Lab Objective: Psychologists often develop hypotheses based upon observations of the world around them, and then systematically collect data to test these hypotheses. In this two-part lab, you will :

In class today, you will do I. You will be responsible for doing II., III., and IV. on your own outside of class (instructions are listed below). Then, next week in class, you will discuss your results and how to write them up in your discussion section. Your paper for this lab will be due no later than the beginning of discussion section, the 4th week of class.

You will be asked to turn in a copy of your raw data (the ratings of your two variables) and your correlation coefficient when you turn in your paper 2 weeks from now. If you used the web page, print out your results. If you computed the correlation by hand bring your calculations.

Many people, including college students, report feeling a lot of stress. Different things stress out different people. What do you think affects you? You will work in groups to pick a stressor, that is, a variable that you think affects your stress levels. It has to be something you can measure, and to which you can assign a numerical value.

The variable your group picks may be something you measure by self-rating, as would be the case if you think that how tired you are feeling affects how stressed you feel. If you used this variable as your stressor, you would have to designate a scale on which to rate how tired you feel each day. For example, the scale could take the following form:

The scale above (known as a "Likert scale") is very subjective. You might want to specify what each category means:

1 = not at all tired: feeling well-rested, didn't yawn the whole day

2 = slightly tired: yawned only a few times, felt mostly rested

3 = somewhat tired: yawned several times, had to sit down to rest more at least once

4 = very tired: had to rest a lot, fell asleep in at least one class, yawned frequently

5 = extremely tired: fell asleep in most or all classes, activities limited by fatigue

Alternatively, the variable you pick may be less subjective, perhaps something you can count. For example, you may think that the number of times your roommate pops his or her gum affects your stress level. In this case, you would count how many times your roommate pops his or her gum. Or, if you were still interested in examining tiredness, instead of using the subjective rating of tiredness (illustrated above), you could use the more objective measure of how many hours of sleep you got the night before.

Whatever your group decides, make sure you all have the same understanding of what the stressor is, and how to rate it. Everyone in your group has to use the same rating scale. Fill out the attached worksheet to specify your stressor.

Every day, for at least 5 of the next 7 days (more is great!), you will keep track of your stress level, and your variable (whatever you pick). You should pick a consistent time in the day to make your stress ratings (e.g., right after you watch the 11:00 news, or just before brushing your teeth before going to bed).

Given that stress is largely a subjective construct (i.e., you are as stressed as you feel), we will use a subjective rating scale to rate stress, and everyone will use the same scale:

1 = No stress

2 = Minimal stress

3 = Moderate stress

4 = Heavy stress

5 = Maximum stress

The easiest way to record the data would be to put three column headings on a sheet of paper, labelling the first column "Date," the next column "Stress" and the third "Stressor" (or what your specific stressor is, e.g., "Instances of gum popping." After recording the date, you will write down two numbers each day: one will be a rating of your stress level, and the other a rating or count of your stressor.

Don't forget to do your ratings, but if you do, do not fabricate (make up) data! Fabricating data is CHEATING. You must collect data on yourself for 5 days, but you have a week.

III. Sharing data

The other members of your group will also keep track of their stress levels and ratings of their stressor. Next week, you must share your data with each other (it would be best to exchange phone numbers or email addresses just in case).

IV. Computing the correlation

Once you have the complete group data, you will compute a correlation between the two variables. A correlation coefficient (as you read about in your text) is a numerical rating of the degree to which the two variables co-vary. It can be negative (which means that when one variable goes up, the other goes down) or positive (which means that when one variable goes up, the other also goes up). The further the correlation coefficient is from zero, in either a positive or negative direction, the higher the correlation between the two variables. A correlation of -1.0 or 1.0 is a "perfect" correlation, meaning you can exactly predict the value of one variable if you know the value of the other variable.

You have many handy options for computing a correlation coefficient. The easiest is to go to the following web site:

Where it says "The observation pairs (x,y)" delete any numbers already there and enter your data. For each pair of data, first enter your predictor, type a space and then enter your stress level. Return and enter the next pair. When you've entered all your pairs, click "submit." Your correlation is the first number that comes after "R =".

Although using the web page is very simple, there are other options for computing the correlation coefficient. If you have a calculator that does statistical functions, it may be possible to use your calculator. If you use a spreadsheet on your computer, there is probably a way of computing a correlation using it too. Virtually any introductory statistics textbook will also include the formula for computing a correlation coefficient by hand.

Compute the correlation, and bring your raw data, your correlation, and any calculations with you to your discussion section the third week of class.

1. List the other members of your group, and how they can be reached:

2. List the variable your group has picked as a potential stressor (describe your variable):

3. Do you think the stressor has a positive relationship with stress (when ratings of your stressor go up, stress level goes up), or a negative relationship with stress (when ratings of your stressor go down, stress level goes up)?

4. The stressor is a variable that (check one):

_____ can be counted

If you checked this option, agree on how precisely you will count it. For example, will you round "Hours of sleep" to the nearest hour? Quarter hour? Five minutes? Provide this information here.

_____ will require subjective ratings

If you checked this option, provide the following information about your rating scale below:

a) What are the minimum and maximum values?

b) What are the "anchors" (verbal labels describing the numerical values)?

5. Discuss your rating scale and make sure you all agree on it, and have a similar understanding of what it means. List any guidelines your group arrives at for describing your stressor: