Population Populations are the core of primitive of the Semilattice API.

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What is a population?

A population is a model that represents a specific group of people in reality. When you call the API with a population_id, you’re telling Semilattice which group to simulate.

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Target population

Population models have a reality_target metadata field which describes the group of people in reality the model is intended to represent. When choosing a population model, select the one that best matches your target audience or user profile.

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Populations range from broad user profiles to highly specific niches.

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Seed data

Populations are built using tabular question-answer data (such as survey data) from the target audience. This seed data determines:
  • Prediction accuracy: How well the model predicts the target audience
  • Subject expertise: What topics the population can predict accurately

Seed data define population models

Learn more about how populations are created in the seed data section.

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Accuracy evaluation

Every population model, once tested, has evaluation metrics that help you understand prediction accuracy:

Accuracy metrics help assess prediction confidence

These metrics appear in API responses and help you:
  • Choose the right population for your use case
  • Set appropriate confidence levels for your predictions
  • Understand the reliability of specific results
Learn more about these metrics and how to interpret them in the Accuracy Evaluation guide.

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Simulation engine

Each population uses a specific version of Semilattice’s simulation engine. This ensures:
  • Consistency: All predictions use the same model version
  • Accuracy: Evaluation metrics reflect real prediction performance
  • Reliability: Results are reproducible

Populations use consistent simulation engines

The simulation_engine field in API responses tells you which engine was used. All public population models use the answers-1 simulation engine.

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Public vs. custom populations

When making API calls, you can access:
  • Public populations: Available to all users with valid API keys
  • Custom populations: Only accessible to the owner’s API key

API access depends on population privacy settings

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Finding population IDs

To use a population in your API calls, you need its ID. Navigate to the Populations page in your dashboard and select a population model to use. Copy the ID from the population’s metadata or from the address bar.

Click to copy the population model's ID