Hello Science Buddies,
My question has five parts and it begins on your "Sample Size: How Many Survey Participants Do I Need?" page. The last line above the table states, "For the most part though, the 1/√ N approach is sufficient."
1) Is the symbol before the variable a square root sign (maybe called a radical)?
2) If so, have I completed these problems correctly?
Located the square root of the variable and then divided one by the result. (Parenthesis show the #'s the % applies too.)
1/√63 = 0.126 or 12.6% Margin of Error (Year 1 & 2 = rate of words per minute 105, 121, --, --)
1/√47 = 0.146 or 14.6% Margin of Error (Year 2 = rate of words per minute 104, 123, --, 93)
1/ √16 = 0.25 or 25% Margin of Error (Year 1 = rate of words per minute 106, 119, 93, --)
3) How should an experiment address unusable trials? (For instance, several of the tests were interrupted, in a couple the background noise interfered with the audio recording, one reader had no college education, and two readers were not wearing their glasses during the experiment so the student was unable to use those trials.) She noted it in the log notes and on the data chart (47 /54 trials) in her log book, but I didn't know if it should be recorded elsewhere.
4) Generally speaking, what Margin of Error would be considered appropriate for a 6th grade student project at a competitive level?
5) Over two years, four different reading methods were tested on three different adult populations. The first two methods were repeated each year, giving larger overall trial sizes. The last method had 47 trials, which seems a decent number, but the third method only had 16 trials. Next year, she is planning on testing all four methods on two different child populations (she is forced to combine two of the populations) and had planned on comparing the results to prior years. Should the third trial be included in the comparison, or should it be dropped because the trial number is so small. Or does it matter at all because even with 63 trials, the Margin of Error means the results are too close to state with reasonable certainty that method two provides the best results. (Her dependent variables were TIME and ERROR--and the Error rates were even closer!)
Method: 1 2 3 4
Year One: 106 119 93 --
Year Two: 104 123 -- 93
= Trial #s: 63 63 16 47
Thank you so much for your help!