Science Investigation Surveys and Controlled Surveys (page 4)
A survey is one of the most important and widely used methods of science, even though it is seldom discussed as part of a school science class. A simple survey would be to count the number of people living in an area such as a few blocks in a small town. Less simple would be a survey that tallied and analyzed the inhabitants by age, sex, size of household, occupation, and the like. The U.S. Census attempts to do this for the entire country every 10 years. One could take a count of the different kinds of trees, birds, or other animals in an area, and that, too, would be a survey. Most people would not think of these examples as science projects. However, if these censuses or enumerations are done completely and accurately they can be called scientific as well as naturalistic observation.
For a school science investigation you may make several kinds of surveys. Let's look into an investigation of students' reaction times as a useful and interesting example of survey science. Some of you may not be clear about the differences between this kind of survey and an experiment. In an experiment, you would be trying to change something to learn what happens as a result of the change. Not so in this investigation. Here you are measuring reaction times, not trying to change them.
Measuring Reaction Times
An easy method for measuring reaction time is the "ruler-drop" method. The only materials required are an ordinary 12-inch ruler with a 3D-centimeter metric scale along one side, and, of course, the usual note-taking materials. Let's say Joe agrees to be your test subject. Seat Joe with his forearm resting on a table or desk, his hand extended over the edge, and his finger and thumb about 1 centimeter apart, ready to catch the ruler when you drop it. Hold the ruler with the zero end of the metric scale down and place it between Joe's finger and thumb but not touching either. Try to not give Joe any advance signal that you are about to drop the ruler. When you drop it, he catches it between his forefinger and thumb. You then measure on the centimeter scale how much of the ruler (how many centimeters and millimeters) passed between Joe's finger and thumb before he caught it.
You can do this as a classroom survey by pairing off the students so that each one measures the reaction time of his or her partner. You raise interest in this survey by asking them, "Do boys or girls have faster reaction times? Or is there no important difference?" Those questions may also encourage the teacher to regard your project as real science and work with you.
Demonstrate to the students how to do the ruler-drop measure, then give the partners time to practice before they do the actual measuring for their records. Each subject should plan to make five good measurements of his or her partner. Have them write down the measurements on small slips of paper or 3" x 5" index cards. The sex of the person measured should be noted but not the name. Have each person doing the measuring draw a circle around the middle value of the five measurements on the slip. This is the median (which we will discuss in more detail later in the chapter on statistics).
Collect the slips and have everyone prepare to make two lists of the median reaction times, one for boys and one for girls. You then read off from each slip the sex and the median figure for the person and have everyone note them on their lists.
When all their lists are complete, the students then figure the average, or mean, for each sex. (These calculations may also be done outside of class time.) When they are finished and can agree on the means for boys and for girls, you are then ready for them to discuss the meaning of any difference between the means. You should point out that there is sure to be some difference between the means in a complex measurement such as this one. The big question is how much difference between the means does it take to be a meaningful difference, a significant difference? In our discussion of statistics in chapter 13 we will see how scientists and statisticians deal with this question.
In this example your subjects are actively taking part in the investigation. Consequently, they may be seen as being more than just subjects under observation.
You can improve the validity of this investigation by having other students in other classrooms, preferably of the same age or grade level, make similar studies of their reaction times. In this expanded study you are almost sure to find that the average or mean reaction times of the two sexes differ among the groups. Now you can more accurately determine whether there is a real difference between the reaction times of boys and of girls.
Learn more about reaction time methods at: More Reaction-Time Methods
Like an experiment, a survey may include an independent and a dependent variable or other related variables. Consider an investigation based on this question: How much is the playing of musical instruments by children related to the playing of musical instruments by their parents? In conducting an experiment, we would have to rear children according to a prepared plan-some with parents who play musical instruments and some with parents who do not. After ten or twelve years we would compare the groups to see what we could learn.
No one, obviously, is going to do such an experiment. The only workable method is to take a survey of many parents and children. As in an experiment, the hypothesis would include a statement of two variables that the investigator suspects might be related: (1) the playing of musical instruments by parents and (2) the playing of musical instruments by their children. The hypothesis might be: "There is a statistically significant relation between the playing of musical instruments by children and the playing of musical instruments by the parents of these children."
As in an experiment, a survey may require that constants be maintained. For instance, in classifying children into two groups, those who play instruments and those who do not, we would not want to allow biases to creep into the findings. We would try to ensure, for example, that all of the children came from families of similar income level, similar educational level, and so forth. Or, to take a different approach, we would try to do a good job of randomizing the families so that all income levels, educational levels, and the like would be fairly represented in both groups of children.
Such a survey would require interviewing the children or their parents face to face, by telephone, by mail, or in some other manner, using a suitable questionnaire.
In the end, we would hope to have enough information on enough children and their parents to make a decision about the hypothesis. Would an affirmative answer ("Yes") to the hypothesis tell us that the parents' playing was a cause, or the main cause, of the children's playing? Probably not. The causes of such playing are complicated. There are many other variables that may be part of the answer. However, as a result of our survey, we may find that the two variables are related.
A Controlled Survey
A survey can also be controlled in much the same way as in a controlled experiment. The people in the survey are called the "sample" of the larger population. For example, if you survey 30 students in a classroom, out of all of the people in the world they are your "sample." In a controlled survey, you need to divide the subjects surveyed into two groups, the survey sample and the control or survey control sample. For example, if you were to investigate the effects of the hours spent watching TV have on siblings (brothers or sisters), you would create two samples, one with siblings (the survey sample) and one without siblings (the control sample). In all other respects the two groups should be as alike as possible. Give each person in the two groups a questionnaire that includes the question, "How much time do you spend watching TV per day?" When you get the questionnaires back, you can analyze them to learn if there is a significant difference between the survey group and the control group.
Survey science differs in this important way from experimental science: In doing a survey, you try not to change anything. However, you may use the results of the survey to change things. You may then need to do another survey to learn what effects, if any, the changes had.
Your undertaking of a controlled survey can be honest and scientific. It can also be an excellent basis for a display in a science fair.