Schacter, S., The psychology of affiliation, 1959, Chapters 2-4.

Chapter 2: Anxiety and Affiliation
In this study the researchers hypothesized that induced anxiety would produce an increase of affiliative tendencies.

In the study they had two conditions -- high anxiety and lower anxiety. In the high anxiety they played up the ominous and expected pain of the electric shock experiment. In the low anxiety they made it seem nearly painless.

They gave their speils to college women, and then asked them rate their anxiety level, and then decide if they prefer being alone or with others before the electric shock tests would begin. Lastly they were given the choice to be let out of the experiment (without credit for their psych class).

Results
Clearly the girls in the high anxiety condition felt more anxiety, and in fact 19% wanted out of the experiment. 63% of the high anxiety condition wanted to remain together, but only 33% wanted to be together in the low anxiety condition.

Chapter 3: The Afiliative Tendencey -- Directionality
Why do anxious people seek the company of other people? Do they seek general people or people of similar plight?

They reran the above experiment (high anxiety), but had two conditions for the together room. In one condition it would be the same people in the test, in the other condition it would be girls waiting to talk to advisors.

The reported level of anxiety was the same in both groups, However, the girls in the "same state" group prefered togetherness, while the other group was indifferent to being with the "other girls" not involved in the test. The results indicate that anxious people want to be with others of similar plight.

Chapter 4: The Affiliative Tendency -- Communication
Why did the anxious girls want to be in a group? Possible explanations are:
1. Escape (get talked out of it by others)
2. Cognitive Clarity (talk about ambigious situation with others)
3. Direct Anxiety Reduction (comfort and support each other, bolster courage)
4. Self-Evaluation: Compare emotions and feelings versus others
5. Indirect Anxiety Reduction (talk about something else to take mind off situation)

Once again they modified the experiment with multiple conditions about what the girls could do in the "togetther room" (Talk about anything, Talk about anything but the experiment, No Talking).
They found that girls preferred the together option for all three conditions. It seems from the data they could rule out #1 as an explanation (no escape with the no-talk option) and #2 (same reason) and #5 (same reason). Therefore more study is needed to see if anxious people prefer being in groups of similar people to evaluate their own feelings against others or merely to provide and receive comfort and support from each other.