In machine learning, misclassification rate is a metric that tells us the percentage of observations that were incorrectly predicted by some classification model.
It is calculated as:
Misclassification Rate = # incorrect predictions / # total predictions
The value for misclassification rate can range from 0 to 1 where:
- 0 represents a model that had zero incorrect predictions.
- 1 represents a model that had completely incorrect predictions.
The lower the value for the misclassification rate, the better a classification model is able to predict the outcomes of the response variable.
The following example show how to calculate misclassification rate for a logistic regression model in practice.
Example: Calculating Misclassification Rate for a Logistic Regression Model
Suppose we use a logistic regression model to predict whether or not 400 different college basketball players get drafted into the NBA.
The following confusion matrix summarizes the predictions made by the model:
Here is how to calculate the misclassification rate for the model:
- Misclassification Rate = # incorrect predictions / # total predictions
- Misclassification Rate = (false positive + false negative) / (total predictions)
- Misclassification Rate = (70 + 40) / (400)
- Misclassification Rate = 0.275
The misclassification rate for this model is 0.275 or 27.5%.
This means the model incorrectly predicted the outcome for 27.5% of the players.
The opposite of misclassification rate would be accuracy, which is calculated as:
- Accuracy = 1 – Misclassification rate
- Accuracy = 1 – 0.275
- Accuracy = 0.725
This means the model correctly predicted the outcome for 72.5% of the players.
Pros & Cons of Misclassification Rate
Misclassification rate offers the following pros:
- It’s easy to interpret. A misclassification rate of 10% means a model made an incorrect prediction for 10% of the total observations.
- It’s easy to calculate. A misclassification rate is calculated as the number of total incorrect predictions divided by the total number of predictions.
However, misclassification rate has the following con:
- It doesn’t take into account how the data is distributed. For example, suppose 90% of all players do not get drafted into the NBA. If we have a model that simply predicts every player to not get drafted, the model would have a misclassification rate of just 10%. This seems low, but, but the model is actually unable to correctly predict any player who gets drafted.
In practice, we often calculate the misclassification rate of a model along with other metrics like:
- Sensitivity: The “true positive rate” – the percentage of positive outcomes the model is able to detect.
- Specificity: The “true negative rate” – the percentage of negative outcomes the model is able to detect.
- F1 Score: A metric that tells us the accuracy of a model, relative to how the data is distributed.
By calculating the value for each of these metrics, we can gain a full understanding of how well the model is able to make predictions.
The following tutorials provide additional information about common machine learning concepts: