Final answer:
In the experiment with controlled participant education level, the researchers used stratified random sampling to ensure each treatment condition had participants with homogeneous education levels. This method enhances the study's validity by adequately representing subgroups in the sample.
Step-by-step explanation:
In the experiment comparing two treatments, assigning participants to treatment conditions so that each condition has 10 adults with high school diplomas is a method used to control for participant education level. This technique is known as stratified random sampling. Stratified random sampling is a method where the population is first divided into strata with similar characteristics, in this case, education level, and then a random sample is taken from each stratum to ensure representation.
Looking at the various examples provided:
- The soccer coach uses stratified random sampling by creating age categories and selecting players from each.
- The pollster utilizes cluster sampling by choosing all personnel from certain companies.
- The educational researcher is again using stratified random sampling by selecting equal numbers of male and female teachers.
- Random assignment in an experiment ensures each participant has an equal chance of being placed in any given group, bolstering the validity of the conclusion.
- The instructor who picks students from each math class is employing cluster sampling.
- Choosing a random sample is effective because it gives everyone an equal chance of being part of the study, enhancing the study's validity.