and needle in front of their volunteers, and found that that provoked growth hormone secretion too. Growth hormone is now known to be secreted in response to stress (as well as arginine).
At a more technical level, we must be sure that our method of measurement is reproducible from day to day, between operators in the same laboratory, or between laboratories. Whilst we might be confident about a balance or a ruler, can we be as sure about, say, a method for measuring haemoglobin? Do two groups of students measuring the same samples by the same methods produce the same results? Quality control helps here. 

'Blind' Designs
Investigators can subconsciously 'fudge' their data if they know what result they want to find. The answer is to do the experiment 'blind', so the investigators (and the subjects, if humans are being studied) do not know which treatment's effect they are observing. This can make the logistics of doing the experiment more complex: for example, when determining the haemoglobin concentration of male and female class members.
There is a story about a professor who devised a maze for measuring the intelligence of rats. One day he gave his technicians, who actually made the measurements, three groups of rats. He told them one group had been specially bred for intelligence, one for stupidity and the third was average. The technicians assessed the rats' intelligence and confirmed that the 'bright' group performed the best and the 'stupid' group the worst. The point is, of course, that the professor had put animals into the three groups at random. They did not differ in intelligence.
Measurement
Good experiments often, though not always, involve measuring something: a weight, say. When you make measurements, it is important you know both the accuracy and the precision of your measuring system. These two terms are not synonymous: 'accuracy' means the ability of the method to give an unbiassed answer on average, whereas 'precision' is an index of the method's reproducibility. Ideally your method should be both accurate (i.e., give the true mean) and precise (i.e., have a low standard deviation). Sometimes one is more important than the other. For example, if you were looking for small changes with time in a quantity (such as an athlete's haemoglobin concentration), you would need a precise measure of it rather more than an accurate one.
Accuracy and precision together help you to judge the reliability of your data. They also help you to judge to how many significant figures you should quote your results. For example, if you use a balance reading to the nearest gram, you should give the results to the nearest gram and not, say, to the nearest tenth of a gram. 
Some experiments are very difficult to do because it is not obvious what can be measured. This is a real problem in animal behaviour: for example, there is no obvious unit or measure for 'emotional state'. It is usually necessary to isolate measurable components of behaviour. Thus the speed at which a tiger paces up and down a cage can give some indication of the internal state of the animal but can never give a full picture of it.
Many of these points are rather abstract, but they should become clearer when you think about the following examples.

Example 1: Do plants give off water vapour?
Experiment:
Forty bean plants, growing in pots, were covered one afternoon by individual glass containers and left in the laboratory overnight. Next morning, the inside of the lid of each container was found to be covered in droplets of a fluid which proved to be water.
Conclusion:
Plants generally give off water vapour.
Critique
1. Lack of controls.
The water could have come from the plants, the soil, the pots, or the air in the jar. Control experiments should have been set up to test for these possibilities.
2. The conclusion contains some points that are not valid.
(a) The experiment was done overnight and so can tell us nothing about the behaviour of the plants at other times of day; the word 'generally' is not justified.
(b) It was carried out with an adequate number of bean plants but can tell us nothing about other kinds of plants; the word 'plants' should be qualified.
(c) There is no evidence in the experiment that water is given off as a vapour.
Example 2: Is your supermarket's 'own brand' of washing powder as good as a nationally-advertised one?
Eric Triton bemoaned the fact that his wife Ariel insisted on washing his clothes with their local supermarket's own brand of powder. He was sure the well-known brand he saw performing miracles on television most evenings would do better. He therefore set out to prove as much.
Mr Triton decided to compare the effectiveness of the two products on what his wife called 'difficult' dirt: grass stains on white linen handkerchiefs. He bought 4kg of the well-known brand for £5.17 in their supermarket and noted that the same weight of the own-brand powder would have cost £4.47. He followed the instructions on the packets exactly, weighing out the same amount of powder and using their washing machine's programme for white linens. Mr Triton was aware of the need for an index of 'cleanliness' and therefore devised a subjective scale, ranging from 10 ('whiter than white') to 0 (the starting level of dirtiness).
Mr Triton's belief was substantially confirmed. He scored the handkerchief cleaned by the national brand an impressive 8, whereas the own-brand powder only managed 7. Triumphantly, he reported the outcome to his wife. Mrs Triton, however, was unimpressed. She pointed out to her husband that there were several flaws in his experiment and convinced him that the outcome was 'not proven'.
· What do you think were the flaws that Mrs Triton could have detected?
· How should Mr Triton have done the experiment?
Further reading: Barnard C, Gilbert F and McGregor P (1993) Asking Questions in Biology, Longmans.

Unit 8 Overview 
Experimental Design
When most people think of “research,” they often think of laboratory research. In our minds, research was something that we learned about in English classes (to write papers) or in science classes. As you have learned in this course, research is a set of procedures designed to help answer a carefully constructed question or questions. In this unit, you will explore the methods used by psychologists in laboratory settings. To best understand how psychologists work in lab settings, let us take a virtual tour of a typical set of labs in a psychology department.
Imagine for a moment, a room with a table in the middle of it, computer lab stations on either side of it, a shelf of books, and a messy office in the back of the room. Does not sound like much of a laboratory, does it? Yet, this is what most labs used in the study of cognitive psychology (e.g., intelligence, memory, or perception) looks like. Most experiments are conducted with individual participants using standardized computer programs or testing equipment.
Down the hall, you might open the door to see a playroom with a box of toys and a camera mounted on the wall. This is what many child development labs look like — a place for the researcher to observe interactions, play, and testing. Sometimes, there is a two-way mirror where the researcher can observe interactions.
Further down the hall, you hear a lot of activity, as you push open the door, you see research assistants and wood mazes on separate tables. When you look further, you see that there are rats in wood mazes who are trying to swim from one side to the other. The researcher explains that this is a stress study where rats are purposely stressed (they hate water!) and then tested for cort hormone levels (e.g., similar to human cortisol or stress hormone). You want to leave now before you see how they test the brain for these levels!
This is how experiments are traditionally conducted in laboratories in psychology departments. Experimental research methods help scientists to get to the root cause of what is really going on. One of the best methods available for identifying causal relationships is the experimental method. This is because the experimental method allows the researcher to control any outside factors or additional forces that may be causing the effect. This is the only method that allows for this degree of control, and therefore it is the only method that allows for a cause and effect conclusion to be made. 
In this unit, you will describe the different experimental research designs in more detail. You will also address the important issues of both internal and external validity in experimental research, and what researchers can do to improve upon these measures. 
Click here to watch the Unit 8 Overview Video. 
A transcript for all videos is also located in Doc Sharing

Outcomes
After completing this unit, you should be able to: 
•	Describe experimental designs and control techniques
•	Evaluate the internal and external validity of experimental designs
Course outcome(s) practiced in this unit 
PS300-3: Evaluate the accuracy of conclusions derived from a research study. 

What do you have to do in this unit?
•	Complete assigned reading.
•	Participate in the Discussion.
•	Attend the Seminar.
•	Complete the Unit 8 Quiz.
•	Complete the Learning Journal.

Read the following chapter in your text:
•	Chapter 5: “Experimental” 
Prior to reading, please click on the Key Terms Icon below to review this unit’s Key Terms. This will help you to better understand the concepts as you read. There are Key Terms games to challenge yourself and also a printable PDF version. 

 PS300: Research Method I – Unit 8 Key Terms 
Control group: The group of participants in an experiment who are not exposed to the independent variable controlled during the experiment. 
Experimental group: The group of participants in an experiment who experience the researcher's independent variable (one thing changed during the experiment). 
Internal validity: The design of the experiment is such that any changes found between two groups is accounted for only the controlled independent variable. 
External validity: The extent to which the outcomes of the experiment can be generalized (used to make predictions about other similar populations) in different settings. 
Pretest: All participants in an experiment complete the test before the introduction of the controlled independent variable. 
Posttest: All participants complete the test after the experimental group has been exposed to the controlled independent variable. 
Manipulation: The process of purposely adding the independent variable into an experiment to change the experience for the experimental group.

Attending live Seminars is important to your academic success, and attendance is highly recommended. The Seminar allows you to review the important concepts presented in each unit, discuss work issues in your lives that pertain to these concepts, ask your instructor questions, and allow you to come together in real time with your fellow classmates. There will be a graded Seminar in Units 1 through 9 in this course. You must either attend the live Seminar or you must complete the Seminar alternative assignment in order to earn points for this part of the class. 
The focus of this Seminar will be on program evaluation research. 
Complete one of the following options:
Option 1: Participate in a synchronous Seminar
Option 2: Participate in an asynchronous discussion by answering the Seminar questions in written form. You should create your Seminar responses in MS Word. Your response to the questions should be composed in complete sentences and each paragraph should be at least 200–250 words in length. 
Save your answers and submit them to the Unit 8: Seminar Dropbox. Be sure to complete all questions to earn your Seminar points.
1.	Historically, experimental research in the field of psychology has suffered from a lack of external validity. Why? 
2.	What demographic group(s) have been over-represented in most of the psychological research to date? How does this influence the conclusions that have been made? 
3.	What are the key questions to ask when determining whether or not a study has external validity? How does an increase in external validity impact upon the internal validity of a study? Thoughts? 
4.	Can a balance between these two important issues be reached?

Unit 8 Quiz
You will have 1 hour to answer 15 multiple-choice questions. You will only be allowed to enter the Quiz once, so be sure that you are well prepared before doing so. There is only one correct answer for each question. You will be allowed to review your answers before submitting. If you have technical difficulties during the Quiz, contact tech support. Report the service number given to you by the technical agent to your professor. 
 
Use YouTube™, TeacherTube®, NOVA®, or Frontline websites to find videos of famous experiments conducted in psychology. 
Reflect on the following in your Learning Journal: 
1.	How did the researchers use the experimental design? 
2.	How did they protect the participants? 
3.	Also, reflect on what you would have done differently.
To begin this activity, click the Journal tab at the top of this page.