Basics

StatsDirect combines numerical tools with help to assist you in the design, analysis, inference and presentation of quantitative research. It is not a substitute for a statistician. The best statistical practice is achieved by co-operation of investigator and statistician, starting at the planning stage of a study. StatsDirect can help an investigator to understand the basics of statistical practice and to carry out the most commonly used analyses. In this way, StatsDirect improves communication between investigator and statistician. We appreciate that many investigators do not have the resources to consult with a statistician; therefore, we have used this help text to address statistical misconceptions that investigators commonly present to us. StatsDirect data input and result screens use as little statistical jargon as possible in order to improve understanding by the non-statistician.

The StatsDirect help system is not meant to replace statistical textbooks or emulate their style of presentation. This help system is designed for on-screen use within StatsDirect. For further reading we recommend that you seek out key references listed in the reference list.

Sections of StatsDirect help relating to common situations are:

• Statistics

• Epidemiology

• Understanding P values and degrees of freedom

• Understanding confidence intervals

• Causality, bias and confounding

• Retrospective vs. prospective studies

• Reference list

• Statistical method selection

• Contacts

SPECIAL POINTS

1. Confidence intervals (CI) are very useful in statistical inference. StatsDirect places strong emphasis on confidence interval analysis. Wherever possible, the most exact method for the CI has been used. Before calculation of a CI a dialogue box asks you to select a coefficient of confidence. The default 95% confidence level is selected routinely when you press the enter key. You can turn off this dialogue box using the options selection of the analysis menu; in this situation a 95% CI is selected automatically.

2. Some of the StatsDirect functions are time consuming. When a process is taking an appreciable amount of time the mouse pointer changes from an arrow to an hourglass and a progress meter is often displayed.