Standard transforms

This page explains the built-in functions you can choose from the Transform dialog. Other pages explain how to use the special transforms for pharmacology and biochemistry and how to enter your own transforms.

Built-in transforms

Choose from one of these functions for transforming Y values (analogous functions are available for X):

Function

Comments

Y= Y * K
Y = Y + K
Y = Y – K
Y = Y / K
Y = Y squared
Y = Y ^ K
Y = log(Y)
Y = -1*log(Y)
Y = ln(Y)
Y = 10 ^ Y
Y = exp(Y)
Y = 1/Y
Y = sqrt(Y)
Y = logit(y)
Y = probit(Y)
Y = rank(Y)
Y = zscore(Y)
Y = sin(Y)
Y = cos(Y)
Y = tan(Y)
Y = arcsin(Y)
Y = ABS(Y)
Y = Y + Random
Y = X / Y
Y = Y / X
Y = Y – X
Y = Y + X
Y = Y * X
Y = X – Y

Enter K in the box provided.
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Enter K in the box provided.
Log base 10

Natural logarithm (base e)
Ten to the Yth power (inverse of log).
eY (inverse of ln)

Square root.
ln(Y/1-Y)
Y must be between 0.0 and 1.0
Column rank. Smallest Y value gets rank of 1.
Number of SDs from the column mean.
Y is in radians.
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Result is in radians.
Absolute value.
Gaussian. Mean=0. SD=K (you enter).

Many of the functions include the variable “K”. Enter a value for K on the dialog. When transforming Y values, you can enter one value of K for all data sets or a separate value of K for each data set. To enter different K values for each data set, choose a data set, enter K, choose another data set, enter its K, and so on.

Rather than entering the value of K, you can hook an analysis or info constant.

Interchanging X and Y

When you choose a standard function, you can choose to interchange X and Y values and also choose transforms of X or Y or both.

Some notes on interchanging X and Y values:

•	Prism can interchange data on tables with more than one data set (more than one Y column), even though the results sheet has only a single X column. It does this by creating additional rows. The results will be staggered down the page with only one data set in any particular row.

•	If you entered replicate Y values (or mean with SD or SEM) Prism interchanges X and Y by putting the mean Y value into the X column. Information about the scatter of Y is ignored.

•	If you selected X or Y transforms (in addition to interchanging), Prism applies the transform to the data after interchanging X and Y. This means that the X transform is applied to data that were originally in the Y column, and the Y transform is applied to data originally in the X column.

Transforming error values

If you entered replicate Y values, Prism can transform each replicate or the mean of the replicates.

If you entered data as mean, SD (or SEM), and N, Prism tries to transform the error bar as well as the mean. When a transform is intrinsically asymmetrical (i. e. logarithms), it is mathematically impossible to transform a SD and end up with a SD. You have two choices. You may either transform the mean only or erase the error bars. Or you may convert the error bars to 95% confidence intervals, and then transform both ends of the confidence interval. The resulting 95% CI will be asymmetrical.