User`s guide

E-Prime User’s Guide
Appendix A: Timing Test Results
Page A-12
Tests were conducted on a wide range of machine configurations. Sample results provided in
this text are from a representative ‘low-to-mid-range’ class machine* with the following specific
configuration.
• AMD-350MHz Processor
• 64MB Ram
• Windows 98 Operating System
• BSOFT DIG-130 Card
• IOMEGA 250Mb Zip Drive
• 40X CD-ROM IDE
• Not connected to a network
*Results for other classes of machines will be periodically updated on the Psychology Software
Tools website.
Summary of Results
To summarize the timing implications for this particular test machine, the timing is quite good and
will provide valid results for human reaction times. To provide a concrete quantification of the
accuracy on this machine, the timing accuracy depends on the type of test being performed, but
the summary results show that the standard deviation is always below 0.84ms (except for the
mouse response timing). To understand the implications of these results it is useful to see what
the loss of statistical power is, relative to data collected on a “theoretically perfect machine." The
added error of 0.84ms standard deviation to a human reaction time with a standard deviation of
150ms (typical of responses in the 600ms range), increases the variance by 0.0032%. To
comprehend how this might effect the data being collected, it is useful to express this data in
terms of how many additional trials the experimenter must run in order to compensate for the
increased variance. In this particular case, the experimenter would need to run one extra trial per
31,686 trials on this computer relative to running the experiment on a theoretically "perfect timing
computer." In practice, this might amount to one extra trial per year for the typical psychology
laboratory and hence, is negligible.
Test Description Avg
Absolute
Error (ms)
Avg
Delay
(ms)
SD (ms) % Increase in
Measurement
Variance
1 Extra Trial
Required Per
N Trials
Fixed Duration Clock Test
(1-10000ms)
0.134 n/a 0.167 0.0001% 806,158
Varying Duration Clock Test
(+1,+2,+3, Primes)
0.162 n/a 0.235 0.0002% 407,245
Refresh Rate Test (120Hz)
0.271 n/a 0.543 0.0013% 76,427
Keyboard Response Fixed Delay
Test (1-10000ms)
n/a 6.476 0.793 0.0028% 35,744
Keyboard Varying Delay Test
(+1, +2, +3, Primes)
n/a 6.450 0.759 0.0026% 39,021
Keyboard Response Fixed Delay
Test (1-10000ms), Multi-Frame
Stimulus
n/a 6.603 0.843 0.0032% 31,686
Keyboard Varying Delay Test
(+1, +2, +3, Primes), Multi-Frame
Stimulus
n/a 6.723 0.721 0.0023% 43,254
SRBOX Response Fixed Delay
Test (1ms)
n/a 1.252 0.743 0.0025% 40,786
Mouse Response Fixed Delay
Test (1-10000ms)
n/a 92.071 8.264 0.3035% 329
Mouse Response Varying Delay
Test (+1, Primes)
n/a 96.405 7.051 0.2210% 453