Select all designs which describe an observational study that is not a survey: *200 voters are randomly selected and asked how they will vote in an upcoming election.

* 60 pieces of lumber are randomly selected. Half of those are randomly assigned to be treated with a new dealer. 3 months later the level of rotting in the pieces is recorded.

* 100 pregnant women are randomly selected. For 8 weeks. the level of iron in their blood and their vital signs are recorded.

*400 incoming 6th grade students are randomly selected. Researchers record their results on a reading test at the beginning and end of the school year and compare the level of improvement seen in students at elementary schools to students at middle schools.

*300 people apply to test a new mattress. 100 of these customers are selected randomly to receive the new mattress and the others are given an older version. After 6 months they are asked to rate their satisfaction with the mattress.