Iconic memory is a type of memory that holds visual information for about half a second (0.5 second). To demonstrate this type of memory, participants were shown three rows of four letters for 50 milliseconds. They were then asked to recall as many letters as possible, with a 0-, 0.5-, or 1.0-second delay before responding. Researchers hypothesized that longer delays would result in poorer recall. The number of letters correctly recalled by 18 subjects was recorded.

15. Identify the population of interest.

16. Identify the sample.

17. Identify the independent variable(s).

18. Identify the dependent variable(s).

A researcher is interested in how perceptions of global warming influence consumer spending. He selects a sample of 10 environmentalists with strong perceptions of global warming and has them report how much they spend on a variety of "typical" items. These "typical" items were categorized as detrimental, safe, or helpful to the environment.

19. Identify the population of interest.

20. Identify the sample.

21. Identify the independent variable(s).

22. Identify the dependent variable(s).