An issue that causes some discussion and debate is the number and type of questions that may be asked during a lecture. In a previous post giving advice for speakers I suggested that questions can be used as a mechanism for getting a talk back on track if a nervous speaker starts presenting the material too quickly (a common mistake). This mechanism can be used by the speaker if they realise that things aren’t going to plan or by audience members who are experienced speakers and who recognise a problem. Due to this a blanket ban on questions during a talk will only work with experienced speakers who have planned their talk well.
There are different styles of presentation favoured by different speakers. Some are determined by the nature of the topic (an example that I have seen cited is topics that are very contentious which would lead to a debate if questions were permitted during the talk), but for computer science I think that questions during the talk can always work well. To a certain extent the fact that code either works or doesn’t limits the scope for debate.
Probably the major factor that determines the utility of questions is the size of the audience. If you have an audience of less than 50 people then a conversational approach can work, if you have less than 200 people then a reasonable number of questions can be accepted. But as the audience size increases above 300 the utility of questions approaches zero. If the majority of people who might want to ask questions are unable to do so due to lack of time then the value of allowing any questions diminishes. For the largest audiences there probably isn’t any point in having question time.
Another major factor determining which style works best is where the speaker has had experience speaking. Most of my speaking experience is with less formal meetings (such as local LUGs) and in countries with an informal attitude towards such things (Australia, the US, and The Netherlands). A speaker who has primarily spoken for universities such as Cambridge or Oxford (which seem to have a very formal style and questions strictly reserved for the end) or who has come from a country such as Japan(*) where it’s reported that the audience are obliged to show respect for the speaker by being quiet will probably expect questions only at the end and may flatly reject questions during the talk. A speaker who has a background speaking for less formal audiences will expect a certain number of questions during the course of the talk and may plan the timing of their talk with this in mind. When I plan a talk for a one hour slot I plan at most 30 minutes of scheduled talking (IE covering my notes) expecting that there will be 15 minutes of questions along the way and another 15 minutes of questions at the end. Often with such plans my talks run over-time. Of course this means that people who have mostly had experience speaking to smaller and less formal audiences will find it exceedingly difficult to give talks to larger audiences. This may be an incentive for having more formal arrangements for LUG talks to increase the skills of speakers.
The next issue is what level of contentious questions is acceptable. I believe that if you have a disagreement with points that the speaker is making (and have some experience in the field in question) and the audience is not particularly large then one hostile question is acceptable – as a speaker it’s reasonable to refuse to take any further questions from an audience member who has asked one hostile question. Another category of question is the challenging question (not to be confused with a hostile question), for example describing in one sentence what your business requirements are and asking how the topic being discussed will apply to that business requirement. One of the most useful questions I have been asked during a SE Linux talk was concerning the issue of backups of file security contexts, it was presented in a challenging way and the answer that I gave was not nearly as good as I could give now (the code base has improved over the last few years in this regard) – but I think that everyone learned something so that validated the question.
In smaller groups there may be some heckling when the speaker is a well known member of the group, I don’t think that this is a problem either as long as it only consumes a tiny fraction of the time (maybe 20-30 seconds at the start). For larger audiences or for speakers who don’t know the audience well heckling is generally a bad idea.
(*) When speaking in Japan I had a lot of audience interaction. I’m not sure if this is an indication of the Japanese culture changing in this regard, the fact that translation problems forced some interaction, or the audience was showing respect for the Australian culture by asking questions.