In addition to understanding the logic of the experimental method you will also need to understand the language that accompanies it. So let's take each concept listed on the Quick Reference Guide in turn and where possible, link it to the word search puzzle experiment.
The first thing on the quick reference guide is the Experimental Hypothesis, which you may see denoted as the H1. As the definition states it’s the prediction of the outcome of the experiment.
Now the hypothesis is the starting point in the process of experimentation, so when we were thinking about a simple experiment that our students could do, we needed an idea that we could test; and this is what we came up with.
High levels of teacher presence in PC lab 1 will cause students to perform a word search puzzle more quickly than students in PC lab 2.Now because we’ve predicted the way in which behavior will change, i.e. it will get faster, we’ve actually formulated a One-Tailed Experimental Hypothesis.
If we had simply stated that high levels of teacher presence will cause students in PC lab 1 to perform a word search puzzle differently than students in PC lab 2. We would have formulated a Two-Tailed Experimental Hypothesis because all we’re saying here is that the behavior of interest will change.
The decision to choose a one-tailed or a two-tailed hypothesis depends on how confident you feel in predicting the way that behavior will change. We were confident enough to go for a one-tailed experimental hypothesis because a large body of research evidence suggests that the presence of others will improve performance on simple tasks.
Another type of hypothesis you need to be aware of is the Null Hypothesis sometimes denoted as the H0, now this simply states that any observed differences between groups were down to chance. The idea behind this is that depending on the result of statistical testing at the end of the experiment you will either reject or retain the null hypothesis. Put simply the bigger the difference between groups, the less likely that the difference is down to chance and the more likely you are to reject the null hypothesis.
Continuing with the quick reference guide let’s have a look at the Independent Variable (the IV). This is the one factor that is different between conditions. Now the IV is the thing that you as the experimenter manipulate in order to see if it causes a change in behavior and as already mentioned it was level of teacher presence.
So what about the Dependent Variable (the DV)? The aspect of behavior measured? Again as previously mentioned it was the time taken in seconds to complete the word search puzzle.
Hopefully you are beginning to see that although the experimental method uses unfamiliar terms like the H1, H0, IV and DV the things they allude to are not actually that complicated.
Let’s go back to the logic of the experimental method and highlight the independent and dependent variables.If two groups of participants are equal in all respects save one ( the independent variable) and are not similar in respect of a behavior that is being measured (the dependent variable) then the difference between them must be attributable to the one way in which they were different (the independent variable).
Now, remember I said lets accept for the time being that the two groups of participants doing the word search puzzle are equal in all respects save one. Well clearly this is impossible to maintain when dealing with human subjects for the simple fact that we are not clones, we’re all different and we bring our individual differences with us when we take part in an experiment.
For instance, some of the students will have had more sleep than others and this may have affected their performance i.e. they didn’t finish the word search puzzle as quickly as they might have done if they'd had a proper night’s sleep.
Now this shouldn’t be a problem providing we are only talking about one or two people, and this kind of thing is referred to as a random error because things like number of hours sleep vary randomly in a population of people and it’s something that cannot be eliminated.
It’s when random errors become constant errors that you’ll find yourself saying Houston we have a problem.
Remember the cornerstone of the scientific method is to establish cause and effect and we do this by manipulating the independent variable to see what effect it has on the dependent variable. In our case we manipulated level of teacher presence to see what effect in had on the time taken to complete the word search puzzle.
Now imagine if it transpired that all the students in PC lab 2 had been to the same party the night before and only had on average 2 hours sleep? Whereas; all the students in PC lab 1 had fallen out with the person throwing the party so they didn’t go and so they ended up having a normal night’s sleep.
You now have no way of knowing whether students in PC lab 1 performed the word search puzzle more quickly because of level of teacher presence (the IV); or whether they performed the puzzle more quickly because they’d had more sleep and as such were more alert.
In this example sleep has become a Confounding Variable. It’s confounded your results and the experiment is ruined. This somewhat frivolous example was used to introduce you to another integral aspect of the experimental method i.e. control.
In the experimental method we accept that random error exists. We also accept that random error produces extraneous variables. We must, therefore, always do our best to ensure that extraneous variables do not become confounding variables.
The simplest way to do this is to randomly allocate people to different conditions. So in our sleep example for instance, random allocation would ensure that all the party going tired people don't end up in the same group.
This leads us nicely into the 3 main types of experimental design because as you’ll see each has strengths and weaknesses in relation to control issues. Experimental design simply refers to the way in which participants are deployed during the experiment.
Before we look at the 3 designs, however, I just want to quickly outline the difference between the experimental group and the control group. The experimental group is where you expect the predicted behavior change to occur (in our case PC Lab 1 i.e. high level of teacher presence) and the control group acts as the baseline so that this change can be assessed (PC Lab 2 i.e. low level of teacher presence). OK on to the 3 main types of experimental design.