Historical Cost Analyzer for Construction

Overview

Analyze historical construction cost data for benchmarking, escalation tracking, and estimating calibration. Compare similar projects, identify cost drivers, and improve future estimates.

Business Case

Historical cost analysis enables:

• Benchmarking: Compare current estimates to past projects
• Calibration: Improve estimating accuracy using actual data
• Trends: Track cost escalation and market changes
• Risk Assessment: Identify cost drivers and overrun patterns

Technical Implementation

python
from dataclasses import dataclass, field
from typing import List, Dict, Any, Optional, Tuple
import pandas as pd
import numpy as np
from datetime import datetime
from scipy import stats

@dataclass
class CostBenchmark:
    metric_name: str
    value: float
    unit: str
    percentile_25: float
    percentile_50: float
    percentile_75: float
    sample_size: int
    project_types: List[str]

@dataclass
class EscalationAnalysis:
    from_year: int
    to_year: int
    annual_rate: float
    total_change: float
    category: str
    confidence: float

@dataclass
class CostDriver:
    factor: str
    impact_percentage: float
    correlation: float
    description: str

class HistoricalCostAnalyzer:
    """Analyze historical construction costs."""

    # RSMeans City Cost Indexes (sample - would be loaded from database)
    LOCATION_FACTORS = {
        'New York': 1.32, 'San Francisco': 1.28, 'Los Angeles': 1.15,
        'Chicago': 1.12, 'Houston': 0.92, 'Dallas': 0.89,
        'Phoenix': 0.93, 'Atlanta': 0.91, 'Denver': 1.02,
        'Seattle': 1.08, 'National Average': 1.00
    }

    # Historical cost indices by year
    COST_INDICES = {
        2015: 100.0, 2016: 102.1, 2017: 105.3, 2018: 109.2,
        2019: 112.5, 2020: 114.8, 2021: 121.4, 2022: 135.6,
        2023: 142.3, 2024: 148.7, 2025: 154.2, 2026: 160.0
    }

    def __init__(self, historical_data: pd.DataFrame = None):
        self.data = historical_data
        self.benchmarks: Dict[str, CostBenchmark] = {}

    def load_data(self, data: pd.DataFrame):
        """Load historical project data."""
        self.data = data.copy()

        # Normalize data
        if 'completion_year' not in self.data.columns and 'completion_date' in self.data.columns:
            self.data['completion_year'] = pd.to_datetime(self.data['completion_date']).dt.year

        # Calculate key metrics
        if 'gross_area' in self.data.columns and 'final_cost' in self.data.columns:
            self.data['cost_per_sf'] = self.data['final_cost'] / self.data['gross_area']

        if 'original_estimate' in self.data.columns and 'final_cost' in self.data.columns:
            self.data['overrun_pct'] = ((self.data['final_cost'] - self.data['original_estimate'])
                                         / self.data['original_estimate'] * 100)

    def normalize_to_year(self, costs: pd.Series, from_years: pd.Series,
                          to_year: int = 2026) -> pd.Series:
        """Normalize costs to a common year using cost indices."""
        normalized = costs.copy()

        for i, (cost, year) in enumerate(zip(costs, from_years)):
            if pd.notna(cost) and pd.notna(year):
                year = int(year)
                if year in self.COST_INDICES and to_year in self.COST_INDICES:
                    factor = self.COST_INDICES[to_year] / self.COST_INDICES[year]
                    normalized.iloc[i] = cost * factor

        return normalized

    def normalize_to_location(self, costs: pd.Series, locations: pd.Series,
                               to_location: str = 'National Average') -> pd.Series:
        """Normalize costs to a common location."""
        normalized = costs.copy()
        to_factor = self.LOCATION_FACTORS.get(to_location, 1.0)

        for i, (cost, loc) in enumerate(zip(costs, locations)):
            if pd.notna(cost) and loc in self.LOCATION_FACTORS:
                from_factor = self.LOCATION_FACTORS[loc]
                normalized.iloc[i] = cost * (to_factor / from_factor)

        return normalized

    def calculate_benchmarks(self, project_type: str = None,
                              year_range: Tuple[int, int] = None) -> Dict[str, CostBenchmark]:
        """Calculate cost benchmarks from historical data."""
        df = self.data.copy()

        # Filter by project type
        if project_type and 'project_type' in df.columns:
            df = df[df['project_type'] == project_type]

        # Filter by year range
        if year_range and 'completion_year' in df.columns:
            df = df[(df['completion_year'] >= year_range[0]) &
                    (df['completion_year'] <= year_range[1])]

        benchmarks = {}

        # Cost per SF
        if 'cost_per_sf' in df.columns:
            values = df['cost_per_sf'].dropna()
            if len(values) > 0:
                benchmarks['cost_per_sf'] = CostBenchmark(
                    metric_name='Cost per SF',
                    value=values.median(),
                    unit='$/SF',
                    percentile_25=values.quantile(0.25),
                    percentile_50=values.quantile(0.50),
                    percentile_75=values.quantile(0.75),
                    sample_size=len(values),
                    project_types=[project_type] if project_type else df['project_type'].unique().tolist()
                )

        # Overrun percentage
        if 'overrun_pct' in df.columns:
            values = df['overrun_pct'].dropna()
            if len(values) > 0:
                benchmarks['overrun_pct'] = CostBenchmark(
                    metric_name='Cost Overrun',
                    value=values.median(),
                    unit='%',
                    percentile_25=values.quantile(0.25),
                    percentile_50=values.quantile(0.50),
                    percentile_75=values.quantile(0.75),
                    sample_size=len(values),
                    project_types=[project_type] if project_type else df['project_type'].unique().tolist()
                )

        self.benchmarks.update(benchmarks)
        return benchmarks

    def calculate_escalation(self, category: str = 'overall',
                              from_year: int = 2020,
                              to_year: int = 2026) -> EscalationAnalysis:
        """Calculate cost escalation between years."""
        if from_year in self.COST_INDICES and to_year in self.COST_INDICES:
            from_index = self.COST_INDICES[from_year]
            to_index = self.COST_INDICES[to_year]

            total_change = (to_index - from_index) / from_index
            years = to_year - from_year
            annual_rate = (to_index / from_index) ** (1 / years) - 1 if years > 0 else 0

            return EscalationAnalysis(
                from_year=from_year,
                to_year=to_year,
                annual_rate=annual_rate,
                total_change=total_change,
                category=category,
                confidence=0.95
            )

        return None

    def identify_cost_drivers(self, target_col: str = 'cost_per_sf') -> List[CostDriver]:
        """Identify factors that drive costs."""
        if self.data is None or target_col not in self.data.columns:
            return []

        drivers = []
        target = self.data[target_col].dropna()

        # Analyze numeric columns
        numeric_cols = self.data.select_dtypes(include=[np.number]).columns
        exclude = [target_col, 'final_cost', 'original_estimate']

        for col in numeric_cols:
            if col not in exclude:
                valid_mask = self.data[col].notna() & self.data[target_col].notna()
                if valid_mask.sum() > 10:
                    corr, p_value = stats.pearsonr(
                        self.data.loc[valid_mask, col],
                        self.data.loc[valid_mask, target_col]
                    )

                    if abs(corr) > 0.3 and p_value < 0.05:
                        impact = corr * self.data[col].std() / target.std() * 100

                        drivers.append(CostDriver(
                            factor=col,
                            impact_percentage=abs(impact),
                            correlation=corr,
                            description=f"{'Positive' if corr > 0 else 'Negative'} correlation with {target_col}"
                        ))

        # Analyze categorical columns
        categorical_cols = self.data.select_dtypes(include=['object', 'category']).columns

        for col in categorical_cols:
            if col not in ['project_id', 'project_name']:
                groups = self.data.groupby(col)[target_col].mean()
                if len(groups) > 1:
                    variance = groups.var()
                    overall_var = target.var()

                    if variance / overall_var > 0.1:
                        drivers.append(CostDriver(
                            factor=col,
                            impact_percentage=variance / overall_var * 100,
                            correlation=0,
                            description=f"Categorical factor with significant cost variation"
                        ))

        return sorted(drivers, key=lambda x: -x.impact_percentage)

    def compare_to_benchmark(self, estimate: Dict, project_type: str = None) -> Dict:
        """Compare an estimate to historical benchmarks."""
        if project_type:
            self.calculate_benchmarks(project_type)

        comparison = {}

        # Cost per SF comparison
        if 'cost_per_sf' in estimate and 'cost_per_sf' in self.benchmarks:
            benchmark = self.benchmarks['cost_per_sf']
            value = estimate['cost_per_sf']

            percentile = stats.percentileofscore(
                self.data['cost_per_sf'].dropna(), value
            )

            comparison['cost_per_sf'] = {
                'estimate': value,
                'benchmark_median': benchmark.value,
                'benchmark_range': (benchmark.percentile_25, benchmark.percentile_75),
                'percentile': percentile,
                'status': 'within_range' if benchmark.percentile_25 <= value <= benchmark.percentile_75 else 'outside_range'
            }

        return comparison

    def find_similar_projects(self, criteria: Dict, n: int = 10) -> pd.DataFrame:
        """Find similar historical projects."""
        df = self.data.copy()

        # Filter by criteria
        if 'project_type' in criteria:
            df = df[df['project_type'] == criteria['project_type']]

        if 'gross_area' in criteria:
            target = criteria['gross_area']
            tolerance = criteria.get('area_tolerance', 0.3)
            df = df[(df['gross_area'] >= target * (1 - tolerance)) &
                    (df['gross_area'] <= target * (1 + tolerance))]

        if 'location' in criteria and 'location' in df.columns:
            df = df[df['location'] == criteria['location']]

        if 'year_range' in criteria:
            df = df[(df['completion_year'] >= criteria['year_range'][0]) &
                    (df['completion_year'] <= criteria['year_range'][1])]

        # Sort by similarity (simple: by area difference)
        if 'gross_area' in criteria and 'gross_area' in df.columns:
            df['similarity'] = 1 - abs(df['gross_area'] - criteria['gross_area']) / criteria['gross_area']
            df = df.sort_values('similarity', ascending=False)

        return df.head(n)

    def analyze_overrun_patterns(self) -> Dict:
        """Analyze patterns in cost overruns."""
        if 'overrun_pct' not in self.data.columns:
            return {}

        analysis = {}

        # Overall statistics
        overruns = self.data['overrun_pct'].dropna()
        analysis['overall'] = {
            'mean': overruns.mean(),
            'median': overruns.median(),
            'std': overruns.std(),
            'projects_over_budget': (overruns > 0).sum(),
            'projects_under_budget': (overruns < 0).sum(),
            'pct_over_budget': (overruns > 0).mean() * 100
        }

        # By project type
        if 'project_type' in self.data.columns:
            by_type = self.data.groupby('project_type')['overrun_pct'].agg(['mean', 'std', 'count'])
            analysis['by_type'] = by_type.to_dict('index')

        # By size category
        if 'gross_area' in self.data.columns:
            self.data['size_category'] = pd.cut(
                self.data['gross_area'],
                bins=[0, 10000, 50000, 100000, np.inf],
                labels=['Small (<10k SF)', 'Medium (10-50k SF)', 'Large (50-100k SF)', 'Very Large (>100k SF)']
            )
            by_size = self.data.groupby('size_category')['overrun_pct'].agg(['mean', 'std', 'count'])
            analysis['by_size'] = by_size.to_dict('index')

        return analysis

    def generate_report(self, project_type: str = None) -> str:
        """Generate comprehensive cost analysis report."""
        lines = ["# Historical Cost Analysis Report", ""]
        lines.append(f"**Generated:** {datetime.now().strftime('%Y-%m-%d')}")
        lines.append(f"**Projects Analyzed:** {len(self.data):,}")
        if project_type:
            lines.append(f"**Project Type:** {project_type}")
        lines.append("")

        # Benchmarks
        benchmarks = self.calculate_benchmarks(project_type)
        if benchmarks:
            lines.append("## Cost Benchmarks")
            for name, bm in benchmarks.items():
                lines.append(f"\n### {bm.metric_name}")
                lines.append(f"- **Median:** {bm.value:.2f} {bm.unit}")
                lines.append(f"- **25th Percentile:** {bm.percentile_25:.2f} {bm.unit}")
                lines.append(f"- **75th Percentile:** {bm.percentile_75:.2f} {bm.unit}")
                lines.append(f"- **Sample Size:** {bm.sample_size}")

        # Escalation
        lines.append("\n## Cost Escalation")
        esc = self.calculate_escalation(from_year=2020, to_year=2026)
        if esc:
            lines.append(f"- **Period:** {esc.from_year} to {esc.to_year}")
            lines.append(f"- **Annual Rate:** {esc.annual_rate:.1%}")
            lines.append(f"- **Total Change:** {esc.total_change:.1%}")

        # Cost Drivers
        drivers = self.identify_cost_drivers()
        if drivers:
            lines.append("\n## Key Cost Drivers")
            for driver in drivers[:5]:
                lines.append(f"- **{driver.factor}:** {driver.impact_percentage:.1f}% impact (r={driver.correlation:.2f})")

        # Overrun Analysis
        overrun_analysis = self.analyze_overrun_patterns()
        if 'overall' in overrun_analysis:
            lines.append("\n## Overrun Analysis")
            overall = overrun_analysis['overall']
            lines.append(f"- **Average Overrun:** {overall['mean']:.1f}%")
            lines.append(f"- **Projects Over Budget:** {overall['pct_over_budget']:.1f}%")

        return "\n".join(lines)

Quick Start

python
import pandas as pd

# Load historical data
historical = pd.read_excel("historical_projects.xlsx")

# Initialize analyzer
analyzer = HistoricalCostAnalyzer()
analyzer.load_data(historical)

# Calculate benchmarks for office buildings
benchmarks = analyzer.calculate_benchmarks(project_type='Office')
print(f"Office median cost: ${benchmarks['cost_per_sf'].value:.2f}/SF")

# Calculate escalation
escalation = analyzer.calculate_escalation(from_year=2020, to_year=2026)
print(f"Annual escalation: {escalation.annual_rate:.1%}")

# Find similar projects
similar = analyzer.find_similar_projects({
    'project_type': 'Office',
    'gross_area': 50000,
    'year_range': (2020, 2025)
})
print(f"Found {len(similar)} similar projects")

# Compare estimate to benchmark
comparison = analyzer.compare_to_benchmark({'cost_per_sf': 250}, 'Office')
print(f"Estimate percentile: {comparison['cost_per_sf']['percentile']:.0f}th")

# Generate report
report = analyzer.generate_report('Office')
print(report)

Dependencies

bash
pip install pandas numpy scipy