Give reasons why there can be problems with within-groups designs.

-  Carryover effect

-  Practice effect.

Explanation:

In within groups-design, a group of research subjects will be put into more than one different conditions / activities in order to measure the effect of each conditions/activities.

For example:

Let's say  that a group of subjects is gathered for a 1 month long research. In the first two week, the subjects will be asked to follow a jogging regiment while in the second week the subjects will be asked to follow a swimming regiment.

Researchers want to measure which activities will be beneficial for their cardiovascular health.

There are a couple of problems in this type of research designs:

1. Carryover effect

In the experiment above, the health benefit that the subjects experience from jogging might be carried over and influence the results of the swimming period. This made the subjects started their second period of research in a better health than when they start at first.

This is called the carryover effect. This made it hard for researchers to truly know how much effect only swimming would provide since the data is mixed by the benefit from joggings.

2. Practice Effect.

If the subjects have done similar activities (jogging or swimming)  in the past, their body will more likely become conditioned to do those activities and it would not experience as big of a transformation compared to the subjects that never did it before.

the earthquake in haiti was a magnitude of 7.0 according to the u.s geological survey yet the smaller earthquake in haiti killed more than 200,000 and left more than 1.2 million people homeless. the chile earthquake was a magnitude of 8.8 and 500 times more stronger but chile's earthquake only injured 712 people.