In a Study Comparing Two Nonequivalent Groups, a Selection by History

question 12

Multiple Choice

In a study comparing two nonequivalent groups, a selection by history confound occurs when

• A)some event intervenes between pretest and posttest and affects just one of the groups
• B)some event intervenes between pretest and posttest and affects both selected groups equally
• C)selection influences one of the groups and history influences the other
• D)some historical event causes a failure of the random assignment procedure

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Definitions:

Macrophages

A type of white blood cell part of the immune system, responsible for detecting, engulfing, and destroying pathogens and dead cells.

Null Cells

Lymphocytes that lack surface markers distinctive of T or B cells, often associated with natural killer cell activity.

Variable Regions

Parts of antibodies that differ from one antibody to another, enabling them to bind to a specific antigen.

T-cell Receptors

These receptors on the surface of T-cells recognize and bind to antigens presented by other cells, initiating an immune response.