The Experiment:
We seek to determine how good folks are at distinguishing between different masses. Accordingly, we set out 5 - 10 masses in the 50 - 150 g range and a known or reference mass of 100 grams. We label the rocks in random order, 1, 2, 3, . . . , 9 say. (Do not label them in increasing mass order!) And we identify the known mass and its actual mass for the participants.
We ask participants to indicate whether the sample rocks are of greater mass than the known mass. We provide a slip of paper in which we could ask them some information for later references, e.g., their major, their position (student - undergraduate or graduate, faculty and discipline, administrative, staff, etc.) Do not ask for names unless, say, you wish to have a contest for "best" guesses.
The real information we want is their opinion on whether the mass of the rocks, numbered 1, 2, . . . , 9, are more than the sample/known mass. So we provide a form such as the following:
Sample Rock Number 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Check if mass is more | | | | | | | |
than 100 g
We set the collection table out for whatever time we believe reasonable to get sample data - one week will be sufficient especially if there is a sign, say with words like "Rock-A-Rama," "Let's Rock," "Science Experiment," or "Which Major is More Perceptive," and some catchy graphics.
Once we have collected the data, we compute the percent of respondents who say that a given rock has mass greater than the 100 g standard mass. We plot this percent vs. the actual mass of the given rock.