# Important terms in data analysis

Dependent variables

In EthoVision XT, a Dependent variable is a variable that quantifies the behavior of a subject or marks an event occurred in a trial.

▪example 1 To quantify locomotor activity, choose Distance moved, or Velocity, or Movement as Dependent variables.

▪example 2 To calculate how many food pellets were dropped by a pellet dispenser, choose Hardware continuous as a Dependent variable.

Dependent variables are calculated for each sample of the track, when data are available. The table below shows the Distance moved calculated for a few samples. X and Y are the coordinates of the center of the subject's body. Note that distance moved is not calculated at time = 0, because there is no previous sample to use as a reference.

Time | X | Y | Distance moved
0 | -8.7393 | -26.1678 | –
0.08 | -6.8267 | -26.9699 | 2.0740
0.16 | -4.7220 | -27.0748 | 2.1074
0.24 | -3.2380 | -26.6227 | 1.5513

State dependent variables

Some dependent variables are state variables, that is, they have discrete values. For example, In zone with values 1 (in zone) and 0 (not in zone). The following table shows the In zone variable calculated for the zone A and for a few samples. When the animal’s body point is found within zone A, then In zone=1, otherwise In zone=0. In the example below, the subject's center point enters the zone at 0.16 s.

Time | X | Y | In zone
0 | -8.7393 | -26.1678 | 0
0.08 | -6.8267 | -26.9699 | 0
0.16 | -4.7220 | -27.0748 | 1
0.24 | -3.2380 | -26.6227 | 1

Statistics

In EthoVision XT, Statistics are descriptive statistics of the per-sample values of a Dependent variable.

▪example 1 To quantify locomotor activity, choose the Total statistic for the dependent variable Distance moved. Choose the Mean statistic for the dependent variable Velocity.

The Total distance moved is the sum of the per-sample values of distance. In the example of the table above, the total is 5.73 cm.

▪example 2 To calculate the time spent in zone, choose the Total statistic for the dependent variable In zone.

Trial statistics vs. Group statistics

For each dependent variable you can specify two types of statistics:

▪Trial Statistics

Statistics calculated per trial.

example Your experiment contains 100 trials of one animal in one arena. Choose Total as a Trial Statistic for the dependent variable Distance moved. You obtain 100 values of Total Distance moved.

▪Group Statistics

Summary statistics of the Trial Statistics, calculated over all the trials specified in the data profile, or in a group.

example You have defined two groups of tracks, Treated and Saline, and you want to calculate the Mean and Standard deviation of Distance moved and other variables per group.

In the example above with the 100 trials, with Group Statistics you would obtain the average and standard deviation of the 100 values of distance moved.