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Biostatistics for Animal Science

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6 <strong>Biostatistics</strong> <strong>for</strong> <strong>Animal</strong> <strong>Science</strong><br />

1.4 Numerical Methods <strong>for</strong> Presenting Data<br />

Numerical methods <strong>for</strong> presenting data are often called descriptive statistics. They include:<br />

a) measures of central tendency; b) measures of variability ; c) measures of the shape of a<br />

distribution; and d) measures of relative standing.<br />

a) measures of<br />

central tendency<br />

b) measures of<br />

variability<br />

Descriptive statistics<br />

c) measures of the<br />

shape of a<br />

distribution<br />

d) measures of<br />

relative position<br />

- arithmetic mean - range - skewness - percentiles<br />

- median - variance - kurtosis - z-values<br />

- mode - standard deviation<br />

- coefficient of<br />

variation<br />

Be<strong>for</strong>e descriptive statistics are explained in detail, it is useful to explain a system of<br />

symbolic notation that is used not only in descriptive statistics, but in statistics in general.<br />

This includes the symbols <strong>for</strong> the sum, sum of squares and sum of products.<br />

1.4.1 Symbolic Notation<br />

The Greek letter Σ (sigma) is used as a symbol <strong>for</strong> summation, and yi <strong>for</strong> the value <strong>for</strong><br />

observation i.<br />

The sum of n numbers y1, y2,…, yn can be expressed:<br />

Σi yi = y1 + y2 +.....+ yn<br />

The sum of squares of n numbers y1, y2,…, yn is:<br />

Σi y 2 i = y 2 1 + y 2 2 +.....+ y 2 n<br />

The sum of products of two sets of n numbers (x1, x2,…, xn) and (y1, y2,…, yn):<br />

Σi xiyi = x1y1 + x2y2 +.....+ xnyn<br />

Example: Consider a set of three numbers: 1, 3 and 6. The numbers are symbolized by:<br />

y1 = 1, y2 = 3 and y3 = 6.<br />

The sum and sum of squares of those numbers are:<br />

Σi yi = 1 + 3 + 6 = 10

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