Research Assignment #23: Design experimental design & and explore the different purposes or roles of Variables For the Departments of English & Media Studies by Prof Dr Sohail Ansari

                                              

Experimental design

 Instructor: Devin Kowalczyk

Devin has taught psychology and has a master's degree in clinical forensic psychology. He is working on his PhD.

This lesson explores the terminology of experimental design. What are variables? How do they influence each other? Is it possible that you are seeing connections that don't actually exist?

Research

As a researcher, you're going to perform an experiment. I'm kind of hungry right now, so let's say your experiment will examine four people's ability to throw a ball when they haven't eaten for a specific period of time - 6, 12, 18 and 24 hours.

Task: As a researcher, you're going to perform an experiment. People you assume on the basis of an essay of research assignment 20 are not happy with the king or his way of governance, so let's say your experiment will examine ….. People’s …… to ……..

(Complete a sentence)

We can say that in your experiment, you are going to do something and then see what happens to other things. But, that sentence isn't very scientific. So, we're going to learn some new words to replace the unscientific ones, so we can provide a scientific explanation for what you're going to do in your experiment.

The starting point here is to identify what a variable is. A variable is defined as anything that has a quantity or quality that varies. Your experiment's variables are not eating and throwing a ball.

Task: You examine people from different walks of life

You examine people belonging to different age groups

You examine people having different litracy levels.

Your variable is defined as……

Let's say your experiment will examine people's ability to judge a king.

Questions:

Do you think this experiment will serve our purpose?

Do you thinl for this experiment we need people from different walks of life? Different age groups?  Different litrarcy levels?

If you think this experiment will not serve our purpose so devise other experiemtent.

Do not you think we need to examine people from different professions, age groups and having different litracy levels as all these have the impact on the way people perceive?   

‘Now, let's science up that earlier statement. 'You are going to manipulate a variable to see what happens to another variable.' It still isn't quite right because we're using the blandest term for variable, and we didn't differentiate between the variables. Let's take a look at some other terms that will help us make this statement more scientific and specific.

Dependent and Independent Variables

A moment ago, we discussed the two variables in our experiment - hunger and throwing a ball. But, they are both better defined by the terms 'dependent' or 'independent' variable.

The dependent variable is the variable a researcher is interested in. The changes to the dependent variable are what the researcher is trying to measure with all their fancy techniques. In our example, your dependent variable is the person's ability to throw a ball. We're trying to measure the change in ball throwing as influenced by hunger.

An independent variable is a variable believed to affect the dependent variable. This is the variable that you, the researcher, will manipulate to see if it makes the dependent variable change. In our example of hungry people throwing a ball, our independent variable is how long it's been since they've eaten.

Questions:

If in our example, our dependent variable is the person's ability to judge a king. We're trying to measure the change in judging as influenced by …….. Complete a sentence

If in our example, our dependent variable is the person's perception of a king. We're trying to measure the change in perception as influenced by …….. Complete a sentence

Del Siegle, Ph.D.
Neag School of Education – University of Connecticut
del.siegle@uconn.edu
www.delsiegle.com

Each person/thing we collect data on is called an OBSERVATION (in our work these are usually people/subjects. Currently, the term participant rather than subject is used when describing the people from whom we collect data).

OBSERVATIONS (participants) possess a variety of CHARACTERISTICS.

If a CHARACTERISTIC of an OBSERVATION (participant) is the same for every member of the group (doesn’t vary) it is called a CONSTANT.

Questions:

You examine people having different litracy levels. But do not you think that a characteristic of participants is the same for every member of the group of matric students?

If a CHARACTERISTIC of an OBSERVATION (participant) differs for group members it is called a VARIABLE. In research we don’t get excited about CONSTANTS (since everyone is the same on that characteristic); we’re more interested in VARIABLES. Variables can be classified as QUANTITATIVE or QUALITATIVE (also known as CATEGORICAL).

QUANTITATIVE variables are ones that exist along a continuum that runs from low to high. Ordinal, interval, and ratio variables are quantitative.  QUANTITATIVE variables are sometimes called CONTINUOUS VARIABLES because they have a variety (continuum) of characteristics. Height in inches and scores on a test would be examples of quantitative variables.

Questions:

Tell what ‘scores on a test’ mean? And for our puporse what a test and score mean?

QUALITATIVE variables do not express differences in amount, only differences. They are sometimes referred to as CATEGORICAL variables because they classify by categories. Nominal variables such as gender, religion, or eye color are CATEGORICAL variables. Generally speaking, categorical variables

Questions: You examine people from different walks of life. You examine people belonging to different age groups. You examine people having different litracy levels. Do you think you need categorical variables? Categorical variables are groups…such as gender or type of degree sought. Quantitative variables are numbers that have a range…like weight in pounds or baskets made during a ball game. When we analyze data we do turn the categorical variables into numbers but only for identification purposes…e.g. 1 = male and 2 = female. Just because 2 = female does not mean that females are better than males who are only 1.  Question: As we read that when we analyze data we do turn the categorical variables into numbers but only for identification purposes it does not mean one is better than other. You examine people having different litracy levels; and find for example; 100 matric students and 10 Phd students. Can we say one is not better than other? Question: With quantitative data having a higher number means you have more of something. So higher values have meaning.  You examine people having different litracy levels; and find for example; 100 matric students and 10 Phd students. Can we say having higher number mean higher values?

A special case of a CATEGORICAL variable is a DICHOTOMOUS VARIABLE. DICHOTOMOUS variables have only two CHARACTERISTICS (male or female). When naming QUALITATIVE variables, it is important to name the category rather than the levels (i.e., gender is the variable name, not male and female).

Variables have different purposes or roles…

Independent (Experimental, Manipulated, Treatment, Grouping) Variable-That factor which is measured, manipulated, or selected by the experimenter to determine its relationship to an observed phenomenon. “In a research study, independent variables are antecedent conditions that are presumed to affect a dependent variable. They are either manipulated by the researcher or are observed by the researcher so that their values can be related to that of the dependent variable. For example, in a research study on the relationship between mosquitoes and mosquito bites, the number of mosquitoes per acre of ground would be an independent variable” (Jaeger, 1990, p. 373)

Question: If we say relationship between types of mosquitoes and mosquito bites. So what does it mean? And then we must write ……of mosquitoes…..

Question: If we say relationship between time and mosquito bites. So what does it mean? And then we must write ……of mosquitoes…..

Question: If we say relationship between hunger and mosquito bites. So what does it mean? And then we must write ……of mosquitoes…..

While the independent variable is often manipulated by the researcher, it can also be a classification where subjects are assigned to groups. In a study where one variable causes the other, the independent variable is the cause. In a study where groups are being compared, the independent variable is the group classification.

Question: Your independent variable is the classification of people according to age, literacy and profession but if one variable casuses the other, the independent variable is the cause. Can you say your independent variable is group classification?

Dependent (Outcome) Variable-That factor which is observed and measured to determine the effect of the independent variable, i.e., that factor that appears, disappears, or varies as the experimenter introduces, removes, or varies the independent variable. “In a research study, the independent variable defines a principal focus of research interest. It is the consequent variable that is presumably affected by one or more independent variables that are either manipulated by the researcher or observed by the researcher and regarded as antecedent conditions that determine the value of the dependent variable. For example, in a study of the relationship between mosquitoes and mosquito bites, the number of mosquito bites per hour would be the dependent variable” (Jaeger, 1990, p. 370). The dependent variable is the participant’s response.

Can we say: ‘the penetration of bite per hour would be the dependent variable and pain people feel is the dependent variable’?

The dependent variable is the outcome. In an experiment, it may be what was caused or what changed as a result of the study. In a comparison of groups, it is what they differ on.

Moderator Variable- That factor which is measured, manipulated, or selected by the experimenter to discover whether it modifies the relationship of the independent variable to an observed phenomenon. It is a special type of independent variable.

The independent variable’s relationship with the dependent variable may change under different conditions. That condition is the moderator variable. In a study of two methods of teaching reading, one of the methods of teaching reading may work better with boys than girls. Method of teaching reading is the independent variable and reading achievement is the dependent variable. Gender is the moderator variable because it moderates or changes the relationship between the independent variable (teaching method) and the dependent variable (reading achievement).

Task: you have to prove that both methods of teaching are wrong or in other words neither is effective, so what you have to do?

Suppose we do a study of reading achievement where we compare whole language with phonics, and we also include students’ social economic status (SES) as a variable. The students are randomly assigned to either whole language instruction or phonics instruction. There are students of high and low SES in each group.

Let’s assume that we found that whole language instruction worked better than phonics instruction with the high SES students, but phonics instruction worked better than whole language instruction with the low SES students. Later you will learn in statistics that this is an interaction effect. In this study, language instruction was the independent variable (with two levels: phonics and whole language). SES was the moderator variable (with two levels: high and low). Reading achievement was the dependent variable (measured on a continuous scale so there aren’t levels).

With a moderator variable, we find the type of instruction did make a difference, but it worked differently for the two groups on the moderator variable. We select this moderator variable because we think it is a variable that will moderate the effect of the independent on the dependent. We make this decision before we start the study.

If the moderator had not been in the study above, we would have said that there was no difference in reading achievement between the two types of reading instruction. This would have happened because the average of the high and low scores of each SES group within a reading instruction group would cancel each other an produce what appears to be average reading achievement in each instruction group (i.e., Phonics: Low—6 and High—2; Whole Language:   Low—2 and High—6; Phonics has an average of 4 and Whole Language has an average of 4. If we just look at the averages (without regard to the moderator), it appears that the instruction types produced similar results).

Suppose we do a study of achievements of reform (reforms launched by a king) where we compare whole reforms, and let’s assume that we found that whole reforms worked better than reforms in agriculture sector. In this study, reforms were the independent variable and economic acheivemnt was the dependent variable. Reforms appered to work better as the whole than reforms in one sector alone.

Question: tell the factor which is measured, manipulated, or selected by the experimenter to discover whether it modifies the relationship of the independent variable to an observed phenomenon?

With a moderator variable, we find that the reforms did make a difference, but it worked differently for the two groups on the moderator variable. For example big landlords associated with a king got all benefits but small landlords suffered.  

If the moderator is not used in this study, we would have said that there was no difference in the achievements of reforms.

Tell which moderator is to be used?

Extraneous Variable- Those factors which cannot be controlled.
Extraneous variables are independent variables that have not been controlled. They may or may not influence the results. One way to control an extraneous variable which might influence the results is to make it a constant (keep everyone in the study alike on that characteristic). If SES were thought to influence achievement, then restricting the study to one SES level would eliminate SES as an extraneous variable.

Do you think restricting the effects of reform to big land lords would eliminate an extraneous variable?

Here are some examples similar to your homework:

Null Hypothesis: Students who receive pizza coupons as a reward do not read more books than students who do not receive pizza coupon rewards.
Independent Variable: Reward Status
Dependent Variable: Number of Books Read

High achieving students do not perform better than low achieving student when writing stories regardless of whether they use paper and pencil or a word processor.
Independent Variable: Instrument Used for Writing
Moderator Variable: Ability Level of the Students
Dependent Variable:  Quality of Stories Written
When we are comparing two groups, the groups are the independent variable. When we are testing whether something influences something else, the influence (cause) is the independent variable. The independent variable is also the one we manipulate. For example, consider the hypothesis “Teachers given higher pay will have more positive attitudes toward children than teachers given lower pay.”
One approach is to ask ourselves “Are there two or more groups being compared?” The answer is “Yes.” “What are the groups?” Teachers who are given higher pay and teachers who are given lower pay. Therefore, the independent variable is teacher pay (it has two levels– high pay and low pay). The dependent variable (what the groups differ on) is attitude towards school.

We could also approach this another way. “Is something causing something else?” The answer is “Yes.”
“What is causing what?” Teacher pay is causing attitude towards school. Therefore, teacher pay
is the independent variable (cause) and attitude towards school is the dependent variable (outcome).

Research Questions and Hypotheses

The research question drives the study. It should specifically state what is being investigated. Statisticians often convert their research questions to null and alternative hypotheses. The null hypothesis states that no relationship (correlation study) or difference (experimental study) exists. Converting research questions to hypotheses is a simple task. Take the questions and make it a positive statement that says a relationship exists (correlation studies) or a difference exists (experiment study) between the groups and we have the alternative hypothesis. Write a statement that a relationship does not exist or a difference does not exist and we have the null hypothesis.

We find that the reforms did make a difference, but it worked differently for the two groups.

Write the null or the alternative hypothesis.

Format for sample research questions and accompanying hypotheses:

Research Question for Relationships: Is there a relationship between height and weight?
Null Hypothesis:  There is no relationship between height and weight.
Alternative Hypothesis:  There is a relationship between height and weight.

When a researcher states a nondirectional hypothesis in a study that compares the performance of two groups, she doesn’t state which group she believes will perform better. If the word “more” or “less” appears in the hypothesis, there is a good chance that we are reading a directional hypothesis. A directional hypothesis is one where the researcher states which group she believes will perform better.  Most researchers use nondirectional hypotheses.

We find that the reforms did make a difference, but it worked differently for the two groups. Write a directional hypothesis

We usually write the alternative hypothesis (what we believe might happen) before we write the null hypothesis (saying it won’t happen).

Directional
Research Question for Differences: Do boys like reading more than girls?
Null Hypothesis:  Boys do not like reading more than girls.
Alternative Hypothesis:  Boys do like reading more than girls.

Nondirectional
Research Question for Differences: Is there a difference between boys’ and girls’ attitude towards reading? –or– Do boys’ and girls’ attitude towards reading differ?
Null Hypothesis:  There is no difference between boys’ and girls’ attitude towards reading.  –or–  Boys’ and girls’ attitude towards reading do not differ.
Alternative Hypothesis:  There is a difference between and girls’ attitude towards reading.  –or–  Boys’ and girls’ attitude towards reading differ.boys’