When data are described by a measure of central tendency (mean,
median, or mode), all the scores are summarized by a single value.
Reports of central tendency are commonly supplemented and complemented
by including a measure of dispersion. The measures of dispersion you
have just seen differ in ways that will help determine which one is
most useful in a particular situation.Range Of all the measures of
dispersion, the range is the easiest to determine. It is commonly used
as a preliminary indicator of dispersion. However, because it takes
into account only the scores that lie at the two extremes, it is of
limited use.
Quartile Scores are based on more information than the range and,
unlike the range, are not affected by outliers. However, they are only
infrequently used to describe dispersion because they are not as easy
to calculate as the range and they do not have the mathematical
properties that make them so useful as standard deviation and
variance.
The standard deviation and variance are more complete measures of
dispersion which take into account every score in a distribution. The
other measures of dispersion we have discussed are based on
considerably less information. However, because variance relies on the
squared differences of scores from the mean, a single outlier has
greater impact on the size of the variance than does a single score
near the mean. Some statisticians view this property as a shortcoming
of variance as a measure of dispersion, especially when there is
reason to doubt the reliability of some of the extreme scores. For
example, a researcher might believe that a person who reports watching
television an average of 24 hours per day may have misunderstood the
question. Just one such extreme score might result in an appreciably
larger standard deviation, especially if the sample is small.
Fortunately, since all scores are used in the calculation of variance,
the many non-extreme scores (those closer to the mean) will tend to
offset the misleading impact of any extreme scores.
The standard deviation and variance are the most commonly used
measures of dispersion in the social sciences because:
Both take into account the precise difference between each score and
the mean. Consequently, these measures are based on a maximum amount
of information.
The standard deviation is the baseline for defining the concept of
standardized score or "z-score".
Variance in a set of scores on some dependent variable is a baseline
for measuring the correlation between two or more variables (the
degree to which they are related).
----
On Mon, Jun 4, 2012 at 5:25 PM, +!~Whats myfault?+!~
<
whatsmyfault1@gmail.com> wrote:
> gdb .. open hone tow dein abi..
>
> On Mon, Jun 4, 2012 at 5:01 PM, Cooldoud Hina <
cooldoudhina@gmail.com> wrote:
>> plz sta301 k gdb ka solution send krdo
>>
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