Question

A. How well do people remember their past diet? Data are available for 91 people who were asked about their diet when they were 18 years old. Researchers asked them at about age 55 to describe their eating habits at age 18. For each subject, the researchers calculated the correlation between actual intakes of many foods at age 18 and the intakes the subjects now remember. The median of the 91 correlations was r = 0.217. The researchers stated, "We conclude that memory of food intake in the distant past is fair to poor".

Choose the best reason why r = 0.217 points to this conclusion.

Because a correlation of 0.217 indicates a negative association.

Because a correlation of 0.217 indicates a positive association.

Because a correlation of 0.217 indicates a strong association.

Because a correlation of 0.217 indicates a weak association.

Because a correlation of 0.217 indicates no association.

B. Although research questions usually concern a _________, the actual research is typically conducted with a ________.

sample, statistic

population, parameter

sample, population

population, sample

Answer 1

A) CORRELATION COEFFICIENT:

The correlation coefficient, denoted by r, is a measure of the strength of the straight-line or linear relationship between two variables. The correlation coefficient takes on values ranging between +1 and -1. The following holds true:

1. 0 indicates no linear relationship.
2. +1 indicates a perfect positive linear relationship: as one variable increases in its values, the other variable also increases in its values.
3. -1 indicates a perfect negative linear relationship: as one variable increases in its values, the other variable decreases in its values.
4. Values between 0 and 0.3 (0 and -0.3) indicate a weak positive (negative) linear relationship.
5. Values between 0.3 and 0.7 (-0.3 and -0.7) indicate a moderate positive (negative) linear relationship.
6. Values between 0.7 and 1.0 (-0.7 and -1.0) indicate a strong positive (negative) linear relationship.

Thus in our problem, the correlation coefficient r = 0.217. Since it ranges between 0 and 0.3, it indicates a weak positive linear relationship between actual intakes of many foods at age 18 and the intakes the subjects now remember.

Thus the best reason for the researcher to conclude that memory of food intake in the distant past is fair to poor" is "Because a correlation of 0.217 indicates a weak association".

B) Although research questions usually concern a Population, the actual research is typically conducted with a Sample.

​Research question is usually concerned about the population. But it is not feasible to make a complete census of a population because of time and budget constraints. Therefore, a sample of the population is used to make inferences about the whole population.