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Manual for Experimental Reports

In psychology, as in most scientific fields, experimental reports are written in a specific format. There are two very good reasons for this. First, the format makes it easier for the reader to know where to look for information on a particular point. It is not necessary to read the entire article to find it. Secondly, the standard format makes the report easier to write. The author is spared all problems dealing with the literary structure of the report. The format specifies in which section of the report one should place particular types of information about the experiment. Thus, while writing the report, the author can focus on each section without having to make decisions about what information does or does not belong there.

Lab reports for this course will follow the standard format used in psychology. Below are the headings for the different sections that make up the experimental report given in their order of appearance. A description of what information belongs in each section follows. All sections begin with their heading entered on the page, except for the Cover sheet, the Introduction and Tables and Figures, which have no headings. The paper is double-spaced throughout.

Organization of Experimental Report

1. Cover sheet

A. Title

B. Author's name and affiliation

2. Abstract

3. Introduction

4. Method

A. Participants

B. Apparatus and materials

C. Procedure

5. Results

6. Discussion

7. References

8. Tables and Figures

1. Cover Sheet

The cover sheet includes three elements: the title, author and affiliation. It is a separate page of the manuscript with the title centered on the page, the author beneath the title, and the affiliation beneath the author.

The principal function of the title is very briefly to inform readers about the experiment. The title should be a concise statement of the main idea of the experiment, referring to the major variables or theoretical issues you have investigated. It is often a good idea to state explicitly in the title the actual variables, both dependent and independent, under investigation, for example:

"The effect of acoustic similarity on serial recall of letters"

"Display size and the span of apprehension"

Avoid words that serve no useful purpose and only increase length for examples

"A study of ..."

"An experimental investigation of ..."

The maximum length for the title is 15 words.

Your name and the name of any co-author should appear beneath the title (without the word "by"). Beneath the author's name is your institutional affiliation, i.e., Pomona College, if you are enrolled at Pomona.

Abstract

The abstract appears on the second page of the manuscript and is the only section on this page. It is typed as a single paragraph and should be between 100 and 175 words.

The abstract is a brief summary of the content and purpose of the report. It should be self contained and fully intelligible without reference to the body of the paper giving a succinct account of the main points of that section. It should include succinct information about the experimental problem, method, results and conclusions. Variables or techniques which are important in the experiment should be specifically mentioned. For example, the abstract for a study of tactile memory in blind and sighted participants would specifically mention the type of participants used.

One way to write an abstract is to write one or two sentences for each section of the report. The amount written should reflect the importance of the information for the experiment. It is probably easiest to write an abstract after you have finished the rest of the report.

3. Introduction

The introduction has no heading, but the title appears at the top of the first page of the introduction. The purpose of the introduction is to state the specific research problem under study and to explain its importance in a broader context. In other words, you should explain what you are doing in the experiment and why. The introduction should include: a brief review of previous work in the area with a clear explanation of the relationship between this work and the problem under study; a brief discussion of relevant theories and how they are related to the problem; a preview of the particular methods used in the experiment with perhaps a statement of the independent and dependent variables; finally a statement of the experimental hypothesis and the implications of the possible results of the experiment.

For example, consider an introduction for a report of an experiment investigating whether full attention is required to recognize the pitch of a target tone in noise. The introduction could open with a summary of results typically found in pitch identification. This could be followed by a description of the theoretical model of auditory recognition that has been based, in part, on these results. The problem under study would be even when the subject's attention is directed, at least in part, to another task. It would be pointed out that current theories of attention hold that there is a limitation on how much can be simultaneously attended to. There should be a summary in a few sentences of the empirical evidence for this claim focusing on studies of auditory recognition, like the present one.

Next one might describe how the problem is studied in the present experiment. The independent variable is whether or not the subject is required to perform another task, e.g., judge the duration of a light presented at the same time the target tone is presented. Another independent variable is the subject's accuracy in identifying the pitch of the tone. The hypothesis is that identification of pitch requires attention and thus, the subject's performance in identifying the tone will decline when another task is presented at the same time. In other words, it is more difficult to recognize two different stimuli at once than it is to recognize just one. It should be pointed out that in both cases, when the distracting task of judging the light is presented and when it is not, the same information is available. Thus if performance on the tone identification in the masking task is lower when the second task is presented, it suggests that full attention rather than divided attention is needed. This discussion will lead to introduction of the purpose of the present experiments, which is to test whether the two tasks interfere.

Predictions: Often an introduction section ends with prediction regarding the outcome of the experiment. Predictions are not guesses or hunches. Predictions are tests of theories. A theory makes a prediction. If the prediction is not verified by the result of the experiment, then the theory must be revised or rejected. If you have no theory, do not make "predictions."

Method

The purpose of the method is to describe exactly what was done in the experiment. The information should be specific enough that the reader could perform precisely the same experiment and thus independently verify the results. This information also allows the reader to judge whether the experiment really measures what it claims to, i.e., whether the procedure is free confounding variables, etc.

The method is usually divided into the following subsections, which begin with their headings.

Participants

This subsection gives information about who participated in the study. Participants should be described by giving their sex, age, and educational level. Other information should be included when it is relevant to the problem under study; for example, in experiments involving auditory perception it would be important to report whether participants had normal hearing, and if so, how you tested their hearing. You should always state the number of participants and how they were selected, e.g., through local schools, in dormitories, by answering an advertisement, etc. In the case of an experiment that manipulates the independent variable between participants, you should state how participants were assigned to the different groups.

Apparatus and material

This subsection describes the apparatus (e.g., equipment), and/or materials (e.g., stimuli) used in the experiment. Specialized equipment (such as a tachistoscope) obtained from a commercial establishment should be identified by the firm's name and a model number. There are experiments which use no equipment, for example a study of memory span for words in which words are presented on a card and the subject writes the response on a sheet of paper. In this case the subsection would be titled just "Materials," and would describe the words, i.e., how many syllables, parts of speech, and how they were selected.

Procedure

This subsection would summarize each step in the execution of the experiment from beginning to end. It should answer the following questions about the design of the experiment: were variables manipulated between or within participants; how were the independent variables manipulated and how many variations were there; what was the order of presentation of the variable, e.g., were the different variables presented in "blocked" or "random" order? Instructions should be summarized unless they were an independent variable and thus were used in different versions. In the latter case, the instructions should be presented verbatim. One way to organize the procedure subsection is to think about what was done to a subject from the beginning of the experiment to the end.

Note on multiple experiments: Sometimes a series of experiments are carried out to investigate a particular problem. In this case, the experiments can be reported in a single article. The overall organization of the report remains basically the same with a few changes. First, each experiment has its own section labeled with a heading, e.g., Experiment 1, Experiment 2, etc. These headings make it convenient for a reader to refer to a specific experiment. For each experimental heading the introduction, method, and results sections appear under their appropriate designation. In the introduction you should make the logic and rationale of each new experiment clear. There is usually considerable similarity among the methods for the experiments and you need not repeat information that is given in a previous experimental heading. You can simply say, "The procedure was identical to the one used in Experiment 1." A short discussion may appear under each experimental heading but it is usually combined with the results section (e.g., Results and Discussion.) A more inclusive, general discussion of all of the work should be included at the end of the report.

Results

The results section presents a summary of the data collected in the experiment. First, state the main finding of the experiment. You should be very careful to state only what the data show, not an interpretation of the data. For example, if the data from the study described above showed that there were more correct identifications of the tone when the subject did not have a distracting task, the results section could begin:

"Participants' accuracy in identifying the target tone was lower in trials when the distracting task was presented than on trials when it was not presented. The mean percent correct for all participants on trials with distraction was 65% and without distraction was 80%."

There is usually data to be presented in tables and figures. You must verbally describe in the results section any tables or figures you wish to include. However, discuss only the highlights in the text; if every item is discussed, the table becomes unnecessary. The paragraph following the one in quotes above might be:

"Table 1 presents the mean percent correct at each duration of the tone. Percent correct is shown separately for trials with distraction and without distraction. These data show that percent correct increases as the duration of the tone increases. Also, percent correct is higher for trials without distraction at most durations."

Do not present data in tables or figures when it can be presented as well in a few sentences in the text. You should refer to data concerning the effects of all independent variables, even if they are counter to your hypothesis.

If you know the proper statistical tests to perform on your data, by all means perform the tests and report the results. However, it is of no use to anyone for you to find a statistical test that you do not understand and apply it blindly in a "cookbook" fashion. Remember that the reader is interested in statistical tests only to determine that they estimate the reliability of your results. The descriptive statistics (means, percentages, scale values, etc. are what the reader wants to know, and they should be presented clearly and completely. The general rule for this class is that those who have not had a statistics course are exempted from having to perform an inferential tests of the significance of their results.

Discussion

Speculations and inferential statements are saved for this section. In the discussion, you should first evaluate your results with respect to your original hypothesis. You might also give attention to the implications of the results for the theoretical issues raised in the introduction. You should note any differences between your results and the previous research reviewed in the introduction. You should state clearly and directly what conclusions can be drawn from the study.

In addition, the discussion is the place to qualify your results and the conclusions that can be drawn from them. You can note any shortcomings of the study. It is best when discussing focus to say what difference they may make on the results. For examples, the statement that participants were not chosen randomly tells us almost nothing. It does not tell us how the results may have been influenced.

References

The reference section begins on a separate page. In it you must list all references cited in the experimental report. It is assumed you have read all references cited. The references must be listed in the references section according to a specific format, the rules of which are given below. The rules are all exemplified in the illustration that follows.

In the text. Refer to an article by citing the name of the author or authors, and put the date of the article in parentheses: "According to Author (1970) .......". If there are two authors, cite thusly: "Author and Author (1974) showed that ...". If there are three or more, name them all in the first citation, but thereafter refer to the paper by mentioning only the first author, followed by "et al." and the date if appropriate. Thus, you would say "... as found by Author, Author, and Friend (1977). The interpretation given by Author et al. is that ...". Note that in the last example the date was not repeated. It was not repeated because there was no ambiguity as to which Author et al. article was intended. The decision to repeat dates or not depends on whether or not the reference would be ambiguous without the date. There is no way to set a rule for you to follow, but when in doubt, repeat. Occasionally you will want to make a statement about a theory or result without using the author's name in the sentence. In this case the references for the statement can be put in parentheses at the end of your sentence, for example, "It has been suggested that the capacity of STM is 7 +/-2 items (Miller, 1967). If your reference is made within a parenthesis, set off the date with commas, and for multiple authors use an ampersand rather than "and". Otherwise, all the rules are the same.

In the references. For articles, the format is

Author, I., Author, J., & Author, K. (Year), Title, . Journal Name, vol. page to page.

For books the format is

Author, I., Author, J. and Author, K. (year). Title. City: Publisher.

For example:

Many studies have demonstrated that complex learning occurs in plants (e.g., Ison & Gray, 1978; Kamano, 1972). A most astounding study involving the Venus' flytrap (Dionaea muscipula) was reported by Schwartzbaum and Zimney (1982). These authors reported that "the participants were able to discriminate sugar water and vinegar injected flies with 89% accuracy" (p. 419). A follow-up study by Beatty, Gray, and Nemo (1980b) confirmed the Schwartzbaum and Zimney results. However, subsequent studies by Beatty, Gray, and Nemo (1980a) and by Ison, Doolee, and Tinker (1981) have not been able to repeat the outcomes. Ison et al. attributed the inconsistent results to the proportion of sand in the rearing soil. Many investigators have found sand content to be important only when "a fine grain analysis is made" (Bump, 1980, p. 596).

Note that when direct quotations are made in the text, you must give the page of the reference from which the quote was taken. Also note how a chapter in a book is referenced, e. g., Ison & Gray (1978).

References

Beatty, W. R., Gray, T. J., & Nemo, C. (1980). Ingestion of flies by Venus' flytraps (Dionaea muscipula): A failure to replicate. Journal of Plant Behavior, 16, 269- 275.

Beatty, W. R., Gray, T. J., & Nemo, C. (1980). Ingestion of sweet and sour flies by Venus' flytraps (Dionaea muscipula). Journal of Plant and Weed Cognition, 48, 136-137. (b)

Bump, V. R. Y. Sand, grit, and other dirt. (1980). Bulletin of the Atomic Botanist, 82, 596-604.

Ison, K. B., Doolee, F., & Tinker, B. (1981). Indiscriminate ingestion of flies by flytraps. Journal of Plant Learning and Plant Behavior, 49, 469-470.

Ison, K. B., & Gray, T. J. Forgetting in plants and elephants. In T. M., Mason & J. K. Jarr (Eds.) (1978). Learning is where you find it. New York: Mediocre Press.

Kamano, M. The neurophysiology of American plants. (1972). Outlandish, N. J: Bench Press.

Schwartzbaum, I. M. & Zimney, U. P. Task discrimination of Dionaea muscipula. (1982)

Journal of Plant Digestion, 13, 412-420.

8. Tables and figures

Tables are placed after the reference section and they are followed by figures.

A. Tables. Number all tables with Arabic numerals in the order in which they are first mentioned in text. Give every table a brief but clear explanatory title. In the title make clear that the data is, e.g., mean number of correct responses, percent errors, mean response time (in msec.), etc. When the data are statistics (e.g., means, standard deviations) it is usually sufficient to round off to two places to the right of the decimal point. But always be consistent in how many places you report for a given set of data.

B. Figures. All graphs, charts, and illustrations are called figures when mentioned in text. Number all figures consecutively with Arabic numerals. Each figure should have a caption that describes the contents of the figure in a brief sentence or phrase. In parentheses after the figure caption, add any information needed for clarification, such as an explanation of units of measurement. Also be sure to label the axes of the figures and the separate lines or curves in the figure.