Time Series Analysis

When to use

• Building a forecast for operational planning (staffing, inventory, infrastructure capacity)
• Identifying whether a trend is genuine or driven by seasonality
• Detecting anomalies in a metric stream (traffic spikes, revenue dips, error rate surges)
• Providing a "what would have happened" baseline for measuring initiative impact
• Presenting year-over-year growth in a way that accounts for seasonal patterns

Process

1. Load and inspect the time series, confirm regular intervals (fill gaps if needed), check for obvious data quality issues (negative values, zeros in non-zero series), and identify the natural granularity (daily, weekly, monthly).
2. Test for stationarity, run an ADF test. If non-stationary (trend or seasonality present), note this, it informs decomposition and model choice rather than blocking analysis. See references/ts_patterns_guide.md.
3. Decompose into components, separate the time series into trend, seasonal, and residual using additive or multiplicative decomposition. Measure the strength of each component (0, 1). Strong seasonality (>0.6) means raw values are misleading without seasonal adjustment.
4. Detect anomalies, flag points more than 3 standard deviations from the rolling median. Investigate the top 5 anomalies against the event log (product releases, campaigns, incidents). Use scripts/ts_analyzer.py --detect-anomalies.
5. Fit a forecast model, fit an ARIMA model (or simpler moving average if data is short). Validate on a held-out 20% test set and report MAPE. Generate point estimates and 95% confidence intervals for the forecast horizon.
6. Produce the analysis report, summarise trend direction and strength, seasonal patterns and their business implications, anomaly findings, and the forecast with uncertainty. Use assets/ts_report_template.md.