Response Time Measurement

One of the more technical concerns about Web-based methods deals with response or even reaction time measurement. How can these times be accurate if the computer equipment is not standardized and calibrated, and if the response is transferred over a fragile net connection? The simple answer is: The noise is small enough to detect relative differences in a proper design, even with the weaker techniques of Internet-based response time meas urement, like JavaScript. Reips, Morger, and Meier (2001) demonstrated in an experiment on the previously established list context effect with a Web and a lab condition that an effect is detectable on the Web using JavaScript time measurement. However, for the same number of participants, the power to detect effects is lower on the Web. Fortunately, as mentioned earlier, it is also much easier to recruit many participants on the Web.

One of the ways to measure response times is via JavaScript. Because JavaScript is a "client-side" language (it does not run on the server, but on the participants' computers), depending on the exact JavaScript methods used in the scripts, OS, browser type, browser version, and other software running on the client, there is a probability for variance in timing and technical problems with JavaScript. Accumulating technical interactions with JavaScript can even lead to crashes of browsers and computers (for an experiment showing that using JavaScript in a Web experiment will lead to a 13% higher overall dropout rate compared to the same Web experiment without JavaScript, see Schwarz & Reips, 2001). The likelihood for problems seems to decrease, though, with newer browsers and newer OS versions that obviously adapt well to the problems.

A second crude way of measuring response times is to calculate the time differences of when materials are accessed on the Web server. Scientific LogAnalyzer (Reips & Stieger, 2004; see Using Web-Based Methods: An Example, this chapter) includes a routine to calculate these times from servers' log files.

So, is there any way to accurately measure reaction times via the Internet? There is: Eichstaedt (2001) developed a Java-based method for very accurate response time measurements. A clever combination of applets ensures continuous synchronization and calibration of timing between server and client, which minimizes timing inaccuracies produced by the Internet.

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