Conduct Web experiments using PHP, Part 2
By Paul Meagher2005-03-18
Envisioning your results
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You can use the poisson distribution to simulate the data that you might observe if you conducted your Web offer study. To select the lambda parameter values to use, you may find it easier to create bar charts of the possible outcomes by selecting the lambda parameter values and trial parameter values required to reliably reproduce the bar chart that you deem the most likely outcome of your Web experiment.
Figure 1. A likely outcome
This bar chart (in Figure 1) reflects the theory that the IMAGE factor and TEXT factor will each exert an effect. No interaction between the factors is expected. You expect the two effects associated with your factor levels to combine in an additive manner.
You will often find it useful to engage in data simulation and graphing as part of the planning phase of a Web experiment. The exercise can serve to clarify data-analysis issues that you might not have anticipated. Issues related to the power of your experiment and the sample size required to detect differences can also be tackled if you have a simulation and graphing tools you can use to explore possible outcomes.
Tutorial Pages:
» Categorical data analysis
» 2x2 contingency tables
» Sampling model
» Discrete probability distributions
» Binomial sampling model
» Poisson sampling model
» Envisioning your results
» Eliciting your prior distribution
» Model fitting with chi-square
» Null effects model
» Independence model
» Prior model
» DOE explorer
» Explorer output
» Conclusions
» Resources
First published by IBM developerWorks
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