Vampire off revenants—are common in vampire folklore. Garlic is a common example, a branch of wild rose and hawthorn plant are said to harm vampires, and in Europe, sprinkling mustard seeds on the roof of a house was said to keep them away. Other apotropaics include sacred items, for example a crucifix, rosary, or holy water. Vampires are said to be unable to walk on consecrated ground, such as that of churches or temples, or cross running water. Although not traditionally regarded as an apotropaic, mirrors have been used to ward off vampires when placed, facing outwards, on a door (in
Cross-sectional study as censuses. Cross-sectional studies may involve special data collection, including questions about the past, but they often rely on data originally collected for other purposes. They are moderately expensive, and are not suitable for the study of rare diseases. Difficulty in recalling past events may also contribute bias. The use of routinely collected data allows large cross-sectional studies to be made at little or no expense. This is a major advantage over other forms of epidemiological study. A natural progression has been suggested from cheap cross-sectional studies of routinely collected data which suggest hypotheses, to case-control studies testing them more