That as already discussed, you need a control group to know whether either of the groups were effective at all. You can compare them without a control group but you cannot know whether they are effective compared to "doing nothing". You need to know the baseline, some percent of people are going to report eating less meat, going vegan, etc without viewing either lecture. You need to know these baseline rates to know whether the lecture improved or worsen them.Jebus wrote: ↑Sun Mar 11, 2018 8:23 amYou just explained why long term follow-up is important. No one has yet given a good reason why a control group is necessary. To clarify, I would like someone who is pro control group to clarify exactly what they would do with the control group, i.e. what questions would they be asked? What would be the time interval between questions etc.?
Also just surveying people's impressions on veganism won't tell you much anyways, you won't to know whether it impacted people's behavior. For example after a lecture given by a Jehovah Witness people may have a more positive view of them...but they may be no more likely to join the religion or agree with some aspects of it.