Objectivity in assessing critical sperm characteristics such as concentration, motility and morphology, has been the target of many systems and devices. Methods based on physical principles such as turbidimetry, spectrophotometry, laser Doppler technology, are too imprecise or technically too complicated to be applied routinely in the laboratory. Microscopic images providing photographical, cinematographical or video data acquisition followed by manual or computer-assisted image analysis (CASA) suffer from practical and/or device deficiencies, making them tedious and time-consuming, or unreliable because of confounding factors and uncontrolled artefacts. A single-step computer system using visual evaluation of the microscopic field and manual tracking of sperm movement yields more reliable results, but technician expertise remains essential for correct performance. The scientific basis of multiple errors in semen aspiration, chamber quality, data acquisition and analysis is given. Biased interpretations of results or incorrect handling of statistical data are criticised.

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