STATISTICS (reliability, validity, data)

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STATISTICS(reliability, validity, data)
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What's the point of research??

• Research is important for many reasons not least
  for the following
• Research allows you knowledge, without knowledge,
  based upon research, you just have an argument,
  or an opinionits all assumptions!!!

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RELIABILITY

• If a bus arrived every morning at 8.30am.you
  would keep using this service wouldnt you?
• Conversely if the bus service was erraticI.e.
  You couldnt estimate when it arrived..you would
  not use it, because it wasn't consistent.
• Thus reliability is a measure of consistency

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RELIABILITY

• There are several ways you could test the
  reliability of a measurement each come with their
  own limitations!!
• Split half reliability.Complete a correlation
  between the first half of the sample and the
  second half.
• Test retest reliability. Test the participants
  once, calculate a correlation, then retest the
  participants again. The higher the co-efficient,
  the higher the reliability
• Odd even reliability. Compare the correlation
  between the odd numbers and even numbers.

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VALIDITY..

• There are two main types of validity
• External The extent to which the results can
  be generalised to the population and other
  settings.
• Internal Can the results be attributed to the
  manipulation of the IV or were there other
  factors that effected the results.

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Descriptive Statistics.

• Psychologists summarise their data numerically
  through
• Levels of data
• Measures of Central tendency
• Measures of Dispersion.

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Levels of data

• Nominal data Ordinal data interval/ratio

Interval data is continuous data where
differences are interpretable, but where there
is no "natural" zero.
categorical data where the order of the
categories is arbitrary
categorical data Where there is a logical
ordering
Likert scale 1 agree, 2disagree
Ethnic monitoring 1 Black 2 White.
temperature
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Measures of Dispersion.

• Range The difference between the smallest and
  the largest value, plus 1.
• E.g. 4 7 7 8 9 (9-4)1 Range of 6.
• Standard Deviation The average amount all scores
  deviate from the mean.
• (Next 2 slides give an example of how to
  calculate the SD.)

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Standard deviation.

• The standard deviation is the distribution of
  scores among the data and also happen to be the
  most frequent scores.
• The purpose of calculating the SD is to discover
  how many of the scores deviate from the average
  (think of the curve of normal distribution!!)
• In order to decide whether results gained from
  research are trustworthy we take into account the
  validity of the results.

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Standard Deviation explained
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Step 1 Workout the mean of the scores by adding
all values and divide by number   Total
50/510.thus the mean is 10.   Step 2 Minus the
mean from the score (doesnt matter if you get
Minus numbers as the mean of these numbers are
squared to get rid of the minus).   Step 3 Add
the squared values to get a total.   Mean of the
total (40 8, this is the variance of the square
root of variance.)   Step 4 the square root of
the variance is calculated and this gives you the
standard deviation