A health magazine recently reported a study in which researchers claimed that

iron supplements increased memory and problem-solving abilities in a random sample of college women. All of the women took memory and problem-

solving tests at the beginning of the study, then took iron supplements, and then took the same tests again at the end of

the study.

A researcher conducts a study of the effects of amount of sleep on

creativity. The researcher collected (ratio) creativity scores for four levels

of sleep (2 hours, 4 hours, 6 hours, and 8 hours) for N = 20 subjects.

A researcher conducts a study of the effects of amount of sleep on

creativity. The researcher collected (ordinal) creativity scores for four levels of sleep (2 hours, 4 hours, 6

hours, and 8 hours) for N = 20 subjects.

People with anxiety disorders are selected to participate in a study on a new drug for the treatment of this disorder. The researchers know that the drug is effective in treating this disorder, but they are concerned with possible side effects. In particular, they are concerned with the effects of the drug on cognitive abilities. Therefore, the ask each subject to identify a family member or friend who is the same gender as the subject and who is of a similar age as the subject but who does not have an anxiety disorder. The researchers then administer the drug to those with the disorder and measure cognitive functioning in both groups.

Imagine I conducted the following experiment: I used gender as a non-manipulated independent variable and measured performance in my class. I measured performance by ranking everyone in the class, giving the person with the highest grade a 1, the person with the 2nd highest grade a 2, etc. Which statistic would I use to determine any differences in performance between these two groups?

Suppose that we carried out a quasi-experiment on the students in this Experimental Methods class. We wanted to determine if females spent more time studying for this course than did males. There were 20 females and 6 males in the class.

So, every day for a period of three weeks, we asked each student to write down the number of hours that he or she spent studying for his course. We totaled the hours for each student. Then we used a statistical test to see if there was a significant difference.

In a study, a research measures the preference of men and women for two brands of frozen pizza (one low-fat and one regular) based on the number of

1-inch pieces of each type of pizza eaten when both types were available

to the participants.

A psychologist would like to know how much difference there is between the problem-solving ability of 8-year old children versus 10-year old children. A random sample of 10 children is selected from each age group. The children are given a problem-solving test in which each question contributes the same amount to the overall score.

A researcher is investigating the relation between reaction time and room temperature. A sample of N=16 subjects is obtained and each person’s reaction time is measured in a 70° room and again in a room where the temperature is 95°. On average, this sample showed a reaction time that was 45 milliseconds faster in the 70° room.

A researcher conducted an experiment on the effects of a new drug on depression. The researcher had a control group that

received nothing, a placebo group, and an experimental group that received the drug.

A depression inventory that provided a measure of depression on a 50-point scale was used (50 indicates that an individual is

very high on the depression variable).

Researchers at a food company are interested in how a new ketchup made from green

tomatoes (and green in color) will compare to their traditional red ketchup. They are worried that the green color will adversely affect the

tastiness scores. They randomly assign subjects to either the green or red ketchup

condition. Participants indicate the tastiness of the sauce on a 20-point scale. Tastiness scores

tend to be skewed.

A researcher is testing the effectiveness of a blood-pressure medication compared to a placebo using a double-blind procedure. Two samples of subjects are obtained (n=25 each) and divided into the medication group and the placebo group. Each person’s blood pressure is measured before beginning the medication. After 3 weeks, each person’s blood pressure is measured again. The researcher records the amount of change for each individual and compares the two groups.

A researcher was interested in whether massed or spaced studying has a greater

impact on grades in a course. The research had her class study for 6 hours all in one day for one exam (massed study condition). She had them study for 2 hours each day for 3

days for another exam (3-day spaced condition). Last, she had them study for 1

hour a day for 6 days for a third exam (6-day spaced condition). Each exam score was

based on 100 points.

You notice at the gym that it appears that more women tend to work out together, whereas

more men tend to work out alone. To determine whether this

difference is significant, your collect data on the workout

preferences for a sample of men and women at your gym.

A common science-fair project involves testing the effects of music on the growth of plants. Of one of these projects, a sample of 24 newly sprouted bean plants is obtained. These plants are randomly assigned to four treatments, with n = 6 in each group. The four conditions are: rock music, heavy metal, country, and classical. The dependent variable is the height of each plant after 2 weeks.

A researcher is examining the effect of sleep deprivation on basic mental processes. A sample of 8 subjects is obtained. These subjects agree to stay awake for a total of 48 hours. Every 12 hours the researcher gives each subject a series of arithmetic problems as a test for mental alertness. The number of problems worked correctly in 10 minutes is recorded for each subject.

A researcher conducts a study of the effects of amount of sleep on

creativity. The researcher collected ordinal creativity scores for four levels

of sleep (2 hours, 4 hours, 6 hours, and 8 hours) for N = 20 subjects.

In a study of the effects of stress on illness, a researcher tallied the

number of colds people contracted during a 6-month period as a function of the amount of stress they reported during that same time period. There

were three stress levels: minimal, moderate, and high stress.

A researcher is attempting to determine the effects of practice and gender on a timed task. Participants (30) in an experiment are given a

computerized search task. They search a computer screen of various characters and

attempt to find a particular character on each trial. When they find the designated

character, they press a button to stop a timer. Their reaction time (in seconds) is recorded. Subjects practice for 2, 4, or 6 hours and are

either female or male.

A researcher is attempting to determine the effects of practice and gender on a timed task. Participants (30) in an experiment were given a computerized search task. They searched a computer screen of various characters and attempt to find a particular character on each trial. When they found the designated character, they pressed a button to stop a timer. Participants in each group were rank ordered by their reaction time (in sec), with the fastest reaction time assigned to 1st place. Subjects practiced for 2, 4, or 6 hours and were either female or male.

A researcher is interested in whether studying with music helps or hinders the learner. To

control for differences in cognitive ability, the researcher decides to use a within-subjects

design. He selects a random sample of participants and has them study different

material of equal difficult in both the music and no music conditions. Next, the students take a

20-item quiz on the material. The study is completely counterbalanced to control for order effects. The data are measured on an interval –

ratio scale and are normally distributed.