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1 Chapter 2Scientific Methods in Psychology 2 Scientific Methods in Psychology
Science is a word derived from Latin roots
Scientia meaning knowledge
Scientific practice helps psychologists to know that they have obtained the most accurate and useful knowledge of mental processes and human behavior. 3 Module 2.1
Science and the Evaluation of Evidence
4 Science and the Evaluation of Evidence
Psychology is a science. This chapter is about how we utilize scientific methods in evaluating claims and theories in psychology.
5 The Scientific Method
Why do we need it
The scientific method provides guidelines for scientists in all fields including psychology to use in evaluating discrete claims (called hypotheses) and broader theories.
6 The Scientific Method
Why do we need it
It is almost impossible to prove with utter certainty that any individual claim or theory is true beyond a doubt.
The scientific method allows us to declare our conclusions to be probable to the point where it is reasonable to treat them as factual.
7 The Scientific Method
How do we support claims scientifically
Scientists want to know the evidence that will support or disprove a claim.
The scientific word for a claim is hypothesis.
A hypothesis is a testable prediction of what will occur under a stated set of conditions.
8 The Scientific Method
Whats the hypothesis
Claim There Is a relationship between televised violence and aggressive behavior.
9
Figure 2.1
A hypothesis leads to predictions. An experimental method tests those predictions a confirmation of a prediction supports the hypothesis a disconfirmation indicates a need to revise or discard the hypothesis. Conclusions remain tentative especially after only one experiment. Most scientists avoid saying that their results prove a conclusion.
10 The Scientific Method
How do we test the hypothesis
Some possible methods
Measure how much time a sample of children watch violent television programs and compare that to how much violent behavior the children exhibit (a correlational study.)
Have a group of children watch violent programs and another group watch non-violent programs and then record the differences in amount of violent behavior between the two groups (an experimental study.)
11 The Scientific Method
How do we measure the results
It is tricky to measure phenomena such as violent behavior.
We need to operationally define concepts such as this one clearly stating which behaviors will represent the phenomenon of interest (verbal threats hitting etc.).
We need to apply the definitions consistently.
12 The Scientific Method
What do our results mean
If the results support the original prediction it may mean the hypothesis is valid but that does not eliminate other possible explanations for the outcome.
If the results contradict the original prediction the hypothesis may need to be modified or abandoned (at least under certain circumstances.)
Scientists generally do not make any dramatic alterations to their conclusions based on one study only.
13 The Scientific Method
The importance of replication
The standards in the scientific community demand that researchers report their methods in enough detail so that any other scientist could feasibly repeat the study to confirm or contradict the validity of the findings.
Replicable results are those that anyone can obtain at least approximately by following the same procedures.
14 The Scientific Method
A good example of an interesting non-replicable result in psychology is the much-ballyhooed Mozart effect.
Based the results of a single study researchers claimed that listening to classical music could improve cognitive functioning.
Several other studies have failed to replicate the results of the original one.
15 The Scientific Method
The method of meta-analysis
Because we sometimes find predominance of small to medium effects in most studies of a particular phenomenon (such as sex differences in aggressive behavior) we may compile the results of a large number of studies and treat them for all intents and purposes as one very large research study.
A meta-analysis also provides us with more information about the circumstances that will increase or decrease the likelihood of the predicted effect occurring.
16 Scientific Theories
What is a theory
A theory is a comprehensive explanation of observable events and conditions.
A good theory makes precise and consistent predictions while relying on a small number of underlying assumptions.
17
Figure 2.2
A good theory makes precise (falsifiable) predictions
18 Scientific Theories
The importance of falsifiability and parsimony
A theory that makes precise predictions is falsifiable because it is easy to think of evidence that would confirm or contradict the theory.
Reliance on the fewest and simplest possible assumptions is called parsimony and is considered an essential strength of good scientific theory.
19 Scientific Theories
Example of a Parsimonious and Falsifiable Scientific Theory
Gravity is a force that pulls objects in the universe towards each other.
According to the theory of gravity larger and more massive objects pull smaller objects towards them.
20
Can you think of examples of evidence that would confirm or contradict this theory
Does the theory rely on assumptions other than the existence of the force itself and the effects of size on the workings of the force
EASILY. It is falsifiable. NO. It is parsimonious. 21
An example of a claim that is NOT falsifiable
The telephone psychic says Next year you will go through a big change.
This is not falsifiable because it is too vague.
22
An example of a claim that is NOT parsimonious
The sun goes around the earth. Little gnomes push it around the sky every day. We cant see them because they are invisible to the human eye.
This is not parsimonious because too many assumptions must be made in order for the claim to be accepted as fact.
23 Concept Check
Is this claim falsifiable
You will encounter new challenges in your travels this week.
NO It is vague. 24
An oversupply of dopamine in the human central nervous system will eventually result in a decline in the number of receptors available for that neurotransmitter.
YES 25
On March 19th 2005 you will meet a 30-year-old millionaire who will offer you an exciting entry-level job in a growing high-tech company in Austin TX.
YES Think why do horoscopes never get this specific 26
Children whose parents divorce will eventually have serious emotional and relationship problems.
NOT AS SUCH We need to operationalize the terms emotional problems and relationship problems. 27
There are unseen powers at work in our lives that scientists will never be able to fully explain.
NO This is vague What powers How do they work 28 Parsimony and Degrees of Open-mindedness
You might ask -
Shouldnt we remain open-minded to new possibilities
29 Scientific open-mindedness
It is the willingness to consider proper evidence.
It is NOT unquestioning acceptance of any possibility in the absence of evidence. This is known as gullibility.
In other words your degree of open-mindedness should have some relationship to the quality of the evidence presented. 30 What about anecdotal evidence
People often use personal accounts of isolated events to bolster their beliefs in phenomena (such as ESP.)
Because this sort of evidence is not systematically gathered it is prone to selective memory (called confirmation bias) on the part of the reporter.
We tend to remember when our hunches come true and forget when they do not. We like to be right.
31 Research on ESP (Extrasensory Perception)
Because of the problems described above anecdotal evidence is not considered to be acceptable as good evidence of the existence of ESP.
Experiments done in controlled settings such as the Ganzfeld procedure along with careful observation of some famous professional psychics have shown results that were non-replicable or easily explainable by techniques of slight-of-hand known well to experienced magicians.
32 Psychology as a Science
Science does not deal with proof or certainty.
The history of science is one of constant revision in the face of new and compelling evidence.
Yet in psychology and all other sciences we apply the rigorous and systematic methods of scientific study hypothesis methods results and interpretation to ensure that our claims are firmly grounded and our revisions reflect an improved understanding of the phenomena under scrutiny.
33 Module 2.2
Conducting Psychological Research
34 General Principles of Research
It is essential to your learning in psychology and perhaps to your knowledge in general to be able to evaluate the quality of the evidence presented in psychological research.
What information do you need to know to be a good interpreter of psychological research 35 General Principles of Research
Definitions of Psychological Terms
The Problems of Measurement
We need to measure the phenomena we are studying.
Sometimes what we study in psychology is not tangible. It is not as we are measuring weight or length of time.
36 General Principles of Research
Definitions of Psychological Terms
The problems of Measurements
In order to accurately measure these concepts and phenomena we develop behavioral or observable definitions of them.
We call these definitions operational definitions.
An operational definition is one that specifies the operations or procedures used to produce or measure something. Its a way to give an intangible idea a numerical value.
37 General Principles of Research
Definitions of Psychological Terms
So if we are investigating the effect of watching violence on television on childrens aggressive behavior
We need to operationalize violence on television.
We need to operationalize aggressive behavior.
38 General Principles of Research
Definitions of Psychological Terms
Violence might be operationalized as the number of times in a one-hour show that one person threatens or injures another person.
Aggressive behavior might be operationalized as the number of insults threats and assaults by the subject over a 24-hour period after watching a particular television program.
(There are other versions of these operational definitions that would work well.) 39 Concept Check
Operational definitions
Which of the following might be used as an operational definition of attraction
A feeling of affection when two people are together. (1)
The number of minutes during which two people are touching each other over a four-hour period. (2)
(2)
40
Which of the following might be used as an operational definition of assertiveness
The number of times a person makes requests or states his or her feelings over the course of a one-hour interaction. (1)
An appearance of confidence and ease in social situations. (2)
(1)
41 General Principles of Research
Population Samples
Usually in research we are asking questions that are pertinent to a large population of interest such as
Seven to ten-year-old children
People diagnosed with depression
42 General Principles of Research
Population Samples
But it is not practical to study all the individuals in the population.
We take a relatively small number of observations or individuals from the population and we generalize from that small number.
The small number of individuals or observations is called a sample.
43 General Principles of Research
Population Samples
There are several types of samples and sampling procedures
A convenience sample is a group chosen because of its ease of availability and study.
A representative sample closely resembles the population in its percentage of males and females ethnic or racial groups age levels or whatever other characteristics might have some relevance to the results.
44 General Principles of Research
Population Samples
A random sample is one in which every individual in the population has an equal chance of being selected.
A cross-cultural sample is one that contains groups of people from at least two distinct cultures.
45 General Principles of Research
Population Samples
How we go about obtaining a sample has to be carefully assessed in terms of our resources and goals. Sometimes it is acceptable and appropriate to rely on a convenience sample other times this strategy will produce results that are useless in helping us understand and interpret the real world.
46 Concept Check
Population Samples
Suppose I am interested in the attitudes of college students towards using the Internet in their studies. I survey my students in one Introductory Psychology class at my college.
Can I assume that their attitudes are representative of the attitudes of all college students in general
Population Samples
Suppose I am interested in the attitudes of college students towards using the Internet in their studies. I survey my students in one Introductory Psychology class at my college.
Not a safe assumption why 47 General Principles of Research
Experimenter Bias
Because (fallible) humans do the research we need to keep in check the various tendencies that can work to create erroneous research findings or erroneous interpretations of findings.
Experimenter bias is the tendency of an experimenter to unintentionally distort the procedures or results of an experiment based on the expected or desired outcome of the research.
48 General Principles of Research
Experimenter Bias
For example if you were a researcher testing the hypothesis that children who have been diagnosed with learning disabilities are on average more creative than children who have no diagnosis you may find it hard to ignore your hypothesis as you observe the children with an LD diagnosis going about whatever tasks you have devised to operationalize creativity.
49 General Principles of Research
Experimenter Bias
Methods have been devised to help counteract these normal human tendencies that create bias
Using blind observers who record data without knowing what the researcher is studying.
Using a placebo control. A placebo is a pill or other sham treatment that makes it very difficult for the subjects (single-blind) or the subjects and experimenter (double-blind) to know who has received the treatment and who has not.
50
Table 2.1
Single-Blind and Double-Blind Studies
51 General Principles of Research
Research design
There are many methods used to study psychological concepts and phenomena.
We start by asking ourselves what happens and under what circumstances does it seem to occur
We try to choose the best procedure. Each method has advantages and disadvantages.
52 General Principles of Research
Observational (non-experimental) Research Design
Naturalistic Observation
Careful monitoring and examination of what people and animals do under more or less natural circumstances.
Example Dr. Jane Goodalls decades-long observation of chimpanzees in the forest of Gombe recording their social organization and biological functioning.
53 General Principles of Research
Observational Research Design
Case History
A thorough observation and description of a single individual appropriate only when done for an unusual condition or circumstance.
Example The case of Phineas Gage whose bizarre and unfortunate accident taught medical doctors and psychologists much about the nature of the prefrontal cortex of the brain.
54 General Principles of Research
Observational Research Design
Survey
A survey is a study of the prevalence of certain beliefs attitudes or behaviors based on peoples responses to specific questions.
Example Albert Kinseys 1948 survey of the sexual preferences and habits of Americans was ground breaking although not by any means beyond criticism.
55 General Principles of Research
Observational Research Design
Surveys
A Few Concerns About Survey Research
Problems with obtaining a random or representative sample
Competence or honesty of those who respond
The wording of the questions
Surveyor bias
56
Figure 2.8
An example of how to bias a survey. This imaginary survey for an imaginary society has a style of questions similar to those found in many surveys sponsored by actual political and social organizations. The request for a donation is a reliable clue that the organization is not really seeking your opinion and will probably not even bother to tabulate the results.
57 General Principles of Research
Correlational Studies
Correlation
Correlation is a measure of the relationship between two variables which are both outside of the investigators control.
Examples of variables include aspects such as height weight socio-economic level number of years of education.
The mathematical estimate of the strength and direction of a correlation is the correlation coefficient.
58 General Principles of Research
Correlational Studies
The value of the correlation coefficient can range from 1.00 to 1.00.
The higher the absolute value the stronger the relationship is regardless of the direction.
A negative correlation (-) means that as one variable increases the other decreases. An example of a negative correlation is the more absences a student has the lower his or her grade in psychology is (more absences accompanied by fewer points on tests.)
59
Figure 2.9
In a scatterplot each dot represents data for one person for example each point in the center graph tells us one persons weight and that persons grade on the psychology final exam in this case using hypothetical data. A positive correlation indicates that as one variable increases the other generally does also. A negative correlation indicates that as one variable increases the other generally decreases. The closer a correlation coefficient is to 11 or 21 the stronger the relationship.
60 General Principles of Research
Correlational Studies
A positive correlation () means that as one variable increases so does the other. An example of a positive correlation would be the higher the annual income the greater the amount and number of donations to charity (more income accompanied by more charitable giving.)
A zero or near zero correlation means that the variables have no relationship that changes in one are not related to any type of change in the other.
61 Concept Check
What type of correlation
Peoples shoe size and IQ score
Zero
62
The greater the number of years of education the higher the income
Positive 63
The greater the score on a depression inventory the lower the score on a memory test
Negative 64
Which relationship is stronger
. 30 or -.90
-.90
65 General Principles of Research
Correlational Studies
Some Problems with Interpreting Correlational Research
Illusory Correlation An apparent relationship based on casual observations of unrelated or weakly related events.
Example The belief in moon madness.
66 General Principles of Research
Correlational Studies
Some Problems with Interpreting Correlational Research
Correlation Causation Correlational research only tells us if two variables are related and how strongly. It does not tell us why two conditions can appear together and yet not cause each other.
Example The more someone weighs the larger his or her vocabulary is. Do you know why
Because weight and vocabulary both increase with age. 67
Figure 2.10
A strong correlation between depression and impaired sleep does not tell us whether depression interferes with sleep poor sleep leads to depression or whether another problem leads to both depression and sleep problems.
68 Concept Check
Interpreting correlational research
Suppose we did a research study on our campus and found a -.75 correlation between frequency of exercise and level of depression.
List all the possible conclusions that we might draw from this study.
Exercising makes depression less likely.
Depression makes exercising less likely.
A third variable causes increases in exercise and decreases
in depression.
69
Table 2.2
Comparision of Five Methods of Research
70 General Principles of Research
Experiments
Experiment
A study in which the investigator manipulates at least one variable (independent) while measuring at least one other variable (dependent).
71
Figure 2.11
An experimenter manipulates the independent variable (in this case the programs people watch) so that two or more groups experience different treatments. Then the experimenter measures the dependent variable (in this case pulse rate) to see how the independent variable affected it.
72 General Principles of Research
Experiments
Example To test whether the hormone adrenaline enhances memory in mammals a researcher teaches rats to run a maze. She gives a randomly selected portion of the rats a drug to block production of adrenaline. She then times all the rats on the maze.
73 General Principles of Research
Experiments
Remember In order for a study to be a true EXPERIMENT one of the variables must be directly under the researchers control and the other must be measurable in some scientific way.
74
Figure 2.12
Once researchers decide on the hypothesis they want to test they must design the experiment. These procedures test the effects of watching televised violence. An appropriate accurate method of measurement is essential.
75 Concept Check
Is it an experiment If so name the independent and dependent variables.
A researcher wants to know if men or women are better at a particular set of spatial relationship tasks. He compares a randomly selected group of 50 men and 50 women on a test of the task.
Not an experiment M/F is a subject variable not a true independent variable. 76
A researcher wants to know if a particular herbal supplement is helpful for improving memory. She selects 100 college sophomores who achieved an average score on a memory test gives half of them the herb for one month half of them an inert pill and the re-tests them all.
Yes IV herb/no herb DV score on memory test 77 General Principles of Research
Experiments
Other important terminology
Experimental group The set of individuals who receive the treatment that the experiment is designed to test.
Control group The set of individuals who are treated in the same way as the experimental group except for the procedure that the experiment is designed to test.
Random assignment A selection method in which the experimenter assigns subjects to either the experimental or control group using a procedure based on chance.
78 General Principles of Research
Experiments
Possible problems in carrying out and interpreting the results of experiments
Demand Characteristics Cues that tell a subject what is expected of him or her and what the researcher hopes to find.
Example If the subject knows that the drug being tested is supposed to improve mood he or she may feel better.
79
Figure 2.13
(a) In experiments on sensory deprivation a person who is deprived of most sensory stimulation becomes disoriented loses track of time and reports hallucinations. But do these results partly reflect the persons expectation of having distorted experiences (b) In one experiment students were placed in a normal room after undergoing various procedures designed to make them expect a dreadful experience. Many reported hallucinations and distress.
80 General Principles of Research
Experiments
Possible problems in carrying out and interpreting the results of experiments
Ethical Considerations In doing research with humans or animals researchers must way possible harm that may be inflicted against the usefulness and other benefits that may be gained.
81 General Principles of Research
Ethical Concerns in Research involving Human Subjects
Safeguarding human subjects well-being
Use of informed consent Subjects are advised on what to expect and explicitly state that they agree to continue.
Institutional Research Board (IRB) Approval A university or other reputable institution appoints a panel of qualified judges who review all research proposals before the actual experiment begins.
82 General Principles of Research
Ethical Concerns in Research involving Human Subjects
American Psychological Association standards The criteria for appropriate treatment of humans who are experimental subjects are well known to members of this largest professional organization in the science. Censure and expulsion are possible consequences for those who do not follow these procedures.
83 General Principles of Research
Ethical Concerns in Research involving Animals
Though highly controversial research studies that use animals to help us understand the body and brain have been essential to progress in medicine and psychology.
Criteria for care and use of animals are established by professional organizations
APA
The Neuroscience Society
Animal care committees at research institutions
84 General Principles of Research
Ethical Concerns in Research involving Animals
Following the guidelines animal care committees strive to
Ensure that research animals are treated humanely
Ensure that any pain and discomfort are kept to a minimum
Ensure that all alternatives are examined before animals are subjected to potentially painful procedures
Nonetheless this area continues to be one of great debate and no compromise between the sides ever seems 100 satisfactory.
85 Psychological Research
Because of the challenges involved in studying intangible mental processes and human behavior that is the product of diverse influences psychologists have developed procedures that are rigorous and inventive and very frequently do increase our understanding of the phenomena in this complex and fascinating science!
86 Module 2.3
Measuring and Analyzing Results
87
Figure 2.15
Why statistics can be misleading Both of these graphs present the same data an increase from 20 to 22 over 1 years time. But by ranging only from 20 to 22 (rather than from 0 to 22) graph (b) makes that increase look much more dramatic. (After Huff 1954)
88 Descriptive Statistics
Descriptive statistics are mathematical summaries of results. There are two broad categories of descriptive statistics
Measurements of the Central Score
Measurements of Variation or Dispersion
89 Descriptive Statistics
Measurements of the Central Score The mean
The mean is the sum of all the scores divided by the total number of scores. This measure is most useful when the scores are normally distributed.
A normal distribution or normal curve is a symmetrical frequency of scores clustered around the mean.
90 Descriptive Statistics
Measurements of the Central Score The median
The median is the middle score when we arrange all the scores in order from lowest to highest.
It is especially useful when the scores we are working with are very abnormally distributed.
For example if our distribution of scores is 2 3 and 10 3 is a more accurate description of the middle then the mean which would be 5 for this set of scores.
91
Figure 2.17
The monthly salaries of the 25 employees of company X showing the mean median and mode. (After Huff 1954)
92 Descriptive Statistics
Measurements of the Central Score The mode
The mode is the score that occurs most frequently in a distribution.
The least useful of the three measures of central score it comes in handy when a distribution is very abnormally distributed (when the majority of scores are clustered at the low end or high end) or when working with non-numerical data (categorical variables such as diagnostic classifications.)
93
Figure 2.16
Results of an imaginary survey of study habits at one college. This college apparently has two groups of studentsthose who study as hard as they can and those who find other things to do. In this case both the mean and the median are misleading. This distribution is bimodal its two modes are 0 and 8.
94 Concept Check
Calculate the mean median and mode for this distribution of scores
2 3 4 4 7 10
Mean 5 Median 4 Mode 4 95
What would be the best measure of central score for this distribution
1 2 2 3 3 20
Median 96
What would be the best measure of central score for this distribution
4 4 4 4 4 4 7 8 10
Mode 97 Descriptive Statistics
Measurements of Variation
The range is a statement of the highest and lowest scores
If our distribution has the following scores 1 2 3 5 7 9 9 10 the range is from 1 to 10.
98 Descriptive Statistics
Measurements of Variation
The standard deviation (SD) is a measurement of the amount of variation among scores in a normal distribution.
The more closely the scores are clustered around the mean the smaller the standard deviation is.
Standard deviations are used to make meaningful comparisons on different tests or on different versions of the same kind of test.
99
Figure 2.18 These two distributions of test scores have the same mean but different variances and different standard deviations.
100 Concept Check
On your first statistics exam of the semester you get a score of 90 the mean for the class is 70 and the standard deviation is 20. On the second exam of the semester you get an 80. The mean for the class is 65 and the standard deviation is 5. Did you do better worse or the same on the second test
You did much much better on exam 2! 101 Evaluating Results Inferential Statistics
As mentioned earlier in the module we rarely are certain in the world of research. To infer is to guess based on evidence. Inferential statistics are the mathematical procedures we use for this educated guessing a statement about a large population based on an inference from a small sample.
102
Figure 2.19 In a normal distribution of scores the amount of variation from the mean can be measured in standard deviations. In this example scores between 400 and 600 are said to be within 1 standard deviation from the mean scores between 300 and 700 are within 2 standard deviations.
103 Evaluating Results Inferential Statistics
Sometimes we try to infer where the true mean of the population of interest is based on the mean of our sample.
We use a confidence interval to state how sure we are that the true mean lies within a certain range.
The calculation of width of the confidence interval is based on the size of the sample (the larger the better) and the value of the standard deviation (the smaller the better.)
Example Based on my analysis of this sample I am 95 certain that the true population mean lies between 5.0 and 7.0.
104 Evaluating Results Inferential Statistics
Confidence Intervals
Confidence intervals are typically reported at the 90 95 or 99 levels of certainty.
The higher the confidence level the broader the range that is given by the researcher.
If the standard deviation is small and the sample on which the confidence interval is based is large we can increase our certainty without necessarily broadening the range.
105
FIGURE 2.20 The vertical lines indicate 95 confidence intervals. The pair of graphs in part a indicate that the true mean has a 95 chance of falling within a very narrow range. The graphs in b indicate a wider range and therefore suggest less certainty that reward is a more effective therapy than punishment.
106 Evaluating Results Inferential Statistics
Probability Values
A probability value is a way to estimate if a score would be extremely rare given what we know about the likely range in which the population mean falls.
If the researcher says that there is a 95 certainty that the population mean falls between 5.0 and 7.0 and a particular score falls at 8.2 then that score has a probability value of less than 5 (p in some way.
107 Evaluating Results Inferential Statistics
Probability Values and Statistical Significance
Often scores that are exceptional in this way are interpreted as being unlikely to have arisen by chance.
A result that is unlikely to have occurred by chance in a distribution is interpreted as being statistically reliable or statistically significant.
108
Figure 2.21
Researchers say that results are statistically significant if they calculate that chance variations in data would be unlikely to produce a difference between groups as large as the one that the researchers actually observed.
109 Concept Check
Which is a more significant result
One that is obtained with a p-value of .10 OR
One obtained with a p-value of .001
.001 110 Statistics and Conclusions
Consistent dependable large effects do not require statistics for analysis and interpretation. They speak for themselves.
Psychologists are often dealing with small and fragile effects or effects that only arise under a certain set of circumstances. To do meaningful work in this science we need a solid understanding of research design and statistics.
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