Chapter 2 Scientific Methods in Psychology. Scientific Methods in Psychology. Science is a word derived from Latin roots: Scientia meaning “knowledge”.
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Scientific practice helps psychologists to know that they have obtained the most accurate and useful knowledge of mental processes and human behavior.
Psychology is a science. This chapter is about how we utilize scientific methods in evaluating claims and theories in psychology.
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.
A good theory makes precise (falsifiable) predictions
EASILY. It is falsifiable.
NO. It is parsimonious.
It is vague.
Think – why do horoscopes never get this specific?
This is vague – What powers? How do they work?
In other words, your degree of open-mindedness should have some relationship to the quality of the evidence presented.
What information do you need to know to be a good interpreter of psychological research?
Table 2.1 definition of “assertiveness?”
Single-Blind and Double-Blind Studies
Figure 2.8 definition of “assertiveness?”
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.
Figure 2.9 definition of “assertiveness?”
In a scatterplot each dot represents data for one person; for example, each point in the center graph tells us one person’s weight and that person’s 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.
The greater the score on a depression inventory, the lower the score on a memory test
Figure 2.10 the score on a memory test
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.
Table 2.2 the score on a memory test
Comparision of Five Methods of Research
Figure 2.11 the score on a memory test
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.
Figure 2.12 the score on a memory test
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.
Not an experiment – M/F is a subject variable, not a true independent variable.
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.
Figure 2.13 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.
(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 person’s 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.
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!
Measuring and Analyzing Results
Figure 2.15 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.
Why statistics can be misleading: Both of these graphs present the same data, an increase from 20 to 22 over 1 year’s 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)
Figure 2.17 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.
The monthly salaries of the 25 employees of company X, showing the mean, median, and mode. (After Huff, 1954)
Figure 2.16 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.
Results of an imaginary survey of study habits at one college. This college apparently has two groups of students—those 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.
Calculate the mean, median and mode for this distribution of scores:
2, 3, 4, 4, 7, 10
Mean = 5
Median = 4
Mode = 4
What would be the best measure of central score for this distribution?
1, 2, 2, 3, 3, 20
What would be the best measure of central score for this distribution?
4, 4, 4, 4, 4, 4, 7, 8, 10
Figure 2.18 distribution? These two distributions of test scores have the same mean but different variances and different standard deviations.
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!
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.
Figure 2.19 distribution? 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.
FIGURE 2.20 distribution? 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.
Figure 2.21 distribution?
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.
Which is a more significant result:
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.