Some of the erroneous readings could be due more to human carelessness than to the physical properties of the tape. And the 5 readings that were too high? Maybe the tape bunched up when it was placed on the board. Perhaps the 25 readings that were too low resulted from stretching the tape inappropriately. In our example, the cloth measuring tape produced a number of readings that were either greater than or less than the actual length of the board. Even simple tasks of physical measurement involve measurement error, either due to the measuring tool itself or the way it is used by the person who is doing the measuring. The greater the error, the lower the reliability of measurement. In all forms of measurement there is some degree of measurement error. Sources of Error that Detract from Reliability But one should never draw strong conclusions or make significant decisions about individuals with tests that do not meet the. It is possible to draw tentative conclusions about the relation between psychological variables when the tests show reliabilities below.
80, while good measures of intelligence and cognitive abilities often show reliabilities above. Good personality tests regularly show reliabilities above. 70 is often suggested as a minimum level of acceptable reliability. (It is possible to find negative values for reliability correlations, but when this happens something is seriously, seriously wrong.) There is no one standard for acceptable reliability, but. It is enough to know that Pearson correlation coefficients of reliability nearly always range between 0 and 1.00. There's no need to explain here how it is computed you can look that up if you like. In psychological measurement we like to quantify the amount of reliability of a test with a statistic called the Pearson correlation coefficient.
As physics developed more reliable methods of measurement, we have been able to improve the measurement precision and accuracy to enable remarkable technological achievements, from producing nuclear energy to connecting the world through the Internet to safely flying more than 8 million people through the sky each day.
Modern physics has depended on various standards of distance, defining a meter in 1960 as the distance between two ends of a particular platinum-iridium bar stored under controlled conditions and in 1983 as the distance traveled by light in a vacuum in 1 / 299,792,458th of a second. 1120 the king of England declared that the standard of length would be called a yard, defined by the distance from the tip of his nose to the end of his outstretched arm. These standards have changed over of the history of measurement. For physical properties, this problem has been successfully handled by simply defining the three basic units of measurement (length, mass, and time) according to agreed-upon standards.
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