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| observations (such as measurements,genders, survey responses) that have been collected |
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| a collection of methods for planning studies and experiments, obtaining data, and then organizing, summarizing, presenting, analyzing, interpreting, and drawing conclusions based on the data |
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the complete collection of all elements (scores, people, measurements, and so on) to be studied. The collection is complete in the sense that it includes all subjects to be studied
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| Collection of data from every member of a population |
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| Subcollection of members selected from a population |
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| a numerical measurement describing some characteristic of a population. |
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| a numerical measurement describing some characteristic of a sample. |
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numbers representing counts or measurements.
Example: The weights of supermodels |
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can be separated into different categories that are distinguished by some nonnumeric characteristic
Example: The genders (male/female) of professional athletes
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result when the number of possible values is either a finite number or a ‘countable’ number
(i.e. the number of possible values is
0, 1, 2, 3, . . .)
Example: The number of eggs that a hen lays |
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result from infinitely many possible values that correspond to some continuous scale that covers a range of values without gaps, interruptions, or jumps Example: The amount of milk that a cow produces; e.g. 2.343115 gallons per day |
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| Nominal Level of measurement |
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characterized by data that consist of names, labels, or categories only, and the data cannot be arranged in an ordering scheme (such as low to high)
Example: Survey responses yes, no, undecided |
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| Ordinal Level of measurement |
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involves data that can be arranged in some order, but differences between data values either cannot be determined or are meaningless
Example: Course grades A, B, C, D, or F |
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| Interval Level of measurement |
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like the ordinal level, with the additional property that the difference between any two data values is meaningful, however, there is no natural zero starting point (where none of the quantity is present)
Example: Years 1000, 2000, 1776, and 1492 |
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| Ratio Level of measurement |
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the interval level with the additional property that there is also a natural zero starting point (where zero indicates that none of the quantity is present); for values at this level, differences and ratios are meaningful
Example: Prices of college textbooks ($0 represents no cost) |
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| categories with some order |
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| differences but no natural starting point |
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| differences and a natural starting point |
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Voluntary response sample
(or self-selected sample)
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| one in which the respondents themselves decide whether to be included |
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| observing and measuring specific characteristics without attempting to modify the subjects being studied |
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| apply some treatment and then observe its effects on the subjects |
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| data are observed, measured, and collected at one point in time. |
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Retrospective (or case control) study
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| data are collected from the past by going back in time. |
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| Prospective (or longitudinal or cohort) study |
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| data are collected in the future from groups (called cohorts) sharing common factors. |
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| occurs in an experiment when the experimenter is not able to distinguish between the effects of different factors |
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| subject does not know he or she is receiving a treatment or placebo |
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| groups of subjects with similar characteristics |
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| Completely Randomized Experimental Design |
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| subjects are put into blocks through a process of random selection |
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| Rigorously Controlled Design |
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| subjects are very carefully chosen |
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| repetition of an experiment when there are enough subjects to recognize the differences from different treatments |
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| use a sample size that is large enough to see the true nature of any effects and obtain that sample using an appropriate method, such as one based on randomness |
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| members of the population are selected in such a way that each individual member has an equal chance of being selected |
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| subjects selected in such a way that every possible sample of the same size n has the same chance of being chosen |
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selection so that each
individual member has an
equal chance of being selected |
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Select some starting point and then
select every k th element in the population |
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| use results that are easy to get |
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subdivide the population into at
least two different subgroups that share the same characteristics, then draw a sample from each subgroup (or stratum) |
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divide the population into sections
(or clusters); randomly select some of those clusters; choose all members from selected clusters |
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| the difference between a sample result and the true population result; such an error results from chance sample fluctuations |
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sample data are incorrectly collected, recorded, or analyzed (such as by selecting a biased sample, using a defective instrument, or copying the data incorrectly)
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