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Definition
| 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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| Consists of numbers representing counts of measurements. |
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| Consists of names or labels that are not numbers representing counts or measurements. |
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Definition
Result when the number of possible values is either a finite number or a "countable" number. (That is, the number of possible values is 0 or 1 or 2, and so on).
The number of eggs that hens lay are discrete data because they represent counts. |
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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.
The amount of milk from cows are continuous data because they are measurements that can assume any value over a continuous span. |
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| Nominal Level of Measurement |
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Definition
Characterized by data that consist of names, labels, or categories only. The data can not be arranged in an ordering scheme (such as low to high).
Eye colors |
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| Ordinal Level of Measurement |
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Definition
If they can be arranged in some order, but differences (obtained by subtraction) between data values either cannot be determined or are meaningless.
Course grades
Military Ranks |
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| Interval Level of Measurement |
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Definition
It is like the ordinal level, with the additional property that the difference between any two data values is meaningful. However, data at this level do not have a natural zero starting point (where none of the quantity is present).
Temperatures
Years |
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| Ratio Level of Measurement |
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Definition
This is 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 both meaningful.
Distances
Prices |
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Definition
| When you observe and measure specific characteristics, but we don't attempt to modify the subjects being studied. |
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| In an experiment, we apply some treatment and then proceed to observe its effects on the subjects. (Subjects in experiments are called experimental units). |
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| A sample of n subjects that is 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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| Members from the population are selected in such a way that each individual member in the population has an equal chance of being selected. |
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| Involves selecting members from a population in such a way that each member of the population has a known (but not recessarily the same) chance of being selected. |
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| We select some starting point and then select every kth (such as every 50th) element in the population. |
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| We simply use results that are very easy to get. |
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| We subdivide the population into at least two different subgroups (or strata) so that subjects within the same subgroup share the same characteristics (such as gender or age bracket), then we draw a sample from each subgroup (or stratum). |
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Definition
| We first divide the population area into sections (or clusters), then randomly select some of those clusters, and then choose all the members from those selected clusters. |
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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 form the past by going back in time (through examination of records, interviews, and so on). |
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| Prospective (or Longitudinal or Cohort) Study |
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Definition
| Data are collected in the futire from groups sharing common factors (called cohorts). |
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Definition
| Occurs in an experiment when you are not able to distinguish among the effects of different factors. |
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Definition
| A graph consisting of bars of equal width drawn adjacent to eachother (without gaps). The horizontal scale represents classes of quantitative data values and the vertical scale frequencies. The heights of the bars correspond to the frequency values. |
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| Relative Frequency Histogram |
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Definition
| Has the same shape and horizontal scale as a histogram, but the vertical scale is marked with relative frequencies (as percentages or proportions) instead of actual frequencies. |
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Definition
| Ogives are useful for determining the number of values below some particular value. It is a line graph that predicts cumulative frequencies. It uses class boundaries along the horizontal scale, and cumulative frequencies along the vertical scale. |
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Term
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Definition
| Consists of a graph in which each data value is plotted as a point (or dot) along a scale of values. Dots representings equal values are stacked. |
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| Stemplot (or stem-and-leaf plot) |
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Definition
| Represents quantitative data by separating each value into two parts: the stem (such as the leftmost digit) and the leaf (such as the rightmost digit). |
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| Uses bars of equal width to show frequencies of categories of qualitative data. The vertical scale represents frequencies or relative frequencies. The horizontal scale identifies the different categories of qualitative data. |
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Definition
| A bar graph for qualitative data, with the added stipulation that the bars are arranged in descending order according to frequencies. The vertical scale in a Pareto chart represents frequencies or relative frequencies. The horizontal scale identifies the different categories of qualitative data. The bars decrease in height from left to right. |
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Definition
| Depicts qualitative data as slices of a circle, in which the size of each slice is proportional to the frequency count for the category. |
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Definition
| A plot of paired (x, y) quantitative data with a horizontal x-axis and a vertical y-axis. The horizontal axis is used for the first (x) variable, and the vertical axis is used for the second variable. The pattern of the plotted points is often helpful in determining whether there is a relationship between the two variables. |
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Definition
| A graph of time-series data, which are quantitative data that have been collected in different points in time. |
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Definition
68% of all data lie within 1 std. deviation of the center
95% of all data lie within 2 std. deviations of the center
99.7% of all data lie within 3 std. deviations of the center |
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Term
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Definition
| max value - min. value = range |
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| Maximum & Minimum Usual Values |
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Definition
| A value is unusual if it lies more than 2 std. deviations from the mean in either direction. |
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| Coefficient of Variation (CV) |
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Definition
Expressed as a percentage. Describes the std. deviation relative to the mean. Small number means it varies very little. Large number mean it varies a lot.
CV = std. deviation / mean |
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Definition
The number of standard deviations that a given value, x, is above or below the mean.
(x - mean) / S.D. |
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Definition
| As a procedure is repeated again and again, the relative frequency probability of an event tends to approach the actual probability. |
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