Valid Sample Size?

How many random golfers would I have to survey to find out how long a round of golf takes? (Lets pretend the sample really is random). If I survey 20 random golfers at my local country club and found that the average time to play a round was 4 hours, is this significant. Lets say that 1000 rounds every month are played there. What is my population, 1000? Does the variance in their response limit the sample size needed to get me say 95% confident? For example if the first 18 golfers all said it took them 3 hours and 45 minutes to play, wouldn't that decrease the sample size I need based on the consistency of the answers?

Valid Sample Size?
Assuming you are only using 1 golf course (since every course is different and thus would take a different time to play)...





I would think that a sample of a random survey of 60 different tee times for each day surveyed you wanted to know, surveyed over 3 weeks would be 90+% accurate barring inclement weather... (i.e. If you wanted to know for Mondays then 20 tee times, randomized from different times of the day, for each of 3 weeks)...





You would likely only need to do 5 days of the seven for the full 3 weeks should you want to know for each day since your data could be inferred to the other 2 days with good accuracy...





The big things that I would think that would skew the averages would be:


1) tourneys since some are 'party' times (with heavy drinkers and once a year golfers) and other tourneys are serious events (which tend to reduce alcohol consumption and play somewhat faster),


2) and long weekends since they tend to bring heavy drinkers and slow play down





Lastly, don't forget that what happens this year may or may not hold true for next year... social habits change, faster greens when reseeded, adding a washroom mid-course etc... all affect play time...
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Reply:You aren't putting all the needed factors into play here. Did you survey all the people on the same day, same week, same season? Does weather have an effect? Does it take longer in the summer because of the heat? If it's raining, do they play? Does it affect the time to do a round. Which hole are you surveying? All they all equal? (Obviously not since each would have a different par). You might even have to go through several years of sample if, for example, you have mild and hard winters.