Back to catalog

Westinghouse · Portable generator · Model WGen9500DFc

WGen9500DFc

WGen9500DFc - Dual Fuel with CO Sensor

9,500W running12,500W peakDual fuel: gasoline + propane457cc · OHV 4 Stroke
Check retailer availability Official listed price $1,399.00
WGen9500DFc - Dual Fuel with CO Sensor
Official product image · Westinghouse

Product decision summary

Researched by · reviewed under the FMG editorial standard · Sep 15, 2026

Trace the evidence · not a hands-on review

Bottom line

Competitive in its class for whole-home backup planning & transfer-switch applications.

Best for: Whole-home backup planning & Transfer-switch applications

Running output

9,500W

Fuel / power

Dual fuel: gasoline + propane

Weight

212 lb

Strongest reasons

  • The Westinghouse WGen9500DFc Dual Fuel Portable Generator with CO Sensor produces up to 12,500 peak watts and 9,500 running watts, the WGen9500DFc is a dual fuel generator that operates on gasoline or propane (LPG).
  • Peak output is higher than 64% of its class.
  • Published sound level is quieter than 63% of its class.

Know before buying

At 212 lb, this is a wheeled or placed unit—not a carry-style generator.

Best current buying route

$1,399

MSRP at Westinghouse / retailer network

Ranked first across 2 verified sellers using listed price, stock status, freshness, and published terms. Shipping is not yet comparable. Confirm price, stock, shipping, and the exact model on the seller’s site.

Check price & availability

Affiliate links may earn us a commission at no added cost to you. Disclosure

Never run a fuel-burning generator in a home, garage, shed, or other enclosed or partly enclosed space.

Price intelligence Evidence ledger Accessories & manuals

The numbers that drive the decision.

Published values stay labeled, and every usable metric includes class context. Missing data is shown instead of estimated.

Open complete specifications
SpecificationThis model
Running output9,500WHigher than 62% of its class
Peak / starting output12,500WHigher than 64% of its class
Published runtime12 hrLonger than 62% of its class
Product weight212 lbLighter than 58% of its class
Published sound level74 dBAQuieter than 63% of its class
Fuel / power sourceDual fuel: gasoline + propanePortable generator
Best current price$1,399MSRP at Westinghouse / retailer network

Class comparisons use 144 high output portable generators. Runtime figures can use different loads, fuels, or test conditions; confirm the model manual before planning fuel or battery duration.

Product gallery & complete specifications Official imagery, full spec tables, use cases, and source linksView details

Output, fuel flexibility, portability, and protection.

01 · Output by fuel

12,500W maximum peak output

Gasoline9,500W / 12,500W
Propane8,500W / 11,200W

Bars compare Westinghouse's factory-published running and peak output for each supported fuel.

02 · Fuel & runtime

Dual fuel: gasoline + propane

457cc · OHV 4 Stroke

Capacity

6.6 gal. (25 L)

Runtime

Gasoline Run Time @ 25%: 12 hrs.; Gasoline Run Time @ 50%: 8 hrs.; Propane Run Time @ 50%: 7 hrs.

03 · Size & ownership

212.1 lb. (95.7 kg)

Dry or listed weight

27.2L x 26.1W x 26.5H in.

Product dimensions

Official listed price
$1,399.00
Purchase channel
Westinghouse retailer network
04 · Controls & protection

Starting

Remote and push-button electric start with recoil backup

Voltage

120/240V

Transfer switch

Factory-listed ready

CO shutdown

Published sensor

The complete current official image set for WGen9500DFc includes product views, control-panel diagrams, feature comparisons, and lifestyle graphics where Westinghouse publishes them.

WGen9500DFc official Westinghouse product image 1
Published by Westinghouse · image 1 of 13
WGen9500DFc official Westinghouse product image 2
Published by Westinghouse · image 2 of 13
WGen9500DFc official Westinghouse product image 3
Published by Westinghouse · image 3 of 13
WGen9500DFc official Westinghouse product image 4
Published by Westinghouse · image 4 of 13
WGen9500DFc official Westinghouse product image 5
Published by Westinghouse · image 5 of 13
WGen9500DFc official Westinghouse product image 6
Published by Westinghouse · image 6 of 13
WGen9500DFc official Westinghouse product image 7
Published by Westinghouse · image 7 of 13
WGen9500DFc official Westinghouse product image 8
Published by Westinghouse · image 8 of 13
WGen9500DFc official Westinghouse product image 9
Published by Westinghouse · image 9 of 13
WGen9500DFc official Westinghouse product image 10
Published by Westinghouse · image 10 of 13
WGen9500DFc official Westinghouse product image 11
Published by Westinghouse · image 11 of 13
WGen9500DFc official Westinghouse product image 12
Published by Westinghouse · image 12 of 13
WGen9500DFc official Westinghouse product image 13
Published by Westinghouse · image 13 of 13

The complete factory data available for comparison.

These pages retain Westinghouse's detailed model-specific specification fields, including output, amperage, outlets, engine, runtime, oil, compliance, grounding, dimensions, weight, included equipment, and warranty information where published.

Combustion generators are for outdoor use only. Keep the generator at least 20 feet from occupied buildings with exhaust directed away from doors, windows, and vents.

Product overview

The Westinghouse WGen9500DFc Dual Fuel Portable Generator with CO Sensor produces up to 12,500 peak watts and 9,500 running watts, the WGen9500DFc is a dual fuel generator that operates on gasoline or propane (LPG).

Comparison summary

Gasoline output
9,500W running / 12,500W peak
Propane output
8,500W running / 11,200W peak
Fuel or energy source
Dual fuel: gasoline + propane
Starting system
Remote and push-button electric start with recoil backup
Dimensions
27.2L x 26.1W x 26.5H in.
Dry or listed weight
212.1 lb. (95.7 kg)
Price and availability
Official listed price: $1,399.00; check current retailer availability

Factory electrical specifications

Grounding System
Bonded Neutral
RV Ready
Yes
Transfer Switch Ready
Yes
GFCI Outlets
Yes
Outlet Covers
Yes
AC Frequency
60 Hz
Outlets
2 Duplex 120V 5-20R. 1 120/240V L14-30R. 1 120/240V 14-50R. ST Switch
AC Voltage
120/240V
Gasoline Peak Amps
52A - 240V. 104A - 120V
Gasoline Running Amps
39.5A - 240V. 79A - 120V
Gasoline Running Watts
9500
Gasoline Peak Watts
12500
Total Harmonic Distortion
≤23%
Display Type
Digital Readout
Propane Peak Amps
47A - 240V. 93A - 120V
Propane Running Amps
35A - 240V. 71A - 120V
Propane Running Watts
8500
Propane Peak Watts
11200
ST Switch Ready
Yes

Factory engine, fuel & runtime specifications

Oil Capacity
37.2 oz. (1.1 qt.)
Engine Oil Type
10W30
Automatic Low Oil Shutdown
Yes
Engine Type
OHV 4 Stroke
Choke Type
Automatic
Engine Displacement
457cc
Gasoline Run Time @ 25%
12 hrs.
Fuel Gauge
Yes
Noise Level
74 dBA
Fuel Tank Capacity
6.6 gal. (25 L)
Gasoline Run Time @ 50%
8 hrs.
Propane Run Time @ 50%
7 hrs.

Factory safety, compliance & warranty specifications

Carbon Monoxide (CO) Sensor
Yes
Overload Protection
Yes
Battery Included
Yes
Warranty (Residential)
3 Year Limited
CARB Compliant
No
Warranty (Commercial)
1 Year Limited

Factory dimensions, portability & included equipment

Product Dimensions
27.2L x 26.1W x 26.5H in.
Shipping Weight
227.1 lb. (102.5 kg)
Packaging Dimensions
31L x 21.5W x 23H in.
Included Accessories
Oil Bottle, Oil Funnel, Spark Plug Wrench, Remote, Propane Regulator/Hose, Battery Float Charger
Dry Unit Weight
212.1 lb. (95.7 kg)
UPC
850011336663

Additional factory specifications

Starter Type
Electric, Remote, Recoil

Official feature details

Published Westinghouse feature

Perfect as a backup power source for larger homes or a dependable source of portable power

Power and operation

9,500 running watts, 12,500 peak watts (gasoline); 8500 running watts, 11,200 peak watts (propane)

Controls and convenience

Runs for up to 12 hours on a 6.6 gal. fuel tank with built-in fuel gauge; up to 7 hours on a 20 lb. propane tank

Connection capability

Powered by a heavy duty 457cc 4-Stroke OHV Westinghouse Engine constructed with a durable cast iron sleeve

Safety and protection

Push-Button Electric Start pairs with key fob and is backed by emergency recoil start

Portability detail

Dual fuel operation easily switches from gas to propane without shutting off unit

Ownership detail

Weighing 212.1 lb. with as low as 74 dBA operating volume

Additional manufacturer note

(2) GFCI 5-20R household duplex outlets, (1) Transfer Switch Ready L14-30R 120/240-Volt twist-lock, and (1) 120/240V 14-50R with rubber outlet covers

  • Whole-home backup planning
  • Transfer-switch applications
  • Large RV loads
  • Jobsites and events
  • 12,500W peak / 9,500W running
  • Dual fuel: gasoline + propane
  • Remote and push-button electric start with recoil backup
  • Carbon-monoxide sensor with automatic shutdown

Match it to the equipment you'll actually run.

Use the independent wattage calculator before buying.

Check my power plan

Compare the whole buying route.

The lowest sticker price is not always the best offer. We rank exact-model seller pages using price, stock, shipping, freshness, returns, and warranty details—then show what is still unknown.

Price and delivered cost

Shipping is included only when the seller publishes a usable amount.

Stock and freshness

Current, low-stock, preorder, and stale records are scored differently.

Purchase protections

Published return and warranty terms improve evidence confidence.

Affiliate-neutral ranking

Commission status is recorded but never adds ranking points.

Watch this model

Save it to your shortlist to retain the current price snapshot and turn price and safety watches on or off.

Best current buying route

Westinghouse WGen9500DFc

Review soon

MSRP

$1,399

at Westinghouse / retailer network · Verify stock

Verify offer

Seller options

2

1 with price

Offer rank

57/100

Relative to listed sellers

Data confidence

55%

4 open fields

Delivered totals

0/2

Shipping included

Ranked first across 2 verified sellers using listed price, stock status, freshness, and published terms. Shipping is not yet comparable.

Seller data checked Sep 15, 2026.

Shipping not yet verified.

Open fields: confirmed stock, delivered cost, return window, warranty term.

As an Amazon Associate we earn from qualifying purchases. Prices, local stock, shipping, taxes, installation, and seller terms can change. Confirm the exact model and final checkout total before buying. Affiliate disclosure.

Every verified exact-model destination.

Browse all priced models

2 exact-model seller destinations are ranked using price, availability, shipping, freshness, and published protections.

Westinghouse / retailer network

Best overallLowest listed
Review soon

$1,399

Final total at checkout

Availability
Verify stock
Shipping
Shipping not yet verified
Returns
Not verified
Warranty
Not verified
Verify seller

55% data confidence · checked Sep 15, 2026

Amazon

Affiliate
Review soon

Check current price

Total not available

Availability
Verify stock
Shipping
Shipping not yet verified
Returns
Not verified
Warranty
Not verified
Verify seller

30% data confidence · checked Sep 17, 2026

A durable record, starting with verified snapshots.

We preserve each dated seller observation instead of replacing the old number. Trends use the lowest verified listed price on each observation date—not an estimated market price.

Westinghouse / retailer network

$1,399 · Verify stock

Verify offer

What living with it looks like.

Ownership requires a safe fuel plan, hour-based engine service, correct storage, and confidence that parts and support are accessible.

Ownership rule

Use the exact Westinghouse WGen9500DFc manual for maintenance intervals, fluids, storage limits, and warranty requirements. Similar models are not interchangeable.

Published warranty

3 Year Limited

Commercial coverage: 1 Year Limited. Confirm eligibility and exclusions before purchase.

Service information

2 official resources

An owner or operator manual is linked below for exact service intervals.

Routine upkeep

37.2 oz. (1.1 qt.) · 10W30

Oil, filters, spark plug, fuel system, and starting battery needs vary by model and hours used.

Handling & storage

212 lb · Dual fuel: gasoline + propane

Plan a wheeled route, stable storage position, and help for steps or vehicle loading.

Practical care plan

From delivery to long-term readiness

  1. 1

    Day one

    Register and record the exact unit

    Save the receipt, serial number, seller, warranty terms, and model-specific manual before packaging is discarded.

  2. 2

    Before first load

    Complete setup and break-in correctly

    Add the specified oil, inspect the fuel system, position the generator outdoors, and follow the exact break-in and first-service instructions in the manual.

  3. 3

    Before every use

    Check the safety-critical basics

    Check oil level, leaks, cords, outlets, grounding instructions, CO-safe placement, and the transfer equipment needed for any building connection.

  4. 4

    By hours and season

    Log service and keep it outage-ready

    Track running hours and perform oil, filter, spark-plug, fuel-system, and starting-battery service at the intervals published for this exact model.

Before you buy

Five ownership questions to settle first

  • Confirm that 3 Year Limited applies to your seller, region, and intended use.
  • Open the official manual for WGen9500DFc and review setup, service intervals, warnings, and storage requirements.
  • Verify access to Westinghouse parts, authorized service, and a practical return path in your area.
  • Plan approved fuel storage, outdoor operating clearance, weather protection, and safe refueling.
  • Plan how the 212 lb unit will move over steps, gravel, and door thresholds.

See the proof behind the conclusion.

We separate sourced facts, reproducible calculations, editorial judgments, and missing evidence. That makes every important claim easier to inspect—and harder to overstate.

Published-data coverage

100%documented

8 of 8 relevant evidence fields are documented for this model.

Source-backed editorial analysis—not a hands-on or laboratory test.

Source record

3 traceable sources

Last reviewed Sep 15, 2026

Hands-on testing

Checking ledger…

No manufacturer data is presented as an independent test

Verified owners

Checking reports…

Percentages stay hidden until the sample qualifies

CPSC screening

No model-text match

39 generator recall records screened

100%

Documented fields

3

Traceable sources

4

Reproducible calculations

0

Open evidence gaps

Original calculation

Published surge reserve

3,000W

12,500W peak − 9,500W running

31.58% above rated running output. This is arithmetic headroom, not a promise that every motor load will start.

Original calculation

Rated power density

44.81 running W/lb

9,500W ÷ 212 lb

A catalog-derived portability ratio. It does not account for handles, wheels, shape, or how the weight feels in use.

Original calculation

Listed dollars per running kW

$147.26/kW

$1,399 ÷ 9.5 running kW

A point-in-time catalog value ratio. It excludes tax, shipping, accessories, fuel, service, and battery expansion costs.

Original calculation

Strongest class-relative spec

64th percentile

Peak output: 12,500W ranked within 144 high output portable generators

Higher than 64% of its class

Claim-by-claim evidence ledger

Evidence typeClaimBasisTrace
Published factSource-backed9,500W running and 12,500W peak output are recorded for this model.Model-specific output fields in the catalog.Official model source
Published factSource-backedDual fuel: gasoline + propane power and 212 lb product weight are recorded.Published configuration and dimensional data.Official model source
Original calculationReproduciblePublished surge reserve: 3,000W.12,500W peak − 9,500W runningCalculation standard
Original calculationReproducibleRated power density: 44.81 running W/lb.9,500W ÷ 212 lbCalculation standard
Original calculationReproducibleListed dollars per running kW: $147.26/kW.$1,399 ÷ 9.5 running kWCalculation standard
Editorial judgmentEditorialCompetitive in its class for whole-home backup planning & transfer-switch applications.Class score 64/100, declared best use, comparative specifications, and explicit buying cautions.Inspect the score
Editorial judgmentEditorialAt 212 lb, this is a wheeled or placed unit—not a carry-style generator.Editorial risk check based on product category, weight, output, price availability, and missing fields.Judgment standard

What this evidence cannot prove

  • No Find My Generator hands-on test, instrumented load test, teardown, or long-term ownership trial is claimed for this page.
  • Manufacturer specifications may use different fuels, loads, test distances, temperatures, or operating modes. Cross-brand comparisons inherit those differences.
  • The listed price is a dated snapshot and may not equal the current delivered price.

Editorial analysis for Westinghouse WGen9500DFc. Source record last verified Sep 15, 2026. Corrections can be submitted through the contact page with a model-specific source.

Accessories, manuals, and documents.

Start with the exact Westinghouse WGen9500DFc model or item number. Accessory families can look alike while using different connectors, electrical limits, engines, or mounting points.

Compatible accessories

Match by model and connection.

Verify exact fit

Generator power cord or inlet connection

Use a correctly rated cord or professionally selected inlet connection for the intended load.

Match voltage, amperage, blade pattern, and wire rating to L14-30R. Home connections require approved transfer equipment and qualified installation.
View official accessory options
Verify exact fit

Maintenance kit and service parts

Model-matched filters, spark plugs, batteries, oil supplies, and service parts support scheduled maintenance.

Match the complete WGen9500DFc model or item number and follow the maintenance table in its manual.
View official accessory options
Verify exact fit

Storage cover or approved running shelter

A fitted storage cover protects a cooled, stored generator. A running shelter must be designed for generator operation.

Never run a fuel-burning generator indoors or inside a storage cover. Follow the manual’s clearance and ventilation requirements.
View official accessory options

Manuals & PDFs

Official product materials.

Compatibility note: Links lead to manufacturer or official retailer resources. Confirm the full model or item number, connector type, voltage, amperage, and published compatibility list before buying. Installation involving a home panel, inlet, transfer switch, or fuel plumbing should be handled as required by local code.

Deeper analysis

Open the details you need

The key decision is above. These supporting scorecards, owner signals, and evidence notes stay out of the way until you want to inspect them.

Fit and score detailsSee the class benchmarks and personalize the fit score for your needs.

Find My Generator score

64/ 100

Competitive in its class

Compared with 144 high output portable generators in the current catalog.

Power63

Running and peak output versus the class

Endurance62

Longest published runtime figure

Portability58

Lower weight scores higher

Quietness63

Lower published dBA scores higher

Fuel flexibility90

Multiple fuel choices

Value56

Output or stored energy per listed dollar

See what each spec really means.

A number is more useful with context. Each row shows this model beside its class median and translates the difference into a percentile.

Running output

Higher than 62% of its class

This model · 9,500W
Median · 9,100W

Peak output

Higher than 64% of its class

This model · 12,500W
Median · 11,350W

Published runtime

Longer than 62% of its class

This model · 12 hr
Median · 11 hr

Product weight

Lighter than 58% of its class

This model · 212 lb
Median · 216 lb

Published sound level

Quieter than 63% of its class

This model · 74 dBA
Median · 74 dBA

How the score works: Scores use published specs and are relative to comparable products in this catalog. Missing specs are excluded and remaining weights are normalized. Runtime is the longest manufacturer-published figure and may use a different load or fuel than another model.

Size a generator for your own appliances

Starter Fit Score

84/ 100

Strong fit

For a 3,000W target and a $1,500 budget.

Clears your critical profile limits

A score you can inspect and change.

This personal score is separate from the model’s class score. It measures fit against your priorities and gives neutral partial credit when price or noise data is missing.

Power fit

28.5/35

Clears your 3,000W running target.

Budget fit

20/20

$1,399 is within your budget.

Fuel fit

15/15

Dual fuel: gasoline + propane works with your flexible fuel preference.

Portability

4.5/10

212 lb against your medium portability priority.

Noise fit

5.5/10

74 dBA against your medium quietness priority.

Use-case fit

10/10

Home-backup fit rewards adequate output and fuel flexibility.

Tune my profile
Testing, reviews and evidenceCheck hands-on testing status, owner reliability signals, sources, and data confidence.
Checking the hands-on test ledger…

The methods behind every result.

This category-specific protocol defines the questions, equipment, conditions, outputs, and safety gates required for this exact model. Published specifications stay visibly separate from hands-on measurements.

Manufacturer-published baselines

Rated running output

9,500W

Published

Peak / starting output

12,500W

Published

Product weight

212 lb

Published

Published sound level

74 dBA

Published

These numbers organize the test plan. They are not independent confirmations.

Questions the measurements must answer.

01

Planned measurement

Continuous output & regulation

Pending

Can WGen9500DFc hold useful loads without unacceptable voltage or frequency drift?

After manufacturer-specified warm-up, apply a correctly rated resistive load bank at 25%, 50%, 75%, and 100% of rated running output. Hold each step for a defined interval and continuously log watts, volts, frequency, and protective events.

Sustained wattsVoltage rangeFrequency rangeFaults or shutdowns
02

Planned measurement

Starting-load response

Pending

How much voltage and frequency sag occurs during a repeatable stepped starting load?

Use a controlled, instrumented starting-load fixture within published limits. Repeat the same step three times and record the lowest voltage, lowest frequency, recovery time, and whether protection trips.

Peak delivered wattsVoltage sagFrequency sagRecovery time
03

Planned measurement

Fuel use & runtime

Pending

How much usable energy is produced from a measured fuel quantity?

Outdoors at a controlled load, record the starting and ending fuel mass or volume using a safe approved method. Log elapsed time and delivered watt-hours without refueling during the valid measurement window.

Runtime at stated loadFuel per hourkWh per unit of fuelTest fuel and mode
04

Planned measurement

Sound profile

Pending

How loud is the unit under repeatable operating loads?

At an open outdoor site, measure A-weighted sound with a calibrated meter at 7 m / 23 ft on four sides at idle or eco, 25%, 50%, and 75% load. Publish distance, meter response, wind, surface, and ambient level.

dBA by side and loadAmbient dBADistanceOperating mode
05

Planned measurement

Cold & hot starting

Pending

How consistently does the unit start under documented conditions?

Follow the manual exactly and record three ambient-temperature starts plus three heat-soaked restarts. Report attempts, elapsed time, start method, battery state, and any intervention.

Attempts per startStart timeAmbient temperatureStart method

Controlled conditions

  • Record the exact model, serial number, firmware, sample source, and test date before any measurement.
  • Log ambient temperature, humidity, elevation, wind, surface, and background sound for every test block.
  • Record instrument model, range, accuracy, and most recent calibration or verification date.
  • Repeat timing, starting, and sound measurements three times when conditions allow; publish every valid run.
  • Keep original notes, load logs, meter exports, photos, and any excluded-run explanation with the result.

Required equipment class

  • Rated resistive or programmable load bank
  • True-RMS power, voltage, and frequency logger
  • Calibrated Class 1 or Class 2 sound-level meter
  • Approved fuel-measurement equipment and fire protection
  • Weather meter, timer, tachometer, and non-contact thermometer

Safety gate

Operate fuel-burning equipment outdoors only, far from occupied structures, openings, and ignition hazards, with working carbon-monoxide monitoring for personnel.

Testing is for qualified personnel using correctly rated load equipment and the manufacturer’s required grounding, bonding, clearance, and protective-device instructions.

Never connect a generator directly to building wiring or bypass overload, temperature, battery, GFCI, or carbon-monoxide shutdown protection.

Stop a run for unstable voltage or frequency, overheating, fuel or electrolyte leakage, abnormal sound, damaged wiring, or any manufacturer fault indication.

Badge rule: this product receives no “FMG Tested” label or score benefit until a real unit, instruments, conditions, valid runs, raw records, and limitations are documented under the public protocol.

What happens after the honeymoon period?

Long-term reports from confirmed owners show starting, maintenance, failure, support, and recommendation outcomes for the Westinghouse WGen9500DFc.

See how ownership is verified

Verified owners only

Be the first confirmed owner to report back.

Checking reports…

Reliability percentages stay hidden until at least 5 ownership-verified reports are published for this exact model — 5 more needed.

Ownership checked

Purchase or registration evidence is reviewed privately.

Time in service

Reports separate new ownership from 12+ month experience.

Failures documented

Repairs and maintenance are captured, not buried in a star.

Reports stay private while ownership and model details are checked. Contact information is never shown publicly.

Fresh specifications. Visible recall checks.

We show when this record was verified, where its specifications came from, and whether its model number appears in the official CPSC generator-recall dataset.

Review soon

Specification freshness

Last verified
Sep 15, 2026
Review target
Oct 15, 2026

Prices can change faster than technical specifications. Always confirm the current price, exact model number, and manual before purchase.

CPSC model screening

No model-number match found

39 records checked
The Westinghouse WGen9500DFc model text did not match the generator recall records in our current CPSC snapshot. This is a screening result, not a guarantee or safety certification. Recalls can be serial-number specific, newly published, or use a different product description.
Search CPSC directly Dataset checked Sep 16, 2026

Research owner

Founder & lead researcher

Editorial sign-off

Find My Generator Editorial Review

Accountable editor: Andrew Petla

Review scope: exact model identity, published specifications, calculation inputs, source quality, safety language, and affiliate independence. This is an internal editorial review, not third-party engineering, electrical, or safety certification. Hands-on testing is claimed only when a complete test record is published.Request a correction.
Read the full data methodology